SL Green Realty (SLG) 10-K 23 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 22, 2018	Jun. 30, 2017
Document Information [Line Items]
Entity Registrant Name	SL GREEN REALTY CORP
Entity Central Index Key	1,040,971
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		90,327,098
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 9,800,000,000
SL Green Operating Partnership
Document Information [Line Items]
Entity Registrant Name	SL GREEN OPERATING PARTNERSHIP, LP.
Entity Central Index Key	1,492,869
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		1,468,438
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 0

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) shares in Thousands, $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Commercial real estate properties, at cost:
Land and land interests		$ 2,357,051	$ 3,309,710
Building and improvements		6,351,012	7,948,852
Building leasehold and improvements		1,450,614	1,437,325
Properties under capital lease		47,445	47,445
Total commercial real estate properties, at cost		10,206,122	12,743,332
Less: accumulated depreciation		(2,300,116)	(2,264,694)
Total commercial real estate properties, net		7,906,006	10,478,638
Assets held for sale		338,354	0
Cash and cash equivalents		127,888	279,443
Restricted cash		122,138	90,524
Investments in marketable securities		28,579	85,110
Tenant and other receivables, net of allowance of $18,637 and $16,592 in 2017 and 2016, respectively		57,644	53,772
Related party receivables		23,039	15,856
Deferred rents receivable, net of allowance of $17,207 and $25,203 in 2017 and 2016, respectively		365,337	442,179
Debt and preferred equity investments, net of discounts and deferred origination fees of $25,507 and $16,705 in 2017 and 2016, respectively		2,114,041	1,640,412
Investments in unconsolidated joint ventures		2,362,989	1,890,186
Deferred costs, net		226,201	267,600
Other assets		310,688	614,067
Total assets	[1]	13,982,904	15,857,787
Liabilities
Mortgages and other loans payable, net		2,837,282	4,073,830
Revolving credit facility, net		30,336	0
Unsecured term loans, net		1,491,575	1,179,521
Unsecured notes, net		1,395,939	1,128,315
Accrued interest payable		38,142	36,052
Other liabilities		188,005	206,238
Accounts payable and accrued expenses		137,142	190,583
Deferred revenue		208,119	217,955
Capital lease obligations		42,843	42,132
Deferred land leases payable		3,239	2,583
Dividend and distributions payable		85,138	87,271
Security deposits		67,927	66,504
Liabilities related to assets held for sale		4,074	0
Junior subordinated deferrable interest debentures held by trusts that issued trust preferred securities		100,000	100,000
Total liabilities	[1]	6,629,761	7,330,984
Commitments and contingencies		0	0
Noncontrolling interests in Operating Partnership		461,954	473,882
Preferred units		301,735	302,010
Equity
Series I Preferred Stock, $0.01 par value, $25.00 liquidation preference, 9,200 issued and outstanding at both December 31, 2017 and 2016		221,932	221,932
Common stock, $0.01 par value, 160,000 shares authorized and 93,858 and 101,617 issued and outstanding at December 31, 2017 and 2016, respectively (including 1,055 and 1,055 shares held in treasury at December 31, 2017 and 2016, respectively)		939	1,017
Additional paid-in-capital		4,968,338	5,624,545
Treasury stock at cost		(124,049)	(124,049)
Accumulated other comprehensive income		18,604	22,137
Retained earnings		1,139,329	1,578,893
Total SL Green stockholders' equity		6,225,093	7,324,475
Noncontrolling interests in other partnerships		364,361	426,436
Total equity		6,589,454	7,750,911
SL Green stockholders equity:
Total liabilities and equity/capital		$ 13,982,904	$ 15,857,787
Preferred stock, par		$ 0.01	$ 0.01
Preferred stock, liquidation preference		$ 25	$ 25
Preferred stock, shares issued		9,200	9,200
Preferred stock, shares outstanding		9,200	9,200
SL Green Operating Partnership
Commercial real estate properties, at cost:
Land and land interests		$ 2,357,051	$ 3,309,710
Building and improvements		6,351,012	7,948,852
Building leasehold and improvements		1,450,614	1,437,325
Properties under capital lease		47,445	47,445
Total commercial real estate properties, at cost		10,206,122	12,743,332
Less: accumulated depreciation		(2,300,116)	(2,264,694)
Total commercial real estate properties, net		7,906,006	10,478,638
Assets held for sale		338,354	0
Cash and cash equivalents		127,888	279,443
Restricted cash		122,138	90,524
Investments in marketable securities		28,579	85,110
Tenant and other receivables, net of allowance of $18,637 and $16,592 in 2017 and 2016, respectively		57,644	53,772
Related party receivables		23,039	15,856
Deferred rents receivable, net of allowance of $17,207 and $25,203 in 2017 and 2016, respectively		365,337	442,179
Debt and preferred equity investments, net of discounts and deferred origination fees of $25,507 and $16,705 in 2017 and 2016, respectively		2,114,041	1,640,412
Investments in unconsolidated joint ventures		2,362,989	1,890,186
Deferred costs, net		226,201	267,600
Other assets		310,688	614,067
Total assets	[2]	13,982,904	15,857,787
Liabilities
Mortgages and other loans payable, net		2,837,282	4,073,830
Revolving credit facility, net		30,336	0
Unsecured term loans, net		1,491,575	1,179,521
Unsecured notes, net		1,395,939	1,128,315
Accrued interest payable		38,142	36,052
Other liabilities		188,005	206,238
Accounts payable and accrued expenses		137,142	190,583
Deferred revenue		208,119	217,955
Capital lease obligations		42,843	42,132
Deferred land leases payable		3,239	2,583
Dividend and distributions payable		85,138	87,271
Security deposits		67,927	66,504
Liabilities related to assets held for sale		4,074	0
Junior subordinated deferrable interest debentures held by trusts that issued trust preferred securities		100,000	100,000
Total liabilities	[2]	6,629,761	7,330,984
Limited partner interests in SLGOP (4,453 and 4,364 limited partner common units outstanding at December 31, 2017 and 2016, respectively)		461,954	473,882
Preferred units		301,735	302,010
Equity
Accumulated other comprehensive income		18,604	22,137
SL Green stockholders equity:
Series I Preferred Units, $25.00 liquidation preference, 9,200 issued and outstanding at both December 31, 2017 and 2016		221,932	221,932
SL Green partners' capital (973 and 1,049 general partner common units, and 91,831 and 99,513 limited partner common units outstanding at December 31, 2017 and 2016, respectively)		5,984,557	7,080,406
Total SLGOP partners' capital		6,225,093	7,324,475
Noncontrolling interests in other partnerships		364,361	426,436
Total capital		6,589,454	7,750,911
Total liabilities and equity/capital		13,982,904	15,857,787
Consolidated VIEs
Commercial real estate properties, at cost:
Land and land interests		398,000	412,300
Building and improvements		1,400	1,500
Building leasehold and improvements		2,000	2,000
Properties under capital lease		47,400	47,400
Less: accumulated depreciation		(330,900)	(327,200)
Other assets		221,000	226,800
Liabilities
Mortgages and other loans payable, net		628,900	621,800
Accrued interest payable		2,500	2,200
Other liabilities		56,800	72,200
Capital lease obligations		$ 42,800	$ 42,100
[1]	The Company's consolidated balance sheets include assets and liabilities of consolidated variable interest entities ("VIEs"). See Note 2. The consolidated balance sheets include the following amounts related to our consolidated VIEs, excluding the Operating Partnership: $398.0 million and $412.3 million of land, $1.4 billion and $1.5 billion of building and improvements, $2.0 million and $2.0 million of building and leasehold improvements, $47.4 million and $47.4 million of properties under capital lease, $330.9 million and $327.2 million of accumulated depreciation, $221.0 million and $226.8 million of other assets included in other line items, $628.9 million and $621.8 million of real estate debt, net, $2.5 million and $2.2 million of accrued interest payable, $42.8 million and $42.1 million of capital lease obligations, and $56.8 million and $72.2 million of other liabilities included in other line items as of December 31, 2017 and December 31, 2016, respectively.
[2]	The Operating Partnership's consolidated balance sheets include assets and liabilities of consolidated variable interest entities ("VIEs"). See Note 2. The consolidated balance sheets include the following amounts related to our consolidated VIEs: $398.0 million and $412.3 million of land, $1.4 billion and $1.5 billion of building and improvements, $2.0 million and $2.0 million of building and leasehold improvements, $47.4 million and $47.4 million of properties under capital lease, $330.9 million and $327.2 million of accumulated depreciation, $221.0 million and $226.8 million of other assets included in other line items, $628.9 million and $621.8 million of real estate debt, net, $2.5 million and $2.2 million of accrued interest payable, $42.8 million and $42.1 million of capital lease obligations, and $56.8 million and $72.2 million of other liabilities included in other line items as of December 31, 2017 and December 31, 2016, respectively.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Tenant and other receivables, allowance	$ 18,637	$ 16,592
Deferred rents receivable, allowance	17,207	25,203
Discounts and deferred origination fees	$ 25,507	$ 16,705
Preferred stock, par	$ 0.01	$ 0.01
Preferred stock, liquidation preference	$ 25	$ 25
Preferred stock, shares issued	9,200,000	9,200,000
Preferred stock, shares outstanding	9,200,000	9,200,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	160,000,000	160,000,000
Common stock, shares issued	93,858,000	101,617,000
Common stock, shares outstanding	93,858,000	101,617,000
Treasury stock, shares	1,055,000	1,055,000
SL Green Operating Partnership
Tenant and other receivables, allowance	$ 18,637	$ 16,592
Deferred rents receivable, allowance	17,207	25,203
Discounts and deferred origination fees	$ 25,507	$ 16,705
Limited partner interests in Operating Partnership, limited partner common units outstanding (shares)	4,453,000	4,364,000
Preferred units, liquidation preference (in dollars per share)	$ 25	$ 25
Preferred units, shares issued	9,200,000	9,200,000
Preferred units, shares outstanding	9,200,000	9,200,000
SL Green partner's capital, general partner common units outstanding (shares)	973,000	1,049,000
SL Green partners' capital, limited partner common units outstanding (shares)	91,831,000	99,513,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Rental revenue, net	$ 1,100,993	$ 1,323,767	$ 1,245,981
Escalation and reimbursement	172,939	196,858	178,512
Investment income	193,871	213,008	181,128
Other income	43,670	130,348	57,208
Total revenues	1,511,473	1,863,981	1,662,829
Expenses
Operating expenses, including $21,400 in 2017, $21,890 in 2016, $20,071 in 2015 of related party expenses	293,364	312,859	301,624
Real estate taxes	244,323	248,388	232,702
Ground rent	33,231	33,261	32,834
Interest expense, net of interest income	257,045	321,199	323,870
Amortization of deferred financing costs	16,498	24,564	27,348
Depreciation and amortization	403,320	821,041	560,887
Transaction related costs	(1,834)	7,528	11,430
Marketing, general and administrative	100,498	99,759	94,873
Total expenses	1,346,445	1,868,599	1,585,568
Income (loss) from continuing operations before equity in net income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, gain (loss) on sale of marketable securities and loss on early extinguishment of debt	165,028	(4,618)	77,261
Equity in net income from unconsolidated joint ventures	21,892	11,874	13,028
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	16,166	44,009	15,844
Purchase price fair value adjustment	0	0	40,078
Gain on sale of real estate, net	73,241	238,116	175,974
Depreciable real estate reserves	(178,520)	(10,387)	(19,226)
Gain (loss) on sale of investment in marketable securities	3,262	(83)	0
Loss on early extinguishment of debt	0	0	(49)
Income from continuing operations	101,069	278,911	302,910
Net income from discontinued operations	0	0	427
Gain on sale of discontinued operations	0	0	14,122
Net income	101,069	278,911	317,459
Net (income) loss attributable to noncontrolling interests:
Noncontrolling interests in the Operating Partnership	(3,995)	(10,136)	(10,565)
Net (income) loss attributable to noncontrolling interests in other partnerships	15,701	(7,644)	(15,843)
Preferred unit distributions	(11,401)	(11,235)	(6,967)
Net income (loss) attributable to SL Green/SLGOP	101,374	249,896	284,084
Preferred stock/unit redemption costs	0	0	0
Perpetual preferred stock dividends	(14,950)	(14,950)	(14,952)
Amounts attributable to SL Green common stockholders:
Income (loss) from continuing operations before purchase price fair value adjustment, gains on sale and discontinued operations	171,600	(25,552)	50,502
Purchase price fair value adjustment	0	0	38,563
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	15,452	42,189	15,245
Net income from discontinued operations	0	0	411
Gain on sale of discontinued operations	0	0	13,588
Gain on sale of real estate, net	70,005	228,266	169,322
Depreciable real estate reserves	(170,633)	(9,957)	(18,499)
Net income attributable to SL Green common stockholders	$ 86,424	$ 234,946	$ 269,132
Basic earnings per share:
Income from continuing operations before purchase price fair value adjustment, gains on sale and discontinued operations (usd per share)	$ 1.74	$ (0.26)	$ 0.51
Purchase price fair value adjustment (usd per share)	0	0	0.39
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (usd per share)	0.16	0.42	0.15
Net income from discontinued operations (usd per share)	0	0	0
Gain on sale of discontinued operations (usd per share)	0	0	0.14
Gain on sale of real estate (in dollars per share)	0.71	2.29	1.71
Depreciable real estate reserves (in dollars per share)	(1.73)	(0.10)	(0.19)
Net income attributable to SL Green common stockholders (usd per share)	0.88	2.35	2.71
Diluted earnings per share:
Income from continuing operations before purchase price fair value adjustment, gains on sale and discontinued operations (usd per share)	1.74	(0.25)	0.51
Purchase price fair value adjustment (usd per share)	0	0	0.39
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (usd per share)	0.16	0.42	0.15
Net income from discontinued operations (usd per share)	0	0	0
Gain on sale of discontinued operations (usd per share)	0	0	0.14
Gain on sale of real estate (in dollars per share)	0.71	2.27	1.70
Depreciable real estate reserves (in dollars per share)	(1.74)	(0.10)	(0.19)
Net income attributable to SL Green common stockholders (usd per share)	$ 0.87	$ 2.34	$ 2.70
Basic weighted average common shares outstanding (in shares)	98,571	100,185	99,345
Diluted weighted average common shares and common share equivalents outstanding (in shares)	103,403	104,881	103,734
SL Green Operating Partnership
Revenues
Rental revenue, net	$ 1,100,993	$ 1,323,767	$ 1,245,981
Escalation and reimbursement	172,939	196,858	178,512
Investment income	193,871	213,008	181,128
Other income	43,670	130,348	57,208
Total revenues	1,511,473	1,863,981	1,662,829
Expenses
Operating expenses, including $21,400 in 2017, $21,890 in 2016, $20,071 in 2015 of related party expenses	293,364	312,859	301,624
Real estate taxes	244,323	248,388	232,702
Ground rent	33,231	33,261	32,834
Interest expense, net of interest income	257,045	321,199	323,870
Amortization of deferred financing costs	16,498	24,564	27,348
Depreciation and amortization	403,320	821,041	560,887
Transaction related costs	(1,834)	7,528	11,430
Marketing, general and administrative	100,498	99,759	94,873
Total expenses	1,346,445	1,868,599	1,585,568
Income (loss) from continuing operations before equity in net income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, gain (loss) on sale of marketable securities and loss on early extinguishment of debt	165,028	(4,618)	77,261
Equity in net income from unconsolidated joint ventures	21,892	11,874	13,028
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	16,166	44,009	15,844
Purchase price fair value adjustment	0	0	40,078
Gain on sale of real estate, net	73,241	238,116	175,974
Depreciable real estate reserves	(178,520)	(10,387)	(19,226)
Gain (loss) on sale of investment in marketable securities	3,262	(83)	0
Loss on early extinguishment of debt	0	0	(49)
Income from continuing operations	101,069	278,911	302,910
Net income from discontinued operations	0	0	427
Gain on sale of discontinued operations	0	0	14,122
Net income	101,069	278,911	317,459
Net (income) loss attributable to noncontrolling interests:
Net (income) loss attributable to noncontrolling interests in other partnerships	15,701	(7,644)	(15,843)
Preferred unit distributions	(11,401)	(11,235)	(6,967)
Net income (loss) attributable to SL Green/SLGOP	105,369	260,032	294,649
Preferred stock/unit redemption costs	0	0	0
Perpetual preferred stock dividends	(14,950)	(14,950)	(14,952)
Net income attributable to SLGOP common unitholders	90,419	245,082	279,697
Amounts attributable to SL Green common stockholders:
Income (loss) from continuing operations before purchase price fair value adjustment, gains on sale and discontinued operations	179,532	(26,656)	52,478
Purchase price fair value adjustment	0	0	40,078
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	16,166	44,009	15,844
Net income from discontinued operations	0	0	427
Gain on sale of discontinued operations	0	0	14,122
Gain on sale of real estate, net	73,241	238,116	175,974
Depreciable real estate reserves	$ (178,520)	$ (10,387)	$ (19,226)
Basic earnings per share:
Income from continuing operations before gains on sale and discontinued operations (usd per share)	$ 1.74	$ (0.26)	$ 0.51
Purchase price fair value adjustment (usd per share)	0	0	0.39
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (usd per share)	0.16	0.42	0.15
Net income from discontinued operations (usd per share)	0	0	0
Gain on sale of discontinued operations (usd per share)	0	0	0.14
Gain on sale of real estate (in dollars per share)	0.71	2.29	1.71
Depreciable real estate reserves (in dollars per share)	(1.73)	(0.10)	(0.19)
Net income attributable to SLGOP common unitholders (usd per share)	0.88	2.35	2.71
Diluted earnings per share:
Income from continuing operations before gains on sale and discontinued operations (usd per share)	1.74	(0.25)	0.51
Purchase price fair value adjustment (usd per share)	0	0	0.39
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (usd per share)	0.16	0.42	0.15
Net income from discontinued operations (usd per share)	0	0	0
Gain on sale of discontinued operations (usd per share)	0	0	0.14
Gain on sale of real estate (in dollars per share)	0.71	2.27	1.70
Depreciable real estate reserves (in dollars per share)	(1.74)	(0.10)	(0.19)
Net income attributable to SLGOP common unitholders (usd per share)	$ 0.87	$ 2.34	$ 2.70
Basic weighted average common shares outstanding (in shares)	103,127	104,508	103,244
Basic weighted average common units outstanding (in shares)	103,127	104,508	103,244
Diluted weighted average common shares and common share equivalents outstanding (in shares)	103,403	104,881	103,734
Diluted weighted average common units and common unit equivalents outstanding (in shares)	103,403	104,881	103,734

Consolidated Statements of Ope5

Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses, paid to related parties	$ 21,400	$ 21,890	$ 20,071
SL Green Operating Partnership
Operating expenses, paid to related parties	$ 21,400	$ 21,890	$ 20,071

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income	$ 101,069	$ 278,911	$ 317,459
Other comprehensive income:
Change in net unrealized (loss) gain on derivative instruments, including SL Green's/SLGOP's share of joint venture net unrealized (loss) gain on derivative instruments	1,040	28,508	(1,229)
Change in unrealized gain on marketable securities	(4,667)	3,677	(607)
Other comprehensive (loss) income	(3,627)	32,185	(1,836)
Comprehensive income	97,442	311,096	315,623
Net loss (income) attributable to noncontrolling interests and preferred units distributions	305	(29,015)	(33,375)
Net loss (income) attributable to noncontrolling interests	15,701	(7,644)	(15,843)
Other comprehensive income (loss) attributable to noncontrolling interests	94	(1,299)	67
Comprehensive income attributable to SL Green/SLGOP	97,841	280,782	282,315
SL Green Operating Partnership
Net income	101,069	278,911	317,459
Other comprehensive income:
Change in net unrealized (loss) gain on derivative instruments, including SL Green's/SLGOP's share of joint venture net unrealized (loss) gain on derivative instruments	1,040	28,508	(1,229)
Change in unrealized gain on marketable securities	(4,667)	3,677	(607)
Other comprehensive (loss) income	(3,627)	32,185	(1,836)
Comprehensive income	97,442	311,096	315,623
Net loss (income) attributable to noncontrolling interests	15,701	(7,644)	(15,843)
Other comprehensive income (loss) attributable to noncontrolling interests	94	(1,299)	67
Comprehensive income attributable to SL Green/SLGOP	$ 113,237	$ 302,153	$ 299,847

Consolidated Statement of Equit

Consolidated Statement of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid- In-Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Noncontrolling Interests	Series I Preferred StockPreferred Stock
Beginning Balance at Dec. 31, 2014	$ 7,459,216	$ 974	$ 5,113,759	$ 0	$ (6,980)	$ 1,607,689	$ 521,842	$ 221,932
Beginning Balance (in shares) at Dec. 31, 2014		97,325
Increase (Decrease) in Stockholders' Equity
Net income (loss)	299,927					284,084	15,843
Acquisition of subsidiary interest from noncontrolling interest	(20,650)		(9,566)				(11,084)
Other comprehensive income	(1,769)				(1,769)
Preferred dividends	(14,952)					(14,952)
DRSPP (in shares)		776
DRSPP proceeds	99,555	$ 8	99,547
Conversion of units of the Operating Partnership to common stock (in shares)		483
Redemption of units in the operating partnership	55,697	$ 5	55,692
Reallocation of noncontrolling interest in the Operating Partnership	20,915					20,915
Deferred compensation plan and stock award, net (in shares)		168
Deferred compensation plan and stock award, net	(2,982)	$ 2	243			(3,227)
Reallocation of capital account relating to sale	(10,143)						(10,143)
Amortization of deferred compensation plan	26,721		26,721
Issuance of common stock (in shares)		1,007
Issuance of common stock	126,989	$ 10	136,979	(10,000)
Proceeds from stock options exercised (in shares)		217
Proceeds from stock options exercised	16,362	$ 2	16,360
Contributions to consolidated joint venture interests	35,178						35,178
Cash distributions to noncontrolling interests	(119,784)						(119,784)
Cash distributions declared ($2.52, $2.10, and $1.49 per common share, respectively, none of which represented a return of capital for federal income tax purposes)	(250,963)					(250,963)
Ending Balance at Dec. 31, 2015	7,719,317	$ 1,001	5,439,735	(10,000)	(8,749)	1,643,546	431,852	221,932
Ending Balance (in shares) at Dec. 31, 2015		99,976
Increase (Decrease) in Stockholders' Equity
Net income (loss)	257,540					249,896	7,644
Other comprehensive income	30,886				30,886
Preferred dividends	(14,950)					(14,950)
DRSPP (in shares)		2
DRSPP proceeds	277		277
Conversion of units of the Operating Partnership to common stock (in shares)		295
Redemption of units in the operating partnership	31,806	$ 3	31,803
Reallocation of noncontrolling interest in the Operating Partnership	(4,222)					(4,222)
Deferred compensation plan and stock award, net (in shares)		96
Deferred compensation plan and stock award, net	(1,988)	$ 1	(1,989)
Amortization of deferred compensation plan	25,890		25,890
Issuance of common stock (in shares)
Issuance of common stock	(40)	$ 10	113,999	(114,049)
Proceeds from stock options exercised (in shares)		193
Proceeds from stock options exercised	14,832	$ 2	14,830
Contributions to consolidated joint venture interests	2,359						2,359
Cash distributions to noncontrolling interests	(15,419)						(15,419)
Cash distributions declared ($2.52, $2.10, and $1.49 per common share, respectively, none of which represented a return of capital for federal income tax purposes)	(295,377)					(295,377)
Ending Balance at Dec. 31, 2016	7,750,911	$ 1,017	5,624,545	(124,049)	22,137	1,578,893	426,436	221,932
Ending Balance (in shares) at Dec. 31, 2016		100,562
Increase (Decrease) in Stockholders' Equity
Net income (loss)	85,673					101,374	(15,701)
Other comprehensive income	(3,533)				(3,533)
Preferred dividends	(14,950)					(14,950)
DRSPP (in shares)		2
DRSPP proceeds	223		223
Conversion of units of the Operating Partnership to common stock (in shares)		202
Redemption of units in the operating partnership	21,574	$ 2	21,572
Reallocation of noncontrolling interest in the Operating Partnership	5,712					5,712
Equity component of repurchased exchangeable senior notes	(109,776)		(109,776)
Deferred compensation plan and stock award, net (in shares)		87
Deferred compensation plan and stock award, net	(2,374)	$ 1	(2,375)
Amortization of deferred compensation plan	32,161		32,161
Repurchases of common stock (in shares)		(8,342)
Repurchases of common stock	(848,048)	$ (83)	(621,324)			(226,641)
Proceeds from stock options exercised (in shares)		292
Proceeds from stock options exercised	23,314	$ 2	23,312
Contributions to consolidated joint venture interests	36,275						36,275
Deconsolidation of partially owned entity	(30,203)						(30,203)
Cash distributions to noncontrolling interests	(52,446)						(52,446)
Cash distributions declared ($2.52, $2.10, and $1.49 per common share, respectively, none of which represented a return of capital for federal income tax purposes)	(305,059)					(305,059)
Ending Balance at Dec. 31, 2017	$ 6,589,454	$ 939	$ 4,968,338	$ (124,049)	$ 18,604	$ 1,139,329	$ 364,361	$ 221,932
Ending Balance (in shares) at Dec. 31, 2017		92,803

Consolidated Statement of Equi8

Consolidated Statement of Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Cash distribution declared, per common share (in dollars per share)	$ 3.14	$ 2.94	$ 2.52

Consolidated Statement of Capit

Consolidated Statement of Capital - USD ($) shares in Thousands, $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Partner's Capital
Acquisition of subsidiary interest from noncontrolling interest							$ (20,650)
Preferred distributions	$ (6,616)	$ 14,165	$ (6,217)	$ (5,544)
Conversion of common units					$ 21,574	$ 31,806	55,697
DRSPP proceeds					223	277	99,555
Reallocation of capital account relating to sale							(10,143)
Reallocation of noncontrolling interests in the operating partnership					5,712	(4,222)	20,915
Equity component of repurchased exchangeable senior notes					(109,776)
Amortization of deferred compensation plan					32,161	25,890	26,721
Proceeds from stock options exercised					23,314	14,832	16,362
Deconsolidation of partially owned entity					(30,203)
Cash distributions to noncontrolling interests					(52,446)	(15,419)	(119,784)
Common Stock
Increase (Decrease) in Partner's Capital
Conversion of common units					$ 2	$ 3	$ 5
DRSPP (in units)					2	2	776
DRSPP proceeds							$ 8
Proceeds from stock options exercised (in shares)					292	193	217
Proceeds from stock options exercised					$ 2	$ 2	$ 2
Contributions - net proceeds from common stock offering (in units)							1,007
Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Acquisition of subsidiary interest from noncontrolling interest							$ (11,084)
Reallocation of capital account relating to sale							(10,143)
Deconsolidation of partially owned entity					(30,203)
Cash distributions to noncontrolling interests					(52,446)	$ (15,419)	(119,784)
SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Beginning Balance		7,750,911		7,719,317	7,750,911	7,719,317	7,459,216
Net income					85,673	257,540	299,927
Acquisition of subsidiary interest from noncontrolling interest							(20,650)
Other comprehensive (loss)					(3,533)	30,886	(1,769)
Preferred distributions	(5,328)	14,641	(4,252)	(4,622)	(14,950)	(14,950)	(14,952)
Conversion of common units					21,574	31,806	55,697
DRSPP proceeds					223	277	99,555
Reallocation of capital account relating to sale							(10,143)
Reallocation of noncontrolling interests in the operating partnership					5,712	(4,222)	20,915
Equity component of repurchased exchangeable senior notes					(109,776)
Deferred compensation plan and stock award, net					(2,374)	(1,988)	(2,982)
Amortization of deferred compensation plan					32,161	25,890	26,721
Repurchases of common stock					(848,048)
Proceeds from stock options exercised					23,314
Issuance of stock						(40)
Contribution to consolidated joint venture interests					36,275	2,359	35,178
Deconsolidation of partially owned entity					(30,203)
Contributions - net proceeds from common stock offering							126,989
Contributions - proceeds from stock options exercised						14,832	16,362
Cash distributions to noncontrolling interests					(52,446)	(15,419)	(119,784)
Cash distributions declared ($3.1375, $2.94, and $2.52 per common unit, respectively, none of which represented a return of capital for federal income tax purposes)					(305,059)	(295,377)	(250,963)
Ending Balance	6,589,454		7,750,911		6,589,454	7,750,911	7,719,317
SL Green Operating Partnership | Preferred Units | Series I Preferred Stock
Increase (Decrease) in Partner's Capital
Beginning Balance		221,932		221,932	221,932	221,932	221,932
Ending Balance	221,932		221,932		221,932	221,932	221,932
SL Green Operating Partnership | Common Stock | Partners' Interest
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 7,080,406		$ 7,074,282	$ 7,080,406	$ 7,074,282	$ 6,722,422
Beginning Balance (units)		100,562		99,976	100,562	99,976	97,325
Net income					$ 101,374	$ 249,896	$ 284,084
Acquisition of subsidiary interest from noncontrolling interest							(9,566)
Preferred distributions					$ (14,950)	$ (14,950)	$ (14,952)
Conversion of common units (in units)					202	295	483
Conversion of common units					$ 21,574	$ 31,806	$ 55,697
DRSPP (in units)					2		776
DRSPP proceeds					$ 223	277	$ 99,555
Reallocation of noncontrolling interests in the operating partnership					5,712	$ (4,222)	$ 20,915
Equity component of repurchased exchangeable senior notes					$ (109,776)
Deferred compensation plan and stock award, net, (in units)					87	96	168
Deferred compensation plan and stock award, net					$ (2,374)	$ (1,988)	$ (2,982)
Amortization of deferred compensation plan					$ 32,161	25,890	$ 26,721
Repurchases of common stock (in units)					(8,342)
Proceeds from stock options exercised (in shares)					292
Proceeds from stock options exercised					$ 23,314
Issuance of stock						$ 40
Contributions - net proceeds from common stock offering (in units)							1,007
Contributions - net proceeds from common stock offering							$ 126,989
Contributions - proceeds from stock options exercised (in units)						193	217
Contributions - proceeds from stock options exercised						$ 14,832	$ 16,362
Cash distributions declared ($3.1375, $2.94, and $2.52 per common unit, respectively, none of which represented a return of capital for federal income tax purposes)					(305,059)	295,377	(250,963)
Ending Balance	$ 5,984,557		$ 7,080,406		$ 5,984,557	$ 7,080,406	$ 7,074,282
Ending Balance (units)	92,803		100,562		92,803	100,562	99,976
SL Green Operating Partnership | Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 22,137		$ (8,749)	$ 22,137	$ (8,749)	$ (6,980)
Other comprehensive (loss)					(3,533)	30,886	(1,769)
Ending Balance	$ 18,604		$ 22,137		18,604	22,137	(8,749)
SL Green Operating Partnership | Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 426,436		$ 431,852	426,436	431,852	521,842
Net income					(15,701)	7,644	15,843
Acquisition of subsidiary interest from noncontrolling interest							(11,084)
Reallocation of capital account relating to sale							(10,143)
Contribution to consolidated joint venture interests					36,275	2,359	35,178
Deconsolidation of partially owned entity					(30,203)
Cash distributions to noncontrolling interests					(52,446)	15,419	(119,784)
Ending Balance	$ 364,361		$ 426,436		$ 364,361	$ 426,436	$ 431,852

Consolidated Statement of Cap10

Consolidated Statement of Capital (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash distribution declared, per common share (in dollars per share)	$ 3.14	$ 2.94	$ 2.52
SL Green Operating Partnership
Cash distribution declared, per common share (in dollars per share)	$ 3.1375	$ 2.94	$ 2.52

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Operating Activities
Net income		$ 101,069		$ 278,911	$ 317,459
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		419,818		845,605	588,238
Equity in net income from unconsolidated joint ventures		(21,892)		(11,874)	(13,028)
Distributions of cumulative earnings from unconsolidated joint ventures		20,309		24,337	40,759
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate		(16,166)		(44,009)	(15,844)
Purchase price fair value adjustment		0		0	(40,078)
Depreciable real estate reserves		178,520		10,387	19,226
Gain on sale of real estate, net		(73,241)		(238,116)	(175,974)
Gain on sale of discontinued operations		0		0	(14,122)
(Gain) loss on sale of investments in marketable securities		(3,262)		83	0
Loss on early extinguishment of debt		0		0	49
Deferred rents receivable		(38,009)		26,716	(136,924)
Other non-cash adjustments	[1]	17,196		(150,913)	(20,671)
Changes in operating assets and liabilities:
Restricted cash—operations		7,147		(10,811)	11,289
Tenant and other receivables		(5,717)		4,780	(6,405)
Related party receivables		(7,209)		(5,183)	1,278
Deferred lease costs		(41,939)		(70,707)	(61,005)
Other assets		(23,068)		9,899	18,501
Accounts payable, accrued expenses and other liabilities and security deposits		(11,790)		(35,628)	8,634
Deferred revenue and land leases payable		46,607		1,237	5,102
Net cash provided by operating activities		548,373		634,714	526,484
Investing Activities
Acquisitions of real estate property		(13,680)		(37,760)	(2,653,311)
Additions to land, buildings and improvements		(335,253)		(411,950)	(406,442)
Escrowed cash—capital improvements/acquisition deposits/deferred purchase price		(3,499)		92,374	(101,000)
Investments in unconsolidated joint ventures		(389,249)		(84,456)	(161,712)
Distributions in excess of cumulative earnings from unconsolidated joint ventures		319,745		196,211	98,639
Proceeds from disposition of real estate/joint venture interest		639,682		2,469,719	1,216,785
Proceeds from sale of marketable securities		55,129		6,965	1,426
Purchases of marketable securities		0		(43,341)	(7,769)
Other investments		25,330		7,704	(15,806)
Origination of debt and preferred equity investments		(1,129,970)		(977,413)	(756,939)
Repayments or redemption of debt and preferred equity investments		812,914		904,517	520,218
Net cash (used in) provided by investing activities		(18,851)		2,122,570	(2,265,911)
Financing Activities
Proceeds from mortgages and other loans payable		870,459		408,293	1,849,293
Repayments of mortgages and other loans payable		(902,460)		(1,822,303)	(781,236)
Proceeds from revolving credit facility, term loans and senior unsecured notes		2,784,599		1,325,300	2,515,000
Repayments of revolving credit facility, term loans and senior unsecured notes		(2,276,782)		(2,334,604)	(1,706,007)
Payments of debt extinguishment costs		0		0	0
Proceeds from stock options exercised and DRSPP issuance		23,537		15,109	115,917
Proceeds from sale of common stock		0		0	124,761
Repurchase of common stock		(806,302)		0	0
Redemption of preferred stock		(275)		(3,299)	(200)
Distributions to noncontrolling interests in other partnerships		(52,446)		(15,419)	(119,784)
Contributions from noncontrolling interests in other partnerships		36,275		2,359	12,674
Distributions to noncontrolling interests in the Operating Partnership		(14,266)		(12,671)	(9,710)
Dividends/Distributions paid on common and preferred stock/units		(333,543)		(314,079)	(257,378)
Other obligations related to mortgage loan participations		17,227		59,150	25,000
Deferred loan costs and capitalized lease obligation		(27,100)		(41,076)	(54,913)
Net cash (used in) provided by financing activities		(681,077)		(2,733,240)	1,713,417
Net (decrease) increase in cash and cash equivalents		(151,555)		24,044	(26,010)
Cash and cash equivalents at beginning of year		279,443		255,399	281,409
Cash and cash equivalents at end of period		127,888		279,443	255,399
Supplemental Cash Flow Information [Abstract]
Interest paid		273,819		344,295	345,110
Income taxes paid		2,448		2,009	3,882
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the operating partnership		25,723		78,495	30,506
Redemption of units in the operating partnership		21,574		31,806	55,697
Derivative instruments at fair value		4,397		31,826	1,816
Exchange of debt investment for equity in joint venture		0		68,581	10,151
Acquisition of subsidiary interest from noncontrolling interest		0		0	20,630
Tenant improvements and capital expenditures payable		6,667		15,972	7,755
Fair value adjustment to noncontrolling interest in operating partnership		5,712		4,222	20,915
Assumption of mortgage loan		0		0	112,795
Capital lease assets		0		0	20,000
Reclassification of development costs from other assets to real estate		0		0	47,519
Deconsolidation of a subsidiary	[2]	695,204		1,226,425	27,435
Transfer of assets to assets held for sale		611,809		2,048,376	34,981
Transfer of liabilities related to assets held for sale		5,364		1,677,528	29,000
Consolidation of real estate investment		0		0	158,566
Removal of fully depreciated commercial real estate properties		15,488		31,474	241,910
Issuance of SLG's common stock to a consolidated joint venture		0		114,049	10,000
Contribution to consolidated joint venture by noncontrolling interest		0		0	22,504
Share repurchase payable		41,746		0	0
SL Green Operating Partnership
Operating Activities
Net income		101,069		278,911	317,459
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		419,818		845,605	588,238
Equity in net income from unconsolidated joint ventures		(21,892)		(11,874)	(13,028)
Distributions of cumulative earnings from unconsolidated joint ventures		20,309		24,337	40,759
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate		(16,166)		(44,009)	(15,844)
Purchase price fair value adjustment		0		0	(40,078)
Depreciable real estate reserves		178,520		10,387	19,226
Gain on sale of real estate, net		(73,241)		(238,116)	(175,974)
Gain on sale of discontinued operations		0		0	(14,122)
(Gain) loss on sale of investments in marketable securities		(3,262)		83	0
Loss on early extinguishment of debt		0		0	49
Deferred rents receivable		(38,009)		26,716	(136,924)
Other non-cash adjustments		17,196	[1]	(150,913)	(20,671)
Changes in operating assets and liabilities:
Restricted cash—operations		7,147		(10,811)	11,289
Tenant and other receivables		(5,717)		4,780	(6,405)
Related party receivables		(7,209)		(5,183)	1,278
Deferred lease costs		(41,939)		(70,707)	(61,005)
Other assets		(23,068)		9,899	18,501
Accounts payable, accrued expenses and other liabilities and security deposits		(11,790)		(35,628)	8,634
Deferred revenue and land leases payable		46,607		1,237	5,102
Net cash provided by operating activities		548,373		634,714	526,484
Investing Activities
Acquisitions of real estate property		(13,680)		(37,760)	(2,653,311)
Additions to land, buildings and improvements		(335,253)		(411,950)	(406,442)
Escrowed cash—capital improvements/acquisition deposits/deferred purchase price		(3,499)		92,374	(101,000)
Investments in unconsolidated joint ventures		(389,249)		(84,456)	(161,712)
Distributions in excess of cumulative earnings from unconsolidated joint ventures		319,745		196,211	98,639
Proceeds from disposition of real estate/joint venture interest		639,682		2,469,719	1,216,785
Proceeds from sale of marketable securities		55,129		6,965	1,426
Purchases of marketable securities		0		(43,341)	(7,769)
Other investments		25,330		7,704	(15,806)
Origination of debt and preferred equity investments		(1,129,970)		(977,413)	(756,939)
Repayments or redemption of debt and preferred equity investments		812,914		904,517	520,218
Net cash (used in) provided by investing activities		(18,851)		2,122,570	(2,265,911)
Financing Activities
Proceeds from mortgages and other loans payable		870,459		408,293	1,849,293
Repayments of mortgages and other loans payable		(902,460)		(1,822,303)	(781,236)
Proceeds from revolving credit facility, term loans and senior unsecured notes		2,784,599		1,325,300	2,515,000
Repayments of revolving credit facility, term loans and senior unsecured notes		(2,276,782)		(2,334,604)	(1,706,007)
Payments of debt extinguishment costs		0		0	0
Proceeds from stock options exercised and DRSPP issuance		23,537		15,109	115,917
Proceeds from sale of common stock		0		0	124,761
Repurchase of common stock		(806,302)		0	0
Redemption of preferred stock		(275)		(3,299)	(200)
Distributions to noncontrolling interests in other partnerships		(52,446)		(15,419)	(119,784)
Contributions from noncontrolling interests in other partnerships		36,275		2,359	12,674
Dividends/Distributions paid on common and preferred stock/units		(347,809)		(326,750)	(267,088)
Other obligations related to mortgage loan participations		17,227		59,150	25,000
Deferred loan costs and capitalized lease obligation		(27,100)		(41,076)	(54,913)
Net cash (used in) provided by financing activities		(681,077)		(2,733,240)	1,713,417
Net (decrease) increase in cash and cash equivalents		(151,555)		24,044	(26,010)
Cash and cash equivalents at beginning of year		279,443		255,399	281,409
Cash and cash equivalents at end of period		127,888		279,443	255,399
Supplemental Cash Flow Information [Abstract]
Interest paid		273,819		344,295	345,110
Income taxes paid		2,448		2,009	3,882
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the operating partnership		25,723		78,495	30,506
Derivative instruments at fair value		4,397		31,826	1,816
Exchange of debt investment for equity in joint venture		0		68,581	10,151
Acquisition of subsidiary interest from noncontrolling interest		0		0	20,630
Tenant improvements and capital expenditures payable		6,667		15,972	7,755
Fair value adjustment to noncontrolling interest in operating partnership		5,712		4,222	20,915
Assumption of mortgage loan		0		0	112,795
Capital lease assets		0		0	20,000
Reclassification of development costs from other assets to real estate		0		0	47,519
Deconsolidation of a subsidiary	[2]	695,204		1,226,425	27,435
Transfer of assets to assets held for sale		611,809		2,048,376	34,981
Transfer of liabilities related to assets held for sale		5,364		1,677,528	29,000
Consolidation of real estate investment		0		0	158,566
Removal of fully depreciated commercial real estate properties		15,488		31,474	241,910
Issuance of SLG's common stock to a consolidated joint venture		0		114,049	10,000
Contribution to consolidated joint venture by noncontrolling interest		0		0	22,504
Share repurchase payable		41,746		0	0
Common Stock
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition		0		0	2,228
Common Stock | SL Green Operating Partnership
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition		0		0	2,228
Preferred Units
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition		0		22,793	211,601
Preferred Units | SL Green Operating Partnership
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition		$ 0		$ 22,793	$ 211,601
[1]	Included in Other non-cash adjustments is $172.4 million for the year ended December 31, 2016 for the amortization of the below-market lease at 388-390 Greenwich Street as a result of the tenant exercising their option to purchase the property and entering into an agreement to accelerate the sale.
[2]	$366.6 million of the 2017 amount relates to 1515 Broadway. In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. See Note 6, "Investments in Unconsolidated Joint Ventures.".

Consolidated Statements of Ca12

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
		Nov. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly distributions declared, per share/unit (usd per share/unit)			$ 0.8125	$ 0.775	$ 0.72
Deconsolidation of a subsidiary	[1]		$ 695,204	$ 1,226,425	$ 27,435
SL Green Operating Partnership
Quarterly distributions declared, per share/unit (usd per share/unit)			$ 0.8125	$ 0.775	$ 0.72
Deconsolidation of a subsidiary	[1]		$ 695,204	$ 1,226,425	$ 27,435
388-390 Greenwich Street
Amortization of below market leases				172,400
388-390 Greenwich Street | SL Green Operating Partnership
Amortization of below market leases				$ 172,400
Allianz Real Estate | 1515 Broadway
Deconsolidation of a subsidiary		$ 366,600
Ownership percentage in disposed asset		30.13%
[1]	$366.6 million of the 2017 amount relates to 1515 Broadway. In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. See Note 6, "Investments in Unconsolidated Joint Ventures.".

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	Organization and Basis of Presentation SL Green Realty Corp., which is referred to as the Company or SL Green, a Maryland corporation, and SL Green Operating Partnership, L.P., which is referred to as SLGOP or the Operating Partnership, a Delaware limited partnership, were formed in June 1997 for the purpose of combining the commercial real estate business of S.L. Green Properties, Inc. and its affiliated partnerships and entities. The Operating Partnership received a contribution of interest in the real estate properties, as well as 95% of the economic interest in the management, leasing and construction companies which are referred to as the Service Corporation. All of the management, leasing and construction services that are provided to the properties that are wholly-owned by us and that are provided to certain joint ventures are conducted through SL Green Management LLC which is 100% owned by the Operating Partnership. The Company has qualified, and expects to qualify in the current fiscal year, as a real estate investment trust, or REIT, under the Internal Revenue Code of 1986, as amended, or the Code, and operates as a self-administered, self-managed REIT. A REIT is a legal entity that holds real estate interests and, through payments of dividends to stockholders, is permitted to minimize the payment of Federal income taxes at the corporate level. Unless the context requires otherwise, all references to "we," "our" and "us" means the Company and all entities owned or controlled by the Company, including the Operating Partnership. Substantially all of our assets are held by, and all of our operations are conducted through, the Operating Partnership. The Company is the sole managing general partner of the Operating Partnership. As of December 31, 2017 , noncontrolling investors held, in the aggregate, a 4.58% limited partnership interest in the Operating Partnership. We refer to these interests as the noncontrolling interests in the Operating Partnership. The Operating Partnership is considered a variable interest entity, or VIE, in which we are the primary beneficiary. See Note 11, "Noncontrolling Interests on the Company's Consolidated Financial Statements." Reckson Associates Realty Corp., or Reckson, and Reckson Operating Partnership, L.P., or ROP, are wholly-owned subsidiaries of SL Green Realty Corp. As of December 31, 2017 , we owned the following interests in properties in the New York metropolitan area, primarily in midtown Manhattan. Our investments located outside of Manhattan are referred to as the Suburban properties: Consolidated Unconsolidated Total Location Property Type Number of Properties Approximate Square Feet (unaudited) Number of Properties Approximate Square Feet (unaudited) Number of Properties Approximate Square Feet (unaudited) Weighted Average Occupancy (1) (unaudited) Commercial: Manhattan Office 23 (2) 14,304,606 9 10,356,864 32 24,661,470 93.9 % Retail 4 (3) 302,583 9 347,970 13 650,553 94.5 % Development/Redevelopment 7 158,985 4 770,514 11 929,499 63.8 % Fee Interest 1 176,530 1 — 2 176,530 100.0 % 35 14,942,704 23 11,475,348 58 26,418,052 92.9 % Suburban Office 20 (4 ) 3,013,200 2 640,000 22 3,653,200 84.0 % Retail 1 52,000 — — 1 52,000 100.0 % Development/Redevelopment 1 1,000 1 — 2 1,000 100.0 % 22 3,066,200 3 640,000 25 3,706,200 84.3 % Total commercial properties 57 18,008,904 26 12,115,348 83 30,124,252 91.8 % Residential: Manhattan Residential 3 (3) 472,105 12 2,656,856 15 3,128,961 87.6 % Suburban Residential — — — — — — — % Total residential properties 3 472,105 12 2,656,856 15 3,128,961 87.6 % Total portfolio 60 18,481,009 38 14,772,204 98 33,253,213 91.4 % (1) The weighted average occupancy for commercial properties represents the total occupied square feet divided by total square footage at acquisition. The weighted average occupancy for residential properties represents the total occupied units divided by total available units. (2) Includes the property at 600 Lexington Avenue in New York, New York which is classified as held for sale at December 31, 2017. (3) As of December 31, 2017 , we owned a building that was comprised of approximately 270,132 square feet (unaudited) of retail space and approximately 222,855 square feet (unaudited) of residential space. For the purpose of this report, we have included the building in the number of retail properties we own. However, we have included only the retail square footage in the retail approximate square footage, and have listed the balance of the square footage as residential square footage. (4) Includes the properties at 115-117 Stevens Avenue in Valhalla, New York, and 1-6 International Drive in Rye Brook, New York which are classified as held for sale at December 31, 2017. As of December 31, 2017 , we also managed an approximately 336,000 square foot (unaudited) office building owned by a third party and held debt and preferred equity investments with a book value of $2.3 billion , including $0.2 billion of debt and preferred equity investments and other financing receivables that are included in balance sheet line items other than the Debt and Preferred Equity Investments line item. Partnership Agreement In accordance with the partnership agreement of the Operating Partnership, or the Operating Partnership Agreement, we allocate all distributions and profits and losses in proportion to the percentage of ownership interests of the respective partners. As the managing general partner of the Operating Partnership, we are required to take such reasonable efforts, as determined by us in our sole discretion, to cause the Operating Partnership to distribute sufficient amounts to enable the payment of sufficient dividends by us to minimize any Federal income or excise tax at the Company level. Under the Operating Partnership Agreement, each limited partner has the right to redeem units of limited partnership interests for cash, or if we so elect, shares of our common stock on a one-for- one basis.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies Principles of Consolidation The consolidated financial statements include our accounts and those of our subsidiaries, which are wholly-owned or controlled by us. Entities which we do not control through our voting interest and entities which are variable interest entities, but where we are not the primary beneficiary, are accounted for under the equity method. See Note 5, "Debt and Preferred Equity Investments" and Note 6, "Investments in Unconsolidated Joint Ventures." All significant intercompany balances and transactions have been eliminated. We consolidate a variable interest entity, or VIE, in which we are considered the primary beneficiary. The primary beneficiary is the entity that has (i) the power to direct the activities that most significantly impact the entity's economic performance and (ii) the obligation to absorb losses of the VIE or the right to receive benefits from the VIE that could be significant to the VIE. A noncontrolling interest in a consolidated subsidiary is defined as the portion of the equity (net assets) in a subsidiary not attributable, directly or indirectly, to us. Noncontrolling interests are required to be presented as a separate component of equity in the consolidated balance sheet and the presentation of net income is modified to present earnings and other comprehensive income attributed to controlling and noncontrolling interests. We assess the accounting treatment for each joint venture and debt and preferred equity investment. This assessment includes a review of each joint venture or limited liability company agreement to determine the rights provided to each party and whether those rights are protective or participating. For all VIEs, we review such agreements in order to determine which party has the power to direct the activities that most significantly impact the entity's economic performance. In situations where we and our partner approve, among other things, the annual budget, receive a detailed monthly reporting package, meet on a quarterly basis to review the results of the joint venture, review and approve the joint venture's tax return before filing, and approve all leases that cover more than a nominal amount of space relative to the total rentable space at each property, we do not consolidate the joint venture as we consider these to be substantive participation rights that result in shared power of the activities that most significantly impact the performance of the joint venture. Our joint venture agreements typically contain certain protective rights such as requiring partner approval to sell, finance or refinance the property and the payment of capital expenditures and operating expenditures outside of the approved budget or operating plan. In January 2018, the partnership agreement for our investment in the property at 919 Third Avenue was modified resulting in our partner now having substantive participating rights in the venture. As a result the investment will no longer be deemed a VIE and our investment in the property will be deconsolidated as of January 1, 2018. The Company will record its non-controlling interest at fair value. This fair value will be allocated to the assets and liabilities, including identified intangibles. Under this methodology, the leases are ascribed an in-place lease intangible value as well as an above or below market lease intangible value which will be amortized over the remaining term of the associated leases. Investment in Commercial Real Estate Properties Real estate properties are presented at cost less accumulated depreciation and amortization. Costs directly related to the development or redevelopment of properties are capitalized. Ordinary repairs and maintenance are expensed as incurred; major replacements and betterments, which improve or extend the life of the asset, are capitalized and depreciated over their estimated useful lives. We recognize the assets acquired, liabilities assumed (including contingencies) and any noncontrolling interests in an acquired entity at their respective fair values on the acquisition date. When we acquire our partner's equity interest in an existing unconsolidated joint venture and gain control over the investment, we record the consolidated investment at fair value. The difference between the book value of our equity investment on the purchase date and our share of the fair value of the investment's purchase price is recorded as a purchase price fair value adjustment in our consolidated statements of operations. See Note 3, "Property Acquisitions." We allocate the purchase price of real estate to land and building (inclusive of tenant improvements) and, if determined to be material, intangibles, such as the value of above- and below-market leases and origination costs associated with the in-place leases. We depreciate the amount allocated to building (inclusive of tenant improvements) over their estimated useful lives, which generally range from three to 40 years. We amortize the amount allocated to the above- and below-market leases over the remaining term of the associated lease, which generally range from one to 14 years, and record it as either an increase (in the case of below-market leases) or a decrease (in the case of above-market leases) to rental income. We amortize the amount allocated to the values associated with in-place leases over the expected term of the associated lease, which generally ranges from one to 14 years. If a tenant vacates its space prior to the contractual termination of the lease and no rental payments are being made on the lease, any unamortized balance of the related intangible will be written off. The tenant improvements and origination costs are amortized as an expense over the remaining life of the lease (or charged against earnings if the lease is terminated prior to its contractual expiration date). We assess fair value of the leases based on estimated cash flow projections that utilize appropriate discount and capitalization rates and available market information. Estimates of future cash flows are based on a number of factors including the historical operating results, known trends, and market/economic conditions that may affect the property. To the extent acquired leases contain fixed rate renewal options that are below-market and determined to be material, we amortize such below-market lease value into rental income over the renewal period. As of December 31, 2017 , the weighted average amortization period for above-market leases, below-market leases, and in-place lease costs is 6.0 years, 23.3 years, and 16.3 years, respectively. We incur a variety of costs in the development and leasing of our properties. After the determination is made to capitalize a cost, it is allocated to the specific component of a project that is benefited. Determination of when a development project is substantially complete and capitalization must cease involves a degree of judgment. The costs of land and building under development include specifically identifiable costs. The capitalized costs include, but are not limited to, pre-construction costs essential to the development of the property, development costs, construction costs, interest costs, real estate taxes, salaries and related costs and other costs incurred during the period of development. We consider a construction project as substantially completed and held available for occupancy upon the completion of tenant improvements, but no later than one year after major construction activity ceases. We cease capitalization on the portions substantially completed and occupied or held available for occupancy, and capitalize only those costs associated with the portions under construction. Properties are depreciated using the straight-line method over the estimated useful lives of the assets. The estimated useful lives are as follows: Category Term Building (fee ownership) 40 years Building improvements shorter of remaining life of the building or useful life Building (leasehold interest) lesser of 40 years or remaining term of the lease Property under capital lease remaining lease term Furniture and fixtures four to seven years Tenant improvements shorter of remaining term of the lease or useful life Depreciation expense (including amortization of capital lease assets) totaled $365.3 million , $783.5 million , and $523.8 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. On a periodic basis, we assess whether there are any indications that the value of our real estate properties may be other than temporarily impaired or that their carrying value may not be recoverable. A property's value is considered impaired if management's estimate of the aggregate future cash flows (undiscounted) to be generated by the property is less than the carrying value of the property. To the extent impairment has occurred, the loss will be measured as the excess of the carrying amount of the property over the calculated fair value of the property. We also evaluate our real estate properties for impairment when a property has been classified as held for sale. Real estate assets held for sale are valued at the lower of their carrying value or fair value less costs to sell and depreciation expense is no longer recorded. See Note 4, "Properties Held for Sale and Dispositions." Cash and Cash Equivalents We consider all highly liquid investments with maturity of three months or less when purchased to be cash equivalents. Restricted Cash Restricted cash primarily consists of security deposits held on behalf of our tenants, interest reserves, as well as capital improvement and real estate tax escrows required under certain loan agreements. Fair Value Measurements See Note 16, "Fair Value Measurements." Investment in Marketable Securities At acquisition, we designate a security as held-to-maturity, available-for-sale, or trading. As of December 31, 2017 , we did not have any securities designated as held-to-maturity or trading. We account for our available-for-sale securities at fair value pursuant to Accounting Standards Codification, or ASC, 820-10, with the net unrealized gains or losses reported as a component of accumulated other comprehensive income or loss. Any unrealized losses that are determined to be other-than-temporary are recognized in earnings up to their credit component. The cost of bonds and marketable securities sold is determined using the specific identification method. At December 31, 2017 and 2016 , we held the following marketable securities (in thousands): December 31, 2017 2016 Equity marketable securities $ — $ 48,315 Commercial mortgage-backed securities 28,579 36,795 Total marketable securities available-for-sale $ 28,579 $ 85,110 The cost basis of the commercial mortgage-backed securities was $27.5 million and $36.0 million at December 31, 2017 and 2016 , respectively. These securities mature at various times through 2035. We held no equity marketable securities as of December 31, 2017 . The cost basis of the equity marketable securities was $43.3 million at December 31, 2016 . During the year ended December 31, 2017 , we disposed of marketable securities for aggregate net proceeds of $55.1 million and realized a gain of $3.3 million , which is included in gain (loss) on sale of investment in marketable securities on the consolidated statements of operations. During the year ended December 31, 2016 , we disposed of marketable securities for aggregate net proceeds of $7.0 million and realized a loss of $0.1 million , which is included in gain (loss) on sale of investment in marketable securities on the consolidated statements of operations. Investments in Unconsolidated Joint Ventures We account for our investments in unconsolidated joint ventures under the equity method of accounting in cases where we exercise significant influence over, but do not control, these entities and are not considered to be the primary beneficiary. We consolidate those joint ventures that we control or which are VIEs and where we are considered to be the primary beneficiary. In all these joint ventures, the rights of the joint venture partner are both protective as well as participating. Unless we are determined to be the primary beneficiary in a VIE, these participating rights preclude us from consolidating these VIE entities. These investments are recorded initially at cost, as investments in unconsolidated joint ventures, and subsequently adjusted for equity in net income (loss) and cash contributions and distributions. Equity in net income (loss) from unconsolidated joint ventures is allocated based on our ownership or economic interest in each joint venture. When a capital event (as defined in each joint venture agreement) such as a refinancing occurs, if return thresholds are met, future equity income will be allocated at our increased economic interest. We recognize incentive income from unconsolidated real estate joint ventures as income to the extent it is earned and not subject to a clawback feature. Distributions we receive from unconsolidated real estate joint ventures in excess of our basis in the investment are recorded as offsets to our investment balance if we remain liable for future obligations of the joint venture or may otherwise be committed to provide future additional financial support. None of the joint venture debt is recourse to us. The Company has performance guarantees under master leases at two joint ventures. See Note 6, "Investments in Unconsolidated Joint Ventures." We assess our investments in unconsolidated joint ventures for recoverability, and if it is determined that a loss in value of the investment is other than temporary, we write down the investment to its fair value. We evaluate our equity investments for impairment based on the joint ventures' projected discounted cash flows. We do not believe that the values of any of our equity investments were impaired at December 31, 2017 . We may originate loans for real estate acquisition, development and construction, where we expect to receive some of the residual profit from such projects. When the risk and rewards of these arrangements are essentially the same as an investor or joint venture partner, we account for these arrangements as real estate investments under the equity method of accounting for investments. Otherwise, we account for these arrangements consistent with the accounting for our debt and preferred equity investments. Deferred Lease Costs Deferred lease costs consist of fees and direct costs incurred to execute operating leases and are amortized on a straight-line basis over the related lease term. Certain of our employees provide leasing services to the wholly-owned properties. For the years ended December 31, 2017 , 2016 and 2015 , $16.4 million , $15.4 million , and $15.4 million of their compensation, respectively, was capitalized and is amortized over an estimated average lease term of seven years. Deferred Financing Costs Deferred financing costs represent commitment fees, legal, title and other third party costs associated with obtaining commitments for financing which result in a closing of such financing. These costs are amortized over the terms of the respective agreements. Unamortized deferred financing costs are expensed when the associated debt is refinanced or repaid before maturity. Costs incurred in seeking financing transactions, which do not close, are expensed in the period in which it is determined that the financing will not close. Deferred debt issuance costs related to a recognized debt liability are presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. Revenue Recognition Rental revenue is recognized on a straight-line basis over the term of the lease. Rental revenue recognition commences when the tenant takes possession or controls the physical use of the leased space. In order for the tenant to take possession, the leased space must be substantially ready for its intended use. To determine whether the leased space is substantially ready for its intended use, management evaluates whether we are or the tenant is the owner of tenant improvements for accounting purposes. When management concludes that we are the owner of tenant improvements, rental revenue recognition begins when the tenant takes possession of the finished space, which is when such tenant improvements are substantially complete. In certain instances, when management concludes that we are not the owner (the tenant is the owner) of tenant improvements, rental revenue recognition begins when the tenant takes possession of or controls the space. When management concludes that we are the owner of tenant improvements for accounting purposes, we record amounts funded to construct the tenant improvements as a capital asset. For these tenant improvements, we record amounts reimbursed by tenants as a reduction of the capital asset. When management concludes that the tenant is the owner of tenant improvements for accounting purposes, we record our contribution towards those improvements as a lease incentive, which is included in deferred costs, net on our consolidated balance sheets and amortized as a reduction to rental revenue on a straight-line basis over the term of the lease. The excess of rents recognized over amounts contractually due pursuant to the underlying leases are included in deferred rents receivable on the consolidated balance sheets. We establish, on a current basis, an allowance for future potential tenant credit losses, which may occur against this account. The balance reflected on the consolidated balance sheets is net of such allowance. In addition to base rent, our tenants also generally will pay their pro rata share of increases in real estate taxes and operating expenses for the building over a base year. In some leases, in lieu of paying additional rent based upon increases in building operating expenses, the tenant will pay additional rent based upon increases in the wage rate paid to porters over the porters' wage rate in effect during a base year or increases in the consumer price index over the index value in effect during a base year. In addition, many of our leases contain fixed percentage increases over the base rent to cover escalations. Electricity is most often supplied by the landlord either on a sub-metered basis, or rent inclusion basis (i.e., a fixed fee is included in the rent for electricity, which amount may increase based upon increases in electricity rates or increases in electrical usage by the tenant). Base building services other than electricity (such as heat, air conditioning and freight elevator service during business hours, and base building cleaning) are typically provided at no additional cost, with the tenant paying additional rent only for services which exceed base building services or for services which are provided outside normal business hours. These escalations are based on actual expenses incurred in the prior calendar year. If the expenses in the current year are different from those in the prior year, then during the current year, the escalations will be adjusted to reflect the actual expenses for the current year. We recognized $20.3 million , $196.2 million , and $38.7 million of rental revenue for the years ended December 31, 2017 , 2016 , and 2015 respectively, for the amortization of aggregate below-market leases in excess of above-market leases and a reduction in lease origination costs, resulting from the allocation of the purchase price of the applicable properties. Included in rental revenue for the year ended December 31, 2016 is $172.4 million related to the amortization of below-market leases at 388-390 Greenwich Street as a result of the tenant exercising their option to purchase the property and entering into an agreement to accelerate the sale. We recognized as a reduction to interest expense the amortization of the above-market rate mortgages assumed of $0.8 million , $2.8 million , and $2.3 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. The following summarizes our identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases) as of December 31, 2017 and 2016 (in thousands): December 31, 2017 2016 Identified intangible assets (included in other assets): Gross amount $ 325,880 $ 651,099 Accumulated amortization (277,038 ) (410,930 ) Net (1) $ 48,842 $ 240,169 Identified intangible liabilities (included in deferred revenue): Gross amount $ 540,283 $ 655,930 Accumulated amortization (402,583 ) (464,749 ) Net (1) $ 137,700 $ 191,181 (1) As of December 31, 2017 , $13.9 million net intangible assets and $4.1 million net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale. The estimated annual amortization of acquired above-market leases, net of acquired (below-market) leases (a component of rental revenue), for each of the five succeeding years is as follows (in thousands): 2018 $ (13,853 ) 2019 (13,250 ) 2020 (12,432 ) 2021 (3,950 ) 2022 (3,647 ) The estimated annual amortization of all other identifiable assets (a component of depreciation and amortization expense) including tenant improvements for each of the five succeeding years is as follows (in thousands): 2018 $ 9,700 2019 7,716 2020 6,783 2021 3,927 2022 2,365 We record a gain on sale of real estate when title is conveyed to the buyer, subject to the buyer's financial commitment being sufficient to provide economic substance to the sale and provided that we have no substantial economic involvement with the buyer. Interest income on debt and preferred equity investments is accrued based on the contractual terms of the instruments and when, in the opinion of management, it is deemed collectible. Some debt and preferred equity investments provide for accrual of interest at specified rates, which differ from current payment terms. Interest is recognized on such loans at the accrual rate subject to management's determination that accrued interest is ultimately collectible, based on the underlying collateral and operations of the borrower. If management cannot make this determination, interest income above the current pay rate is recognized only upon actual receipt. Deferred origination fees, original issue discounts and loan origination costs, if any, are recognized as an adjustment to interest income over the terms of the related investments using the effective interest method. Fees received in connection with loan commitments are also deferred until the loan is funded and are then recognized over the term of the loan as an adjustment to yield. Discounts or premiums associated with the purchase of loans are amortized or accreted into interest income as a yield adjustment on the effective interest method based on expected cash flows through the expected maturity date of the related investment. If we purchase a debt or preferred equity investment at a discount, intend to hold it until maturity and expect to recover the full value of the investment, we accrete the discount into income as an adjustment to yield over the term of the investment. If we purchase a debt or preferred equity investment at a discount with the intention of foreclosing on the collateral, we do not accrete the discount. For debt investments acquired at a discount for credit quality, the difference between contractual cash flows and expected cash flows at acquisition is not accreted. Anticipated exit fees, the collection of which is expected, are also recognized over the term of the loan as an adjustment to yield. Debt and preferred equity investments are placed on a non-accrual status at the earlier of the date at which payments become 90 days past due or when, in the opinion of management, a full recovery of interest income becomes doubtful. Interest income recognition on any non-accrual debt or preferred equity investment is resumed when such non-accrual debt or preferred equity investment becomes contractually current and performance is demonstrated to be resumed. Interest is recorded as income on impaired loans only to the extent cash is received. We may syndicate a portion of the loans that we originate or sell the loans individually. When a transaction meets the criteria for sale accounting, we derecognize the loan sold and recognize gain or loss based on the difference between the sales price and the carrying value of the loan sold. Any related unamortized deferred origination fees, original issue discounts, loan origination costs, discounts or premiums at the time of sale are recognized as an adjustment to the gain or loss on sale, which is included in investment income on the consolidated statement of operations. Any fees received at the time of sale or syndication are recognized as part of investment income. Asset management fees are recognized on a straight-line basis over the term of the asset management agreement. Allowance for Doubtful Accounts We maintain an allowance for doubtful accounts for estimated losses resulting from the inability of our tenants to make required payments. If the financial condition of a specific tenant were to deteriorate, resulting in an impairment of its ability to make payments, additional allowances may be required. Reserve for Possible Credit Losses The expense for possible credit losses in connection with debt and preferred equity investments is the charge to earnings to increase the allowance for possible credit losses to the level that we estimate to be adequate, based on Level 3 data, considering delinquencies, loss experience and collateral quality. Other factors considered include geographic trends, product diversification, the size of the portfolio and current economic conditions. Based upon these factors, we establish a provision for possible credit loss on each individual investment. When it is probable that we will be unable to collect all amounts contractually due, the investment is considered impaired. Where impairment is indicated on an investment that is held to maturity, a valuation allowance is measured based upon the excess of the recorded investment amount over the fair value of the collateral. Any deficiency between the carrying amount of an asset and the calculated value of the collateral is charged to expense. We continue to assess or adjust our estimates based on circumstances of a loan and the underlying collateral. If additional information reflects increased recovery of our investment, we will adjust our reserves accordingly. There were no loan reserves recorded during the years ended December 31, 2017 , 2016 , and 2015 . Debt and preferred equity investments held for sale are carried at the lower of cost or fair market value using available market information obtained through consultation with dealers or other originators of such investments as well as discounted cash flow models based on Level 3 data pursuant to ASC 820-10. As circumstances change, management may conclude not to sell an investment designated as held for sale. In such situations, the investment will be reclassified at its net carrying value to debt and preferred equity investments held to maturity. For these reclassified investments, the difference between the current carrying value and the expected cash to be collected at maturity will be accreted into income over the remaining term of the investment. Rent Expense Rent expense is recognized on a straight-line basis over the initial term of the lease. The excess of the rent expense recognized over the amounts contractually due pursuant to the underlying lease is included in the deferred lease payable on the consolidated balance sheets. Underwriting Commissions and Costs Underwriting commissions and costs incurred in connection with our stock offerings are reflected as a reduction of additional paid-in-capital. Exchangeable Debt Instruments The initial proceeds from exchangeable debt that may be settled in cash, including partial cash settlements, are bifurcated between a liability component and an equity component associated with the embedded conversion option. The objective of the accounting guidance is to require the liability and equity components of exchangeable debt to be separately accounted for in a manner such that the interest expense on the exchangeable debt is not recorded at the stated rate of interest but rather at an effective rate that reflects the issuer's conventional debt borrowing rate at the date of issuance. We calculate the liability component of exchangeable debt based on the present value of the contractual cash flows discounted at our comparable market conventional debt borrowing rate at the date of issuance. The difference between the principal amount and the fair value of the liability component is reported as a discount on the exchangeable debt that is accreted as additional interest expense from the issuance date through the contractual maturity date using the effective interest method. A portion of this additional interest expense may be capitalized to the development and redevelopment balances qualifying for interest capitalization each period. The liability component of the exchangeable debt is reported net of discounts on our consolidated balance sheets. We calculate the equity component of exchangeable debt based on the difference between the initial proceeds received from the issuance of the exchangeable debt and the fair value of the liability component at the issuance date. The equity component is included in additional paid-in-capital, net of issuance costs, on our consolidated balance sheets. We allocate issuance costs for exchangeable debt between the liability and the equity components based on their relative values. Transaction Costs In January 2017, we adopted ASU No. 2017-01, Business Combinations: Clarifying the Definition of a Business, which changed how we account for transaction costs. Prior to January 2017, transaction costs were expensed as incurred. Starting in January 2017, transaction costs for asset acquisitions are capitalized to the investment basis which is then subject to a purchase price allocation based on relative fair value and transaction costs for business combinations or costs incurred on potential transactions which are not consummated are expensed as incurred. Income Taxes SL Green is taxed as a REIT under Section 856(c) of the Code. As a REIT, SL Green generally is not subject to Federal income tax. To maintain its qualification as a REIT, SL Green must distribute at least 90% of its REIT taxable income to its stockholders and meet certain other requirements. If SL Green fails to qualify as a REIT in any taxable year, SL Green will be subject to Federal income tax on its taxable income at regular corporate rates. SL Green may also be subject to certain state, local and franchise taxes. Under certain circumstances, Federal income and excise taxes may be due on its undistributed taxable income. The Operating Partnership is a partnership and, as a result, all income and losses of the partnership are allocated to the partners for inclusion in their respective income tax returns. The only provision for income taxes included in the consolidated statements of operations relates to the Operating Partnership’s consolidated taxable REIT subsidiaries. The Operating Partnership may also be subject to certain state, local and franchise taxes. Pursuant to amendments to the Code that became effective January 1, 2001, we have elected, and may elect in the future, to treat certain of our existing or newly created corporate subsidiaries as taxable REIT subsidiaries, or TRSs. In general, TRSs may perform non-customary services for the tenants of the Company, hold assets that we cannot hold directly and generally may engage in any real estate or non-real estate related business. The TRSs generate income, resulting in Federal and state income tax liability for these entities. During the years ended December 31, 2017 , 2016 and 2015 , we recorded Federal, state and local tax provisions of $4.3 million , $2.8 million , and $3.1 million , respectively. For the year ended December 31, 2017, the Company paid distributions on its common stock of $3.10 per share which represented $1.24 per share of ordinary income and $1.86 per share of capital gains. For the year ended December 31, 2016, the Company paid distributions on its common stock of $2.88 per share which represented $2.48 per share of ordinary income, and $0.40 per share of capital gains. For the year ended December 31,

Property Acquisitions

Property Acquisitions	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Property Acquisitions	Property Acquisitions 2017 Acquisitions During the year ended December 31, 2017 , we did not acquire any properties from a third party. 2016 Acquisitions During the year ended December 31, 2016, the property listed below was acquired from a third party. The following summarizes our final allocation of the purchase price of the assets acquired and liabilities assumed upon the closing of this acquisition (in thousands): 183 Broadway Acquisition Date March 2016 Ownership Type Fee Interest Property Type Retail/Residential Purchase Price Allocation: Land $ 5,799 Building and building leasehold 23,431 Above-market lease value — Acquired in-place leases 773 Other assets, net of other liabilities 20 Assets acquired 30,023 Mark-to-market assumed debt — Below-market lease value (1,523 ) Derivatives — Liabilities assumed (1,523 ) Purchase price $ 28,500 Net consideration funded by us at closing, excluding consideration financed by debt $ 28,500 Equity and/or debt investment held $ — Debt assumed $ — 2015 Acquisitions During the year ended December 31, 2016, we finalized the purchase price allocations for the following 2015 acquisitions based on facts and circumstances that existed at the acquisition date for each property (in thousands): 600 Lexington Avenue (1)(2) 187 Broadway and 5 & 7 Dey Street (1)(3) 11 Madison Avenue (1) 110 Greene Street (1)(4) Upper East Side Residential (1)(5) 1640 Flatbush Avenue (1) Acquisition Date December 2015 August 2015 August 2015 July 2015 June 2015 March 2015 Ownership Type Fee Interest Fee Interest Fee Interest Fee Interest Fee Interest Fee Interest Property Type Office Residential/Retail Office Office Residential/Retail Retail Purchase Price Allocation: Land $ 81,670 $ 20,266 $ 675,776 $ 45,120 $ 48,152 $ 6,226 Building and building leasehold 182,447 42,468 1,553,602 215,470 — 501 Above-market lease value 3,320 17 19,764 — — — Acquired in-place leases 22,449 3,621 366,949 8,967 1,922 146 Other assets, net of other liabilities — — — — — — Assets acquired 289,886 66,372 2,616,091 269,557 50,074 6,873 Mark-to-market assumed debt (55 ) — — — — — Below-market lease value (5,831 ) (3,226 ) (187,732 ) (14,557 ) — (73 ) Derivatives — — — — — — Liabilities assumed (5,886 ) (3,226 ) (187,732 ) (14,557 ) — (73 ) Purchase price $ 284,000 $ 63,146 $ 2,428,359 $ 255,000 $ 50,074 $ 6,800 Net consideration funded by us at closing, excluding consideration financed by debt $ 79,085 $ — $ — $ — $ — $ — Equity and/or debt investment held $ 54,575 $ — $ — $ — $ — $ — Debt assumed $ 112,795 $ — $ — $ — $ — $ — (1) Based on our preliminary analysis of the purchase price, we had allocated $97.0 million and $180.2 million to land and building, respectively, at 600 Lexington Avenue, $22.1 million and $41.0 million to land and building, respectively, at 187 Broadway and 5&7 Dey Street, $849.9 million and $1.6 billion to land and building, respectively, at 11 Madison Avenue, $89.3 million and $165.8 million to land and building, respectively, at 110 Greene Street, and $17.5 million and $32.5 million to land and building, respectively, at the Upper Eastside Residential Property and $6.1 million and $0.7 million to land and building, respectively, at 1640 Flatbush Avenue. The impact to our consolidated statements of operations for the twelve months ended December 31, 2015 was an increase in rental revenue of $7.8 million for the amortization of aggregate below-market leases and an additional $18.5 million of depreciation expense. (2) In December 2015, we acquired Canada Pension Plan Investment Board's 45% interest in this property, thereby consolidating full ownership of the property. The transaction valued the consolidated interests at $277.3 million . We recognized a purchase price fair value adjustment of $40.1 million upon closing of this transaction. This property, which we initially acquired in May 2010, was previously accounted for as an investment in unconsolidated joint ventures. (3) We acquired this property for consideration that included the issuance of $10.0 million and $26.9 million aggregate liquidation preferences of Series R and S Preferred Units, respectively, of limited partnership interest of the Operating Partnership and cash. (4) We acquired a 90.0% controlling interest in this property for consideration that included the issuance of $5.0 million and $6.7 million aggregate liquidation preferences of Series P and Q Preferred Units, respectively, of limited partnership interest of the Operating Partnership and cash. (5) We, along with our joint venture partner, acquired this property for consideration that included the issuance of $13.8 million aggregate liquidation preference of Series N Preferred Units of limited partnership interest of the Operating Partnership and cash. We hold a 95.1% controlling interest in this joint venture. For business combinations achieved in stages, the acquisition-date fair value of our equity interest in a property immediately before the acquisition date is determined based on estimated cash flow projections that utilize available market information and discount and capitalization rates that we deem appropriate. Estimates of future cash flows are based on a number of factors including historical operating results, known and anticipated trends, and market and economic conditions. The acquisition-date fair value of the equity interest in 600 Lexington Avenue, which was acquired in 2015, immediately before the acquisition date and the resulting purchase price fair value adjustment, as determined in accordance with the methodology set out in the prior sentence, are as follows (in thousands): 600 Lexington Avenue Contract purchase price $ 284,000 Net consideration funded by us at closing, excluding consideration financed by debt (79,085 ) Debt assumed (112,795 ) Fair value of retained equity interest 92,120 Equity and/or debt investment held (54,575 ) Other (1) 2,533 Purchase price fair value adjustment $ 40,078 (1) Includes the acceleration of a deferred leasing commission from the joint venture to the Company. Pro Forma Unaudited The following table summarizes, on an unaudited pro forma basis, the results of operations of 11 Madison Avenue, which are included in the consolidated results of operations for year ended December 31, 2015 as though the acquisition of 11 Madison Avenue was completed on January 1, 2015. The supplemental pro forma data is not necessarily indicative of what the actual results of operations would have been assuming the transactions had been completed as set forth above, nor do they purport to represent our results of operations for future periods. (in thousands, except per share/unit amounts) Actual revenues since acquisition $ 29,865 Actual net income since acquisition 159 Pro forma revenues 1,657,937 Pro forma income from continuing operations (1) 102,440 Pro forma basic earnings per share $ 0.76 Pro forma diluted earnings per share $ 0.75 Pro forma basic earnings per unit $ 0.76 Pro forma diluted earnings per unit $ 0.75 (1) The pro forma income from continuing operations for the year ended December 31, 2015 includes the effect of the incremental borrowings, including a $ 1.4 billion , 10 -year, interest only, fixed rate mortgage financing carrying a per annum stated interest rate of 3.838% to complete the acquisition and the preliminary allocation of purchase price.

Properties Held for Sale and Pr

Properties Held for Sale and Property Dispositions	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Properties Held for Sale and Property Dispositions	Properties Held for Sale and Property Dispositions Properties Held for Sale As of December 31, 2017 , 600 Lexington Avenue in Manhattan, 115-117 Stevens Avenue in Valhalla, New York, and 1-6 International Drive in Rye Brook, New York were classified as held for sale. During the fourth quarter of 2017, we entered into an agreement to sell the property at 600 Lexington Avenue for a gross asset valuation of $305.0 million . We closed on the sale of 600 Lexington Avenue in January 2018. During the fourth quarter of 2017, the Company recorded a charge of $17.8 million in connection with the reclassification of 115-117 Stevens Avenue to held for sale, and a charge of $69.1 million in connection with the reclassification of 1-6 International Drive to held for sale. These charges are included in depreciable real estate reserves in the consolidated statement of operations. The Company classified 16 Court Street in Brooklyn, New York and 125 Chubb Way in Lyndhurst, New Jersey as held for sale as of September 30, 2017; 125 Chubb Way in Lyndhurst, New Jersey and the properties at 680-750 Washington Boulevard in Stamford, Connecticut as held for sale as of June 30, 2017; and 520 White Plains Road in Tarrytown, NY and a 90% interest in 102 Greene Street in New York, NY as held for sale as of March 31, 2017. Property Dispositions The following table summarizes the properties sold during the years ended December 31, 2017 , 2016 , and 2015 : Property Disposition Date Property Type (unaudited) Approximate Usable Square Feet Sales Price (1) (in millions) Gain (Loss) on Sale (2) (in millions) 1515 Broadway (3) December 2017 Office 1,750,000 $ 1,950.0 $ — 125 Chubb Way (4) October 2017 Office 278,000 29.5 (26.1 ) 16 Court Street October 2017 Office 317,600 171.0 64.9 680-750 Washington Boulevard (5) July 2017 Office 325,000 97.0 (44.2 ) 520 White Plains Road (6) April 2017 Office 180,000 21.0 (14.6 ) 102 Greene Street (7) April 2017 Retail 9,200 43.5 4.9 400 East 57th Street October 2016 Residential 290,482 83.3 23.9 11 Madison Avenue (8) August 2016 Office 2,314,000 2,605.0 3.6 500 West Putnam (9) July 2016 Office 121,500 41.0 (10.4 ) 388 Greenwich June 2016 Office 2,635,000 2,002.3 206.5 7 International Drive May 2016 Land 31 Acres 20.0 (6.9 ) 248-252 Bedford Avenue February 2016 Residential 66,611 55.0 15.3 885 Third Avenue (10) February 2016 Land 607,000 453.0 (8.8 ) 140-150 Grand Street (11) December 2015 Office/Development 215,100 32.0 (20.1 ) 570 & 574 Fifth Avenue December 2015 Development 24,327 125.4 24.6 120 West 45th Street September 2015 Office 440,000 365.0 58.6 131-137 Spring Street (12) August 2015 Office 68,342 277.8 101.1 180 Maiden Lane January 2015 Office 1,090,000 470.0 17.0 (1) Sales price represents the actual sales price for an entire property or the gross asset valuation for interests in a property. (2) The gain on sale for 16 Court Street, 102 Greene Street, 400 East 57th Street, 11 Madison Avenue, 388 Greenwich, 248-252 Bedford Avenue, 570 & 574 Fifth Avenue, 120 West 45th Street, 131-137 Spring Street, and 180 Maiden Lane are net of $2.5 million , $0.9 million , $1.0 million , $0.6 million , $1.6 million , $1.3 million , $4.0 million , $2.0 million , $4.1 million , and $0.8 million in employee compensation accrued in connection with the realization of these investment gains. Additionally, amounts do not include adjustments for expenses recorded in subsequent periods. (3) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. See Note 6, "Investments in Unconsolidated Joint Ventures." (4) The Company recorded a $26.1 million charge in 2017 that is included in depreciable real estate reserves in the consolidated statement of operations. (5) The Company recorded a $44.2 million charge in 2017 that is included in depreciable real estate reserves in the consolidated statement of operations. (6) The Company recorded a $14.6 million charge in 2017 that is included in depreciable real estate reserves in the consolidated statement of operations. (7) In April 2017, we closed on the sale of a 90% interest 102 Greene Street and had subsequently accounted for our interest in the property as an investment in unconsolidated joint ventures. We sold the remaining 10% interest in September 2017. See Note 6, "Investments in Unconsolidated Joint Ventures." (8) In August 2016, we sold a 40% interest in 11 Madison Avenue. The sale did not meet the criteria for sale accounting and, as a result, the property was accounted for under the profit sharing method. In November 2016, the Company obtained consent to the modifications to the mortgage on the property, which resulted in the Company achieving sale accounting on the transaction. See Note 6, "Investments in Unconsolidated Joint Ventures." (9) The Company recorded a $10.4 million charge in 2016 that is included in depreciable real estate reserves in the consolidated statement of operations (10) In February 2016, we closed on the sale of 885 Third Avenue. The sale did not meet the criteria for sale accounting and as a result the property remained on our consolidated financial statements until the criteria was met in April 2017. (11) The Company recorded a $19.2 million charge in 2015 that is included in depreciable real estate reserves in the consolidated statement of operations. (12) We sold an 80% interest in 131-137 Spring Street and have subsequently accounted for our interest in the properties as an investment in unconsolidated joint ventures. See Note 6, "Investments in Unconsolidated Joint Ventures." Discontinued Operations The Company adopted ASU 2014-08 effective January 1, 2015 which raised the threshold for disposals to qualify as discontinued operations to include only dispositions that represent a strategic shift in an entity’s operations. The guidance was applied prospectively for new disposals. Since adoption no disposals have been deemed to represent strategic shifts in the Company's operations and as a result, the results of operations of all disposals are included in continuing operations for all periods presented. Discontinued operations includes the results of operations of 180 Maiden Lane which was held for sale at December 31, 2014 and sold in January 2015. The following table summarizes net income from discontinued operations for the years ended December 31, 2017 , 2016 , and 2015 respectively (in thousands): Year Ended December 31, 2017 2016 2015 Revenues Rental revenue $ — $ — $ 236 Escalation and reimbursement revenues — — (127 ) Other income — — — Total revenues — — 109 Operating expenses — — (631 ) Real estate taxes — — 250 Ground rent — — — Transaction related costs — — (49 ) Interest expense, net of interest income — — 109 Amortization of deferred financing costs — — 3 Depreciation and amortization — — — Total expenses — — (318 ) Net income from discontinued operations $ — $ — $ 427

Debt and Preferred Equity Inves

Debt and Preferred Equity Investments	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Debt and Preferred Equity Investments	Debt and Preferred Equity Investments Below is the rollforward analysis of the activity relating to our debt and preferred equity investments as of December 31, 2017 and 2016 (in thousands): December 31, 2017 December 31, 2016 Balance at beginning of period (1) $ 1,640,412 $ 1,670,020 Debt investment originations/accretion (2) 1,142,591 1,009,176 Preferred Equity investment originations/accretion (2) 144,456 5,698 Redemptions/sales/syndications/amortization (3) (813,418 ) (1,044,482 ) Balance at end of period (1) $ 2,114,041 $ 1,640,412 (1) Net of unamortized fees, discounts, and premiums. (2) Accretion includes amortization of fees and discounts and paid-in-kind investment income. (3) Certain participations in debt investments that were sold or syndicated did not meet the conditions for sale accounting are included in other assets and other liabilities on the consolidated balance sheets. Debt Investments As of December 31, 2017 and 2016 , we held the following debt investments with an aggregate weighted average current yield of 9.31% , excluding our investment in Two Herald Square, at December 31, 2017 (in thousands): Loan Type December 31, 2017 Future Funding Obligations December 31, 2017 Senior Financing December 31, 2017 Carrying Value (1) December 31, 2016 Carrying Value (1) Maturity Date (2) Fixed Rate Investments: Mortgage/Jr. Mortgage Loan (3) $ — $ — $ 250,464 $ — April 2017 Mortgage Loan (4) — — 26,366 26,311 February 2019 Mortgage Loan — — 239 380 August 2019 Mezzanine Loan (5a) — 1,160,000 204,005 — March 2020 Mezzanine Loan — 15,000 3,500 3,500 September 2021 Mezzanine Loan — 147,000 24,913 — April 2022 Mezzanine Loan — 86,976 12,699 12,692 November 2023 Mezzanine Loan (5b) — 115,000 12,932 12,925 June 2024 Mezzanine Loan — 95,000 30,000 30,000 January 2025 Mezzanine Loan — 340,000 15,000 15,000 November 2026 Mezzanine Loan — 1,657,500 55,250 — June 2027 Mezzanine Loan (6) — — — 66,129 Jr. Mortgage Participation/Mezzanine Loan (7) — — — 193,422 Total fixed rate $ — $ 3,616,476 $ 635,368 $ 360,359 Floating Rate Investments: Mezzanine Loan (5c)(8) $ 795 $ — $ 15,148 $ 15,051 March 2018 Mezzanine Loan — 40,000 19,982 19,913 April 2018 Jr. Mortgage Participation — 94,546 34,947 34,844 April 2018 Mezzanine Loan 523 20,523 10,934 10,863 August 2018 Mortgage/Mezzanine Loan — — 19,940 19,840 August 2018 Mortgage Loan — 65,000 14,955 14,880 August 2018 Mortgage/Mezzanine Loan (9) — — 16,969 16,960 September 2018 Mezzanine Loan — 37,500 14,855 14,648 September 2018 Mortgage/Mezzanine Loan (10) 391 — 23,609 20,423 October 2018 Mezzanine Loan 2,325 45,025 34,879 34,502 October 2018 Mezzanine Loan — 335,000 74,755 74,476 November 2018 Mezzanine Loan (5d)(8) — 85,000 15,381 15,141 December 2018 Mezzanine Loan (5e)(8) — 65,000 14,869 14,656 December 2018 Mezzanine Loan — 33,000 26,927 26,850 December 2018 Mezzanine Loan — 175,000 59,723 56,114 December 2018 Mezzanine Loan — 45,000 12,174 12,104 January 2019 Mortgage/Mezzanine Loan (5f) 26,284 — 162,553 — January 2019 Mezzanine Loan 5,372 25,289 8,550 5,410 January 2019 Mezzanine Loan — 38,000 21,939 21,891 March 2019 Mezzanine Loan 11 174,947 37,250 — April 2019 Mezzanine Loan — 265,000 24,830 24,707 April 2019 Mortgage/Jr. Mortgage Participation Loan 27,617 199,733 71,832 65,554 August 2019 Loan Type December 31, 2017 Future Funding Obligations December 31, 2017 Senior Financing December 31, 2017 Carrying Value (1) December 31, 2016 Carrying Value (1) Maturity Date (2) Mezzanine Loan 2,034 189,829 37,851 37,322 September 2019 Mortgage/Mezzanine Loan 36,391 — 143,919 111,819 September 2019 Mezzanine Loan — 350,000 34,737 — October 2019 Mortgage/Mezzanine Loan 25,643 — 43,845 33,682 January 2020 Mezzanine Loan (11) 3,621 555,379 75,834 125,911 January 2020 Mezzanine Loan 6,913 34,337 11,259 — July 2020 Mezzanine Loan (12) 51,494 310,654 75,428 63,137 November 2020 Mortgage and Mezzanine Loan 42,510 — 88,989 — December 2020 Mortgage and Mezzanine Loan — — 35,152 — December 2020 Jr. Mortgage Participation/Mezzanine Loan — 60,000 15,635 15,606 July 2021 Mezzanine Loan — 280,000 34,600 — August 2022 Mortgage/Mezzanine Loan (13) — — — 29,998 Mezzanine Loan (14) — — — 64,505 Mezzanine Loan (15) — — — 15,369 Mortgage/Mezzanine Loan (6) — — — 32,847 Mortgage/Mezzanine Loan (6) — — — 22,959 Mezzanine Loan (16) — — — 14,957 Mortgage/Mezzanine Loan (17) — — — 145,239 Total floating rate $ 231,924 $ 3,523,762 $ 1,334,250 $ 1,232,178 Total $ 231,924 $ 7,140,238 $ 1,969,618 $ 1,592,537 (1) Carrying value is net of discounts, premiums, original issue discounts and deferred origination fees. (2) Represents contractual maturity, excluding any unexercised extension options. (3) These loans were purchased at par in April and May 2017 and were in maturity default at the time of acquisition. At the time the loans were purchased, the Company expected to collect all contractually required payments, including interest. In August 2017, the Company determined that it was probable that the loans would not be repaid in full and therefore, the loans were put on non-accrual status. No impairment was recorded as the Company believes that the fair value of the property exceeds the carrying amount of the loans. The loans had an outstanding balance, including accrued interest, of $259.3 million at the time that they were put on non-accrual status. (4) In September 2014, we acquired a $26.4 million mortgage loan at a $0.2 million discount and a $5.7 million junior mortgage participation at a $5.7 million discount. The junior mortgage participation was a nonperforming loan at acquisition, is currently on non-accrual status and has no carrying value. (5) Carrying value is net of the following amounts that were sold or syndicated, which are included in other assets and other liabilities on the consolidated balance sheets as a result of the transfers not meeting the conditions for sale accounting: (a) $1.2 million , (b) $12.0 million , (c) $5.1 million (d) $14.6 million , (e) $14.1 million , and (f) $21.2 million . (6) This loan was repaid in June 2017. (7) This loan was repaid in March 2017. (8) This loan was extended in December 2017. (9) This loan was extended in August 2017. (10) This loan was extended in September 2017. (11) $66.1 million of outstanding principal was syndicated in February 2017. (12) This loan was extended in November 2017. (13) This loan was repaid in December 2017. (14) This loan was repaid in November 2017. (15) This loan was repaid in September 2017. (16) This loan was contributed to a joint venture in May 2017. (17) This loan was repaid in January 2017. Preferred Equity Investments As of December 31, 2017 and 2016 , we held the following preferred equity investments with an aggregate weighted average current yield of 6.99% at December 31, 2017 (in thousands): Type December 31, 2017 Future Funding Obligations December 31, 2017 December 31, 2017 (1) December 31, 2016 (1) Mandatory Redemption (2) Preferred Equity (3) $ — $ 272,000 $ 144,423 $ — April 2021 Preferred Equity (4) — — — 9,982 Preferred Equity (5) — — — 37,893 $ — $ 272,000 $ 144,423 $ 47,875 (1) Carrying value is net of deferred origination fees. (2) Represents contractual maturity, excluding any unexercised extension options. (3) In February 2016, we closed on the sale of 885 Third Avenue and retained a preferred equity position in the property. The sale did not meet the criteria for sale accounting under the full accrual method in ASC 360-20, Property, Plant and Equipment - Real Estate Sales. As a result the property remained on our consolidated balance sheet until the criteria was met in April 2017 at which time the property was deconsolidated and the preferred equity investment was recognized. (4) This investment was redeemed in May 2017. (5) This investment was redeemed in April 2017. The following table is a rollforward of our total loan loss reserves at December 31, 2017 , 2016 and 2015 (in thousands): December 31, 2017 2016 2015 Balance at beginning of year $ — $ — $ — Expensed — — — Recoveries — — — Charge-offs and reclassifications — — — Balance at end of period $ — $ — $ — At December 31, 2017 , 2016 and 2015 , all debt and preferred equity investments were performing in accordance with the terms of the relevant investments, with the exception of a mortgage and junior mortgage participation purchased in maturity default in May 2017 and April 2017, respectively, as discussed in subnote 3 of the Debt Investments table above and a junior mortgage participation acquired in September 2014, which was acquired for zero and has a carrying value of zero , as discussed in subnote 4 of the Debt Investments table above. We have determined that we have one portfolio segment of financing receivables at December 31, 2017 and 2016 comprising commercial real estate which is primarily recorded in debt and preferred equity investments. Included in other assets is an additional amount of financing receivables totaling $65.5 million and $99.5 million at December 31, 2017 and 2016 , respectively. No financing receivables were 90 days past due at December 31, 2017 , with the exception of a mortgage and junior mortgage participation purchased in maturity default in May 2017 and April 2017, respectively, as discussed in subnote 3 of the Debt Investments table above.

Investments in Unconsolidated J

Investments in Unconsolidated Joint Ventures	12 Months Ended
	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Investments in Unconsolidated Joint Ventures	Investments in Unconsolidated Joint Ventures We have investments in several real estate joint ventures with various partners. As of December 31, 2017 , 800 Third Avenue, 21 East 66th Street, 605 West 42nd Street, 333 East 22nd Street, One Vanderbilt and certain properties within the Stonehenge Portfolio are VIEs in which we are not the primary beneficiary. Our net equity investment in these VIEs was $606.2 million as of December 31, 2017 . As of December 31, 2016 , 650 Fifth Avenue, 800 Third Avenue, 21 East 66th Street, 605 West 42nd Street, 333 East 22nd Street, and certain properties within the Stonehenge Portfolio were VIEs in which we were not the primary beneficiary. Our net equity investment in these VIEs was $220.1 million as of December 31, 2016 . Our maximum loss is limited to the amount of our equity investment in these VIEs. See the "Principles of Consolidation" section of Note 2, "Significant Accounting Policies". All other investments below are voting interest entities. As we do not control the joint ventures listed below, we account for them under the equity method of accounting. The table below provides general information on each of our joint ventures as of December 31, 2017 : Property Partner Ownership Interest (1) Economic Interest (1) Unaudited Approximate Square Feet Acquisition Date (2) Acquisition Price (2) (in thousands) 100 Park Avenue Prudential Real Estate Investors 49.90% 49.90% 834,000 February 2000 $ 95,800 717 Fifth Avenue Jeff Sutton/Private Investor 10.92% 10.92% 119,500 September 2006 251,900 800 Third Avenue Private Investors 60.52% 60.52% 526,000 December 2006 285,000 1745 Broadway Ivanhoe Cambridge, Inc. 56.87% 56.87% 674,000 April 2007 520,000 Jericho Plaza (3) Onyx Equities/Credit Suisse 11.67% 11.67% 640,000 April 2007 210,000 11 West 34th Street Private Investor/ Jeff Sutton 30.00% 30.00% 17,150 December 2010 10,800 3 Columbus Circle (4) The Moinian Group 48.90% 48.90% 741,500 January 2011 500,000 280 Park Avenue Vornado Realty Trust 50.00% 50.00% 1,219,158 March 2011 400,000 1552-1560 Broadway (5) Jeff Sutton 50.00% 50.00% 57,718 August 2011 136,550 724 Fifth Avenue Jeff Sutton 50.00% 50.00% 65,010 January 2012 223,000 10 East 53rd Street Canadian Pension Plan Investment Board 55.00% 55.00% 354,300 February 2012 252,500 521 Fifth Avenue Plaza Global Real Estate Partners LP 50.50% 50.50% 460,000 November 2012 315,000 21 East 66th Street (6) Private Investors 32.28% 32.28% 13,069 December 2012 75,000 650 Fifth Avenue (7) Jeff Sutton 50.00% 50.00% 69,214 November 2013 — 121 Greene Street Jeff Sutton 50.00% 50.00% 7,131 September 2014 27,400 175-225 Third Street Brooklyn, New York KCLW 3rd Street LLC/LIVWRK LLC 95.00% 95.00% — October 2014 74,600 55 West 46th Street Prudential Real Estate Investors 25.00% 25.00% 347,000 November 2014 295,000 Stonehenge Portfolio (8) Various Various Various 1,439,016 February 2015 36,668 131-137 Spring Street Invesco Real Estate 20.00% 20.00% 68,342 August 2015 277,750 605 West 42nd Street The Moinian Group 20.00% 20.00% 927,358 April 2016 759,000 11 Madison Avenue PGIM Real Estate 60.00% 60.00% 2,314,000 August 2016 2,605,000 333 East 22nd Street (9) Private Investors 33.33% 33.33% 26,926 August 2016 — 400 E 57th Street (10) BlackRock, Inc and Stonehenge Partners 51.00% 41.00% 290,482 October 2016 170,000 One Vanderbilt (11) National Pension Service of Korea/Hines Interest LP 71.01% 71.01% — January 2017 3,310,000 Mezzanine Loan (12) Private Investors 33.33% 33.33% — May 2017 15,000 Worldwide Plaza (13) RXR Realty / New York REIT / Private Investor 24.35% 24.35% 2,048,725 October 2017 1,725,000 1515 Broadway (14) Allianz Real Estate of America 69.87% 69.87% 1,750,000 November 2017 1,950,000 (1) Ownership interest and economic interest represent the Company's interests in the joint venture as of December 31, 2017 . Changes in ownership or economic interests within the current year are disclosed in the notes below. (2) Acquisition date and price represent the date on which the Company initially acquired an interest in the joint venture and the actual or implied gross purchase price for the joint venture on that date. Acquisition date and price are not adjusted for subsequent acquisitions or dispositions of interest. (3) During the fourth quarter of 2017, the Company recorded a $6.6 million charge in connection with this investment. This charge is included in depreciable real estate reserves in the consolidated statement of operations. (4) As a result of the sale of a condominium interest in September 2012, Young & Rubicam, Inc., or Y&R, owns floors three through eight at the property. Because the joint venture has an option to repurchase these floors, the gain associated with this sale was deferred. (5) The purchase price represents only the purchase of the 1552 Broadway interest which comprised approximately 13,045 square feet. The joint venture also owns a long-term leasehold interest in the retail space and certain other spaces at 1560 Broadway, which is adjacent to 1552 Broadway. (6) We hold a 32.28% interest in three retail and two residential units at the property and a 16.14% interest in three residential units at the property. (7) The joint venture owns a long-term leasehold interest in the retail space at 650 Fifth Avenue. In connection with the ground lease obligation, SLG provided a performance guaranty and our joint venture partner executed a contribution agreement to reflect its pro rata obligation. In the event the property is converted into a condominium unit and the landlord elects the purchase option, the joint venture shall be obligated to acquire the unit at the then fair value. (8) In March 2017, the Company sold a partial interest in the Stonehenge Portfolio as further described under Sale of Joint Venture Interest of Properties below. In February 2018, the Company, together with its joint venture partner, closed on the sale of one property from the Stonehenge Portfolio. (9) The joint venture acquired a leasehold interest in the property in October 2016. (10) In October 2016, the Company sold a 49% interest in this property to an investment account managed BlackRock, Inc. The Company's interest in the property was sold within a consolidated joint venture owned 90% by the Company and 10% by Stonehenge. The transaction resulted in the deconsolidation of the venture's remaining 51% interest in the property. The Company's joint venture with Stonehenge remains consolidated resulting in the combined 51% interest being shown within investments in unconsolidated joint ventures on the Company's balance sheet. (11) In January 2017, the Company admitted two partners, National Pension Service of Korea and Hines Interest LP, into the One Vanderbilt development project. In April 2017, the criteria for deconsolidation were met, and the development is shown within investments in unconsolidated joint ventures. The partners have committed aggregate equity to the project totaling no less than $525 million and their ownership interest in the joint venture is based on their capital contributions, up to an aggregate maximum of 29.0% . At December 31, 2017 the total of the two partners' ownership interests based on equity contributed was 3.48% . (12) In May 2017, the Company contributed a mezzanine loan secured by a commercial property in midtown Manhattan to a joint venture and retained a 33.33% interest in the venture. The carrying value is net of $10.0 million that was sold, which is included in other assets and other liabilities on the consolidated balance sheets as a result of the transfers not meeting the conditions for sale accounting. The loan matures in November 2018. (13) In September 2017, the Company and RXR Realty formed a joint venture in which each partner owns a 50% interest. In October 2017, this joint venture purchased a 48.7% interest in the property known as Worldwide Plaza from New York REIT. New York REIT owns the remaining 51.3% with its existing partner. (14) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method at December 31, 2017. Under the profit sharing method the Company recognized its share of the operations of the property and also recognized the other partner's share of depreciation. Included in equity in net income from unconsolidated joint ventures is $0.9 million of depreciation for the year ended December 31, 2017 representing the other partner's share of depreciation. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. Acquisition, Development and Construction Arrangements Based on the characteristics of the following arrangements, which are similar to those of an investment, combined with the expected residual profit of not greater than 50% , we have accounted for these debt and preferred equity investments under the equity method. As of December 31, 2017 and 2016 , the carrying value for acquisition, development and construction arrangements were as follows (in thousands): Loan Type December 31, 2017 December 31, 2016 Maturity Date Mezzanine Loan and Preferred Equity $ 100,000 $ 100,000 March 2018 Mezzanine Loan (1) 44,823 45,622 February 2022 Mezzanine Loan (2) 26,716 24,542 July 2036 $ 171,539 $ 170,164 (1) We have an option to convert our loan to an equity interest subject to certain conditions. We have determined that our option to convert the loan to equity is not a derivative financial instrument pursuant to GAAP. (2) The Company has the ability to convert this loan into an equity position starting in 2021 and the borrower is able to force this conversion in 2024. Sale of Joint Venture Interests or Properties The following table summarizes the investments in unconsolidated joint ventures sold during the years ended December 31, 2017 , 2016 , and 2015 : Property Ownership Interest Disposition Date Type of Sale Gross Asset Valuation (in thousands) (1) Gain (Loss) on Sale (in thousands) (2) 102 Greene Street 10.00% September 2017 Ownership Interest $ 43,500 $ 283 Stonehenge Portfolio (partial) Various March 2017 Ownership Interest 300,000 871 EOP Denver 0.48% September 2016 Ownership Interest 180,700 300 33 Beekman (3) 45.90% May 2016 Property 196,000 33,000 EOP Denver 4.79% March 2016 Ownership Interest 180,700 2,800 7 Renaissance Square 50.00% March 2016 Property 20,700 4,200 1 Jericho Plaza (4) 66.11% February 2016 Ownership Interest 95,200 3,300 The Meadows 50.00% August 2015 Property 121,100 (1,600 ) 315 West 36th Street 35.50% September 2015 Ownership Interest 115,000 16,300 (1) Represents implied gross valuation for the joint venture or sales price of the property. (2) Represents the Company's share of the gain or loss. The gain on sale is net of $0 , $1.1 million , and $1.2 million of employee compensation accrued in connection with the realization of these investment gains in the years ended December 31, 2017 , 2016 , and 2015 , respectively. Additionally, amounts do not include adjustments for expenses recorded in subsequent periods. (3) In connection with the sale of the property, we also recognized a promote of $10.8 million . (4) Our ownership percentage was reduced in the first quarter of 2016, from 77.78% to 11.67% , upon completion of a restructuring of the joint venture. In May 2017, our investment in a joint venture that owned two mezzanine notes secured by interests in the entity that owns 76 11th Avenue was repaid after the joint venture received repayment of the underlying loans. In May 2017, we recognized a gain of $13.0 million related to the sale in May 2014 of our ownership interest in 747 Madison Avenue. The sale did not meet the criteria for sale accounting at that time and, therefore, remained on our consolidated financial statements. The sale criteria was met in May of 2017 resulting in recognition of the deferred gain on the sale. Joint Venture Mortgages and Other Loans Payable We generally finance our joint ventures with non-recourse debt. In certain cases we have provided guarantees or master leases for tenant space, which terminate upon the satisfaction of specified circumstances or repayment of the underlying loans. The first mortgage notes and other loans payable collateralized by the respective joint venture properties and assignment of leases at December 31, 2017 and 2016 , respectively, are as follows (amounts in thousands): Property Economic Interest (1) Maturity Date Interest Rate (2) December 31, 2017 December 31, 2016 Fixed Rate Debt: 521 Fifth Avenue 50.50 % November 2019 3.73% $ 170,000 $ 170,000 717 Fifth Avenue (3) 10.92 % July 2022 4.45% 300,000 300,000 717 Fifth Avenue (3) 10.92 % July 2022 5.50% 355,328 355,328 650 Fifth Avenue (4) 50.00 % October 2022 4.46% 210,000 — 650 Fifth Avenue (4) 50.00 % October 2022 5.45% 65,000 — 21 East 66th Street 32.28 % April 2023 3.60% 12,000 12,000 3 Columbus Circle 48.90 % March 2025 3.61% 350,000 350,000 1515 Broadway 69.87 % March 2025 3.93% 872,528 — 11 Madison Avenue 60.00 % September 2025 3.84% 1,400,000 1,400,000 800 Third Avenue 60.52 % February 2026 3.37% 177,000 177,000 400 East 57th Street 41.00 % November 2026 3.00% 100,000 100,000 Worldwide Plaza 24.35 % November 2027 3.98% 1,200,000 — Stonehenge Portfolio (5) Various Various 4.17% 357,282 362,518 1745 Broadway (6) — 340,000 Total fixed rate debt $ 5,569,138 $ 3,566,846 Floating Rate Debt: Jericho Plaza (7) 11.67 % March 2018 L+ 4.15% $ 81,099 $ 76,993 724 Fifth Avenue 50.00 % April 2018 L+ 2.42% 275,000 275,000 175-225 Third Street Brooklyn, New York 95.00 % June 2018 Prime+ 1.00% 40,000 40,000 280 Park Avenue 50.00 % September 2019 L+ 1.73% 1,200,000 900,000 121 Greene Street 50.00 % November 2019 L+ 1.50% 15,000 15,000 1745 Broadway (8) 56.87 % January 2020 L+ 1.85% 345,000 — 10 East 53rd Street 55.00 % February 2020 L+ 2.25% 170,000 125,000 131-137 Spring Street 20.00 % August 2020 L+ 1.55% 141,000 141,000 1552 Broadway 50.00 % October 2020 L+ 2.65% 195,000 185,410 55 West 46th Street (9) 25.00 % November 2020 L+ 2.13% 171,444 157,322 11 West 34th Street 30.00 % January 2021 L+ 1.45% 23,000 23,000 100 Park Avenue 49.90 % February 2021 L+ 1.75% 360,000 360,000 One Vanderbilt (10) 71.01 % September 2021 L+ 3.50% 355,535 — Property Economic Interest (1) Maturity Date Interest Rate (2) December 31, 2017 December 31, 2016 605 West 42nd Street 20.00 % August 2027 L+ 1.44% 550,000 539,000 21 East 66th Street 32.28 % June 2033 1 Year Treasury+ 2.75% 1,648 1,726 Stonehenge Portfolio Various April 2018 L+ 1.25% 55,340 65,577 650 Fifth Avenue (11) — 77,500 Total floating rate debt $ 3,979,066 $ 2,982,528 Total joint venture mortgages and other loans payable $ 9,548,204 $ 6,549,374 Deferred financing costs, net (136,103 ) (95,408 ) Total joint venture mortgages and other loans payable, net $ 9,412,101 $ 6,453,966 (1) Economic interest represents the Company's interests in the joint venture as of December 31, 2017 . Changes in ownership or economic interests, if any, within the current year are disclosed in the notes to the investment in unconsolidated joint ventures note above. (2) Interest rate as of December 31, 2017 , taking into account interest rate hedges in effect during the period. Floating rate debt is presented with the stated interest rate spread over 30-day LIBOR, unless otherwise specified. (3) These loans are comprised of a $300.0 million fixed rate mortgage loan and $355.3 million mezzanine loan. The mezzanine loan is subject to accretion based on the difference between contractual interest rate and contractual pay rate. (4) In November 2017, we closed on a $65.0 million mezzanine loan with a fixed interest rate of 545 basis points and a maturity date of October 2022. As a result, the $225.0 million mortgage loan was reduced to $210.0 million with a fixed interest rate of 446 basis points. These loans are now comprised of a $210.0 million fixed rate mortgage loan and $65.0 million fixed rate mezzanine loan. (5) Amount is comprised of $33.8 million , $137.1 million , $171.6 million , and $14.8 million in fixed-rate mortgages that mature in January 2018, August 2019, June 2024, and February 2027, respectively. In January 2018, the fixed-rate mortgage set to mature in January 2018 was refinanced with a $38.0 million mortgage loan with a floating interest rate of 140 basis points over 30-day LIBOR and a maturity date of January 2021. (6) In January 2017, this loan was refinanced with a floating rate loan as shown above. (7) The property secures a two year $100.0 million loan, of which $81.1 million is currently outstanding. (8) This loan has a committed amount of $375.0 million , of which $30.0 million was unfunded as of December 31, 2017 . (9) This loan has a committed amount of $195.0 million , of which $23.6 million was unfunded as of December 31, 2017 . (10) This loan is a $1.5 billion construction facility in connection with the development of One Vanderbilt. This facility bears interest at 350 basis points over 30-day LIBOR, with reductions based on meeting certain conditions, and has an initial five -year term with two one -year extension options. Advances under the loan are subject to incurred costs, funded equity, loan to value thresholds, and entering into construction contracts. (11) In September 2017, this loan was refinanced with a fixed rate loan as shown above. We act as the operating partner and day-to-day manager for all our joint ventures, except for Worldwide Plaza, 800 Third Avenue, Jericho Plaza, 280 Park Avenue, 3 Columbus Circle, 21 East 66th Street, 175-225 Third Street, 605 West 42nd Street, 400 East 57th Street, and the Stonehenge Portfolio. We are entitled to receive fees for providing management, leasing, construction supervision and asset management services to certain of our joint ventures. We earned $22.6 million , $4.0 million and $3.4 million from these services, net of our ownership share of the joint ventures, for the years ended December 31, 2017 , 2016 , and 2015 , respectively. In addition, we have the ability to earn incentive fees based on the ultimate financial performance of certain of the joint venture properties. The combined balance sheets for the unconsolidated joint ventures, at December 31, 2017 and 2016 , are as follows (in thousands): December 31, 2017 December 31, 2016 Assets Commercial real estate property, net $ 12,822,133 $ 9,131,717 Cash and restricted cash 494,909 328,455 Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance 349,944 232,778 Debt and preferred equity investments, net 202,539 336,164 Other assets 1,407,806 683,481 Total assets $ 15,277,331 $ 10,712,595 Liabilities and members' equity Mortgages and other loans payable, net $ 9,412,101 $ 6,453,966 Deferred revenue/gain 985,648 356,414 Other liabilities 411,053 391,500 Members' equity 4,468,529 3,510,715 Total liabilities and members' equity $ 15,277,331 $ 10,712,595 Company's investments in unconsolidated joint ventures $ 2,362,989 $ 1,890,186 The combined statements of operations for the unconsolidated joint ventures, from acquisition date through the years ended December 31, 2017 , 2016 , and 2015 are as follows (in thousands): Year Ended December 31, 2017 2016 2015 Total revenues $ 904,230 $ 712,689 $ 576,845 Operating expenses 157,610 126,913 106,613 Ground rent 16,794 14,924 14,083 Real estate taxes 142,774 111,673 89,734 Interest expense, net of interest income 250,063 197,741 199,126 Amortization of deferred financing costs 23,026 24,829 13,394 Transaction related costs 146 5,566 615 Depreciation and amortization 279,419 199,011 149,023 Total expenses $ 869,832 $ 680,657 $ 572,588 Loss on early extinguishment of debt (7,899 ) (1,606 ) (1,089 ) Net income before gain on sale $ 26,499 $ 30,426 $ 3,168 Company's equity in net income from unconsolidated joint ventures $ 21,892 $ 11,874 $ 13,028

Deferred Costs

Deferred Costs	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred Costs	Deferred Costs Deferred costs at December 31, 2017 and 2016 consisted of the following (in thousands): December 31, 2017 2016 Deferred leasing costs $ 443,341 $ 468,971 Less: accumulated amortization (217,140 ) (201,371 ) Deferred costs, net $ 226,201 $ 267,600

Mortgages and Other Loans Payab

Mortgages and Other Loans Payable	12 Months Ended
	Dec. 31, 2017
Mortgages and Other Loans Payable
Mortgages and Other Loans Payable	Mortgages and Other Loans Payable The first mortgages and other loans payable collateralized by the respective properties and assignment of leases or debt investments at December 31, 2017 and 2016 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) December 31, 2017 December 31, 2016 Fixed Rate Debt: Unsecured Loan June 2018 4.81% $ 16,000 $ 16,000 One Madison Avenue May 2020 5.91% 486,153 517,806 762 Madison Avenue February 2022 5.00% 771 7,694 100 Church Street July 2022 4.68% 217,273 221,446 919 Third Avenue (2) June 2023 5.12% 500,000 500,000 420 Lexington Avenue October 2024 3.99% 300,000 300,000 400 East 58th Street (3) November 2026 3.00% 40,000 40,000 Landmark Square January 2027 4.90% 100,000 100,000 485 Lexington Avenue February 2027 4.25% 450,000 450,000 1080 Amsterdam (4) February 2027 3.58% 36,363 — 315 West 33rd Street February 2027 4.17% 250,000 — Series J Preferred Units (5) April 2051 3.75% 4,000 4,000 1515 Broadway (6) — 888,531 885 Third Avenue (7) — 267,650 FHLBNY Facility (8) — 105,000 FHLBNY Facility (8) — 100,000 Total fixed rate debt $ 2,400,560 $ 3,518,127 Floating Rate Debt: 719 Seventh Avenue (9) February 2018 L+ 3.05% $ 41,622 $ 37,388 183, 187 Broadway & 5-7 Dey Street May 2018 L+ 2.70% 58,000 58,000 2017 Master Repurchase Agreement June 2018 L+ 2.38% 90,809 — 220 East 42nd Street October 2020 L+ 1.60% 275,000 275,000 2016 Master Repurchase Agreement (10) — 184,642 One Vanderbilt Avenue (11) — 64,030 1080 Amsterdam (12) — 3,525 Total floating rate debt $ 465,431 $ 622,585 Total fixed rate and floating rate debt $ 2,865,991 $ 4,140,712 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 2,865,991 $ 4,140,712 Deferred financing costs, net of amortization (28,709 ) (66,882 ) Total mortgages and other loans payable, net $ 2,837,282 $ 4,073,830 (1) Interest rate as of December 31, 2017 , taking into account interest rate hedges in effect during the period. Floating rate debt is presented with the stated interest rate spread over 30-day LIBOR, unless otherwise specified. (2) We own a 51.0% controlling interest in the consolidated joint venture that is the borrower on this loan. In January 2018, the partnership agreement for our investment in the property at 919 Third Avenue was modified resulting in our partner now having substantive participating rights in the venture. As a result the investment will no longer be deemed a VIE and our investment in the property will be deconsolidated as of January 1, 2018. (3) The loan carries a fixed interest rate of 300 basis points for the first five years and is prepayable without penalty at the end of year five . (4) The loan is comprised of a $35.5 million mortgage loan and $0.9 million subordinate loan with a fixed interest rate of 350 basis points and 700 basis points, respectively, for the first five years and is prepayable without penalty at the end of year five . (5) In connection with the acquisition of a commercial real estate property, the Operating Partnership issued $4.0 million , 3.75% Series J Preferred Units of limited partnership interest, or the Series J Preferred Units, with a mandatory liquidation preference of $1,000 per unit. The Series J Preferred Units are accounted for as debt because they can be redeemed in cash by the Operating Partnership on the earlier of (i) the date of the sale of the property or (ii) April 30, 2051 or at the option of the unitholders as provided for in the related agreement. (6) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. This property is presented as an unconsolidated joint venture as of December 31, 2017 . The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. (7) In February 2016, we closed on the sale of 885 Third Avenue. The sale did not meet the criteria for sale accounting at that time. In April 2017, the mortgage was refinanced by the buyer, resulting in the Company deconsolidating the property from its financial statements in the second quarter of 2017. (8) The facility was repaid in January 2017. (9) In January 2018, we exercised an one year extension option to extend the maturity date to February 2019. (10) The master repurchase agreement was repaid in October 2017. (11) In September 2016, we closed on a $1.5 billion construction facility in connection with the development of One Vanderbilt Avenue. In January 2017, we admitted two partners, National Pension Service of Korea and Hines Interest LP, into the One Vanderbilt Avenue development project. In April 2017, the criteria for deconsolidation were met, and the development is shown within investments in unconsolidated joint ventures. See Note 6, "Investments in Unconsolidated Joint Ventures". (12) In January 2017, this loan was refinanced with a fixed rate loan as shown above. At December 31, 2017 and 2016 , the gross book value of the properties and debt and preferred equity investments collateralizing the mortgages and other loans payable, not including assets held for sale, was approximately $4.8 billion and $6.0 billion , respectively. Federal Home Loan Bank of New York Facility The Company’s wholly-owned subsidiary, Belmont Insurance Company, or Belmont, a New York licensed captive insurance company, was a member of the Federal Home Loan Bank of New York, or FHLBNY. In January 2017, all funds borrowed from the FHLBNY were repaid and Belmont's membership was terminated in February 2017. Master Repurchase Agreements The Company has entered into two Master Repurchase Agreements, or MRAs, known as the 2016 MRA and 2017 MRA, which provide us with the ability to sell certain debt investments with a simultaneous agreement to repurchase the same at a certain date or on demand. We seek to mitigate risks associated with our repurchase agreement by managing the credit quality of our assets, early repayments, interest rate volatility, liquidity, and market value. The margin call provisions under our repurchase facilities permit valuation adjustments based on capital markets activity, and are not limited to collateral-specific credit marks. To monitor credit risk associated with our debt investments, our asset management team regularly reviews our investment portfolio and is in contact with our borrowers in order to monitor the collateral and enforce our rights as necessary. The risk associated with potential margin calls is further mitigated by our ability to recollateralize the facility with additional assets from our portfolio of debt investments, our ability to satisfy margin calls with cash or cash equivalents and our access to additional liquidity through the 2017 credit facility, as defined below. In June 2017, we entered into the 2017 MRA, with a maximum facility capacity of $300.0 million . The facility bears interest on a floating rate basis at a spread to 30-day LIBOR based on the pledged collateral and advance rate and has an initial one year term, with two one year extension options. At December 31, 2017 , the facility had a carrying value of $90.1 million , net of deferred financing costs. In July 2016, we entered into a restated 2016 MRA, with a maximum facility capacity of $300.0 million . The facility bears interest ranging from 225 and 400 basis points over 30-day LIBOR depending on the pledged collateral and has an initial two -year term, with a one year extension option. Since December 6, 2015, we have been required to pay monthly in arrears a 25 basis point fee on the excess of $150.0 million over the average daily balance during the period when the average daily balance is less than $150.0 million . At December 31, 2017 , the facility had a carrying value of $(1.2) million , representing deferred financing costs presented within other liabilities. Corporate Indebtedness 2017 Credit Facility In November 2017, we entered into an amendment to the credit facility, referred to as the 2017 credit facility, that was originally entered into by the Company in November 2012, or the 2012 credit facility. As of December 31, 2017 , the 2017 credit facility consisted of a $1.5 billion revolving credit facility, a $1.3 billion term loan (or "Term Loan A"), and a $200.0 million term loan (or "Term Loan B") with maturity dates of March 31, 2022, March 31, 2023, and November 21, 2024, respectively. The revolving credit facility has two six -month as-of-right extension options to March 31, 2023. We also have an option, subject to customary conditions, to increase the capacity of the credit facility to $4.5 billion at any time prior to the maturity dates for the revolving credit facility and term loans without the consent of existing lenders, by obtaining additional commitments from our existing lenders and other financial institutions. As of December 31, 2017 , the 2017 credit facility bore interest at a spread over 30-day LIBOR ranging from (i) 82.5 basis points to 155 basis points for loans under the revolving credit facility, (ii) 90 basis points to 175 basis points for loans under Term Loan A, and (iii) 150 basis points to 245 basis points for loans under Term Loan B, in each case based on the credit rating assigned to the senior unsecured long term indebtedness of the Company. At December 31, 2017 , the applicable spread was 100 basis points for the revolving credit facility, 110 basis points for Term Loan A, and 165 basis points for Term Loan B. We are required to pay quarterly in arrears a 12.5 to 30 basis point facility fee on the total commitments under the revolving credit facility based on the credit rating assigned to the senior unsecured long term indebtedness of the Company. As of December 31, 2017 , the facility fee was 20 basis points. As of December 31, 2017 , we had $11.8 million of outstanding letters of credit, $40.0 million drawn under the revolving credit facility and $1.5 billion outstanding under the term loan facilities, with total undrawn capacity of $1.4 billion under the 2017 credit facility. At December 31, 2017 and December 31, 2016 , the revolving credit facility had a carrying value of $30.3 million and $(6.3) million , respectively, net of deferred financing costs. The December 31, 2016 carrying value represents deferred financing costs and is presented within other liabilities. At December 31, 2017 and December 31, 2016 , the term loan facilities had a carrying value of $1.5 billion and $1.2 billion , respectively, net of deferred financing costs. The Company and the Operating Partnership are borrowers jointly and severally obligated under the 2017 credit facility. ROP is a guarantor under the 2017 credit facility. The 2017 credit facility includes certain restrictions and covenants (see Restrictive Covenants below). Senior Unsecured Notes The following table sets forth our senior unsecured notes and other related disclosures as of December 31, 2017 and 2016 , respectively, by scheduled maturity date (dollars in thousands): Issuance December 31, 2017 Unpaid Principal Balance December 31, 2017 Accreted Balance December 31, 2016 Accreted Balance Coupon Rate (1) Initial Term (in Years) Maturity Date August 5, 2011 (2) $ 250,000 $ 249,953 $ 249,880 5.00 % 7 August 2018 March 16, 2010 (2) 250,000 250,000 250,000 7.75 % 10 March 2020 October 5, 2017 (3) 500,000 499,489 — 3.25 % 5 October 2022 November 15, 2012 (4) 300,000 305,163 200,000 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 October 12, 2010 (5) — — 334,077 $ 1,400,000 $ 1,404,605 $ 1,133,957 Deferred financing costs, net (8,666 ) (5,642 ) $ 1,400,000 $ 1,395,939 $ 1,128,315 (1) Interest on the senior unsecured notes is payable semi-annually with principal and unpaid interest due on the scheduled maturity dates. (2) Issued by the Company, the Operating Partnership and ROP, as co-obligors. (3) Issued by the Operating Partnership with the Company and ROP as guarantors. (4) In October 2017, the Company, the Operating Partnership and ROP, as co-obligors, issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022. The notes were priced at 105.334% . (5) In accordance with the terms of the indenture, the notes became exchangeable commencing September 14, 2017 and the Operating Partnership elected to settle exchanges in cash. In October 2017, all note holders elected to exchange the notes and the notes were repaid for $350.8 million , excluding accrued interest based on the applicable exchange rate. Restrictive Covenants The terms of the 2017 credit facility and certain of our senior unsecured notes include certain restrictions and covenants which may limit, among other things, our ability to pay dividends, make certain types of investments, incur additional indebtedness, incur liens and enter into negative pledge agreements and dispose of assets, and which require compliance with financial ratios relating to the maximum ratio of total indebtedness to total asset value, a minimum ratio of EBITDA to fixed charges, a maximum ratio of secured indebtedness to total asset value and a maximum ratio of unsecured indebtedness to unencumbered asset value. The dividend restriction referred to above provides that, we will not during any time when a default is continuing, make distributions with respect to common stock or other equity interests, except to enable the Company to continue to qualify as a REIT for Federal income tax purposes. As of December 31, 2017 and 2016 , we were in compliance with all such covenants. Junior Subordinated Deferrable Interest Debentures In June 2005, the Company and the Operating Partnership issued $100.0 million in unsecured trust preferred securities through a newly formed trust, SL Green Capital Trust I, or the Trust, which is a wholly-owned subsidiary of the Operating Partnership. The securities mature in 2035 and bear interest at a floating rate of 125 basis points over the three-month LIBOR. Interest payments may be deferred for a period of up to eight consecutive quarters if the Operating Partnership exercises its right to defer such payments. The Trust preferred securities are redeemable at the option of the Operating Partnership, in whole or in part, with no prepayment premium. We do not consolidate the Trust even though it is a variable interest entity as we are not the primary beneficiary. Because the Trust is not consolidated, we have recorded the debt on our consolidated balance sheets and the related payments are classified as interest expense. Principal Maturities Combined aggregate principal maturities of mortgages and other loans payable, 2017 credit facility, trust preferred securities, senior unsecured notes and our share of joint venture debt as of December 31, 2017 , including as-of-right extension options and put options, were as follows (in thousands): Scheduled Amortization Principal Revolving Credit Facility Unsecured Term Loans Trust Preferred Securities Senior Unsecured Notes Total Joint Venture Debt 2018 $ 37,971 $ 206,431 $ — $ — $ — $ 250,000 $ 494,402 $ 200,250 2019 42,289 — — — — — 42,289 717,682 2020 23,487 679,531 — — — 250,000 953,018 473,809 2021 11,656 — — — — — 11,656 449,740 2022 9,448 198,555 — — — 800,000 1,008,003 223,330 Thereafter 16,675 1,639,948 40,000 1,500,000 100,000 100,000 3,396,623 2,119,481 $ 141,526 $ 2,724,465 $ 40,000 $ 1,500,000 $ 100,000 $ 1,400,000 $ 5,905,991 $ 4,184,292 Consolidated interest expense, excluding capitalized interest, was comprised of the following (in thousands): Year Ended December 31, 2017 2016 2015 Interest expense before capitalized interest $ 284,649 $ 348,062 $ 357,926 Interest capitalized (26,020 ) (24,067 ) (31,108 ) Interest income (1,584 ) (2,796 ) (2,948 ) Interest expense, net $ 257,045 $ 321,199 $ 323,870

Corporate Indebtedness

Corporate Indebtedness	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Corporate Indebtedness	Mortgages and Other Loans Payable The first mortgages and other loans payable collateralized by the respective properties and assignment of leases or debt investments at December 31, 2017 and 2016 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) December 31, 2017 December 31, 2016 Fixed Rate Debt: Unsecured Loan June 2018 4.81% $ 16,000 $ 16,000 One Madison Avenue May 2020 5.91% 486,153 517,806 762 Madison Avenue February 2022 5.00% 771 7,694 100 Church Street July 2022 4.68% 217,273 221,446 919 Third Avenue (2) June 2023 5.12% 500,000 500,000 420 Lexington Avenue October 2024 3.99% 300,000 300,000 400 East 58th Street (3) November 2026 3.00% 40,000 40,000 Landmark Square January 2027 4.90% 100,000 100,000 485 Lexington Avenue February 2027 4.25% 450,000 450,000 1080 Amsterdam (4) February 2027 3.58% 36,363 — 315 West 33rd Street February 2027 4.17% 250,000 — Series J Preferred Units (5) April 2051 3.75% 4,000 4,000 1515 Broadway (6) — 888,531 885 Third Avenue (7) — 267,650 FHLBNY Facility (8) — 105,000 FHLBNY Facility (8) — 100,000 Total fixed rate debt $ 2,400,560 $ 3,518,127 Floating Rate Debt: 719 Seventh Avenue (9) February 2018 L+ 3.05% $ 41,622 $ 37,388 183, 187 Broadway & 5-7 Dey Street May 2018 L+ 2.70% 58,000 58,000 2017 Master Repurchase Agreement June 2018 L+ 2.38% 90,809 — 220 East 42nd Street October 2020 L+ 1.60% 275,000 275,000 2016 Master Repurchase Agreement (10) — 184,642 One Vanderbilt Avenue (11) — 64,030 1080 Amsterdam (12) — 3,525 Total floating rate debt $ 465,431 $ 622,585 Total fixed rate and floating rate debt $ 2,865,991 $ 4,140,712 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 2,865,991 $ 4,140,712 Deferred financing costs, net of amortization (28,709 ) (66,882 ) Total mortgages and other loans payable, net $ 2,837,282 $ 4,073,830 (1) Interest rate as of December 31, 2017 , taking into account interest rate hedges in effect during the period. Floating rate debt is presented with the stated interest rate spread over 30-day LIBOR, unless otherwise specified. (2) We own a 51.0% controlling interest in the consolidated joint venture that is the borrower on this loan. In January 2018, the partnership agreement for our investment in the property at 919 Third Avenue was modified resulting in our partner now having substantive participating rights in the venture. As a result the investment will no longer be deemed a VIE and our investment in the property will be deconsolidated as of January 1, 2018. (3) The loan carries a fixed interest rate of 300 basis points for the first five years and is prepayable without penalty at the end of year five . (4) The loan is comprised of a $35.5 million mortgage loan and $0.9 million subordinate loan with a fixed interest rate of 350 basis points and 700 basis points, respectively, for the first five years and is prepayable without penalty at the end of year five . (5) In connection with the acquisition of a commercial real estate property, the Operating Partnership issued $4.0 million , 3.75% Series J Preferred Units of limited partnership interest, or the Series J Preferred Units, with a mandatory liquidation preference of $1,000 per unit. The Series J Preferred Units are accounted for as debt because they can be redeemed in cash by the Operating Partnership on the earlier of (i) the date of the sale of the property or (ii) April 30, 2051 or at the option of the unitholders as provided for in the related agreement. (6) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. This property is presented as an unconsolidated joint venture as of December 31, 2017 . The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. (7) In February 2016, we closed on the sale of 885 Third Avenue. The sale did not meet the criteria for sale accounting at that time. In April 2017, the mortgage was refinanced by the buyer, resulting in the Company deconsolidating the property from its financial statements in the second quarter of 2017. (8) The facility was repaid in January 2017. (9) In January 2018, we exercised an one year extension option to extend the maturity date to February 2019. (10) The master repurchase agreement was repaid in October 2017. (11) In September 2016, we closed on a $1.5 billion construction facility in connection with the development of One Vanderbilt Avenue. In January 2017, we admitted two partners, National Pension Service of Korea and Hines Interest LP, into the One Vanderbilt Avenue development project. In April 2017, the criteria for deconsolidation were met, and the development is shown within investments in unconsolidated joint ventures. See Note 6, "Investments in Unconsolidated Joint Ventures". (12) In January 2017, this loan was refinanced with a fixed rate loan as shown above. At December 31, 2017 and 2016 , the gross book value of the properties and debt and preferred equity investments collateralizing the mortgages and other loans payable, not including assets held for sale, was approximately $4.8 billion and $6.0 billion , respectively. Federal Home Loan Bank of New York Facility The Company’s wholly-owned subsidiary, Belmont Insurance Company, or Belmont, a New York licensed captive insurance company, was a member of the Federal Home Loan Bank of New York, or FHLBNY. In January 2017, all funds borrowed from the FHLBNY were repaid and Belmont's membership was terminated in February 2017. Master Repurchase Agreements The Company has entered into two Master Repurchase Agreements, or MRAs, known as the 2016 MRA and 2017 MRA, which provide us with the ability to sell certain debt investments with a simultaneous agreement to repurchase the same at a certain date or on demand. We seek to mitigate risks associated with our repurchase agreement by managing the credit quality of our assets, early repayments, interest rate volatility, liquidity, and market value. The margin call provisions under our repurchase facilities permit valuation adjustments based on capital markets activity, and are not limited to collateral-specific credit marks. To monitor credit risk associated with our debt investments, our asset management team regularly reviews our investment portfolio and is in contact with our borrowers in order to monitor the collateral and enforce our rights as necessary. The risk associated with potential margin calls is further mitigated by our ability to recollateralize the facility with additional assets from our portfolio of debt investments, our ability to satisfy margin calls with cash or cash equivalents and our access to additional liquidity through the 2017 credit facility, as defined below. In June 2017, we entered into the 2017 MRA, with a maximum facility capacity of $300.0 million . The facility bears interest on a floating rate basis at a spread to 30-day LIBOR based on the pledged collateral and advance rate and has an initial one year term, with two one year extension options. At December 31, 2017 , the facility had a carrying value of $90.1 million , net of deferred financing costs. In July 2016, we entered into a restated 2016 MRA, with a maximum facility capacity of $300.0 million . The facility bears interest ranging from 225 and 400 basis points over 30-day LIBOR depending on the pledged collateral and has an initial two -year term, with a one year extension option. Since December 6, 2015, we have been required to pay monthly in arrears a 25 basis point fee on the excess of $150.0 million over the average daily balance during the period when the average daily balance is less than $150.0 million . At December 31, 2017 , the facility had a carrying value of $(1.2) million , representing deferred financing costs presented within other liabilities. Corporate Indebtedness 2017 Credit Facility In November 2017, we entered into an amendment to the credit facility, referred to as the 2017 credit facility, that was originally entered into by the Company in November 2012, or the 2012 credit facility. As of December 31, 2017 , the 2017 credit facility consisted of a $1.5 billion revolving credit facility, a $1.3 billion term loan (or "Term Loan A"), and a $200.0 million term loan (or "Term Loan B") with maturity dates of March 31, 2022, March 31, 2023, and November 21, 2024, respectively. The revolving credit facility has two six -month as-of-right extension options to March 31, 2023. We also have an option, subject to customary conditions, to increase the capacity of the credit facility to $4.5 billion at any time prior to the maturity dates for the revolving credit facility and term loans without the consent of existing lenders, by obtaining additional commitments from our existing lenders and other financial institutions. As of December 31, 2017 , the 2017 credit facility bore interest at a spread over 30-day LIBOR ranging from (i) 82.5 basis points to 155 basis points for loans under the revolving credit facility, (ii) 90 basis points to 175 basis points for loans under Term Loan A, and (iii) 150 basis points to 245 basis points for loans under Term Loan B, in each case based on the credit rating assigned to the senior unsecured long term indebtedness of the Company. At December 31, 2017 , the applicable spread was 100 basis points for the revolving credit facility, 110 basis points for Term Loan A, and 165 basis points for Term Loan B. We are required to pay quarterly in arrears a 12.5 to 30 basis point facility fee on the total commitments under the revolving credit facility based on the credit rating assigned to the senior unsecured long term indebtedness of the Company. As of December 31, 2017 , the facility fee was 20 basis points. As of December 31, 2017 , we had $11.8 million of outstanding letters of credit, $40.0 million drawn under the revolving credit facility and $1.5 billion outstanding under the term loan facilities, with total undrawn capacity of $1.4 billion under the 2017 credit facility. At December 31, 2017 and December 31, 2016 , the revolving credit facility had a carrying value of $30.3 million and $(6.3) million , respectively, net of deferred financing costs. The December 31, 2016 carrying value represents deferred financing costs and is presented within other liabilities. At December 31, 2017 and December 31, 2016 , the term loan facilities had a carrying value of $1.5 billion and $1.2 billion , respectively, net of deferred financing costs. The Company and the Operating Partnership are borrowers jointly and severally obligated under the 2017 credit facility. ROP is a guarantor under the 2017 credit facility. The 2017 credit facility includes certain restrictions and covenants (see Restrictive Covenants below). Senior Unsecured Notes The following table sets forth our senior unsecured notes and other related disclosures as of December 31, 2017 and 2016 , respectively, by scheduled maturity date (dollars in thousands): Issuance December 31, 2017 Unpaid Principal Balance December 31, 2017 Accreted Balance December 31, 2016 Accreted Balance Coupon Rate (1) Initial Term (in Years) Maturity Date August 5, 2011 (2) $ 250,000 $ 249,953 $ 249,880 5.00 % 7 August 2018 March 16, 2010 (2) 250,000 250,000 250,000 7.75 % 10 March 2020 October 5, 2017 (3) 500,000 499,489 — 3.25 % 5 October 2022 November 15, 2012 (4) 300,000 305,163 200,000 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 October 12, 2010 (5) — — 334,077 $ 1,400,000 $ 1,404,605 $ 1,133,957 Deferred financing costs, net (8,666 ) (5,642 ) $ 1,400,000 $ 1,395,939 $ 1,128,315 (1) Interest on the senior unsecured notes is payable semi-annually with principal and unpaid interest due on the scheduled maturity dates. (2) Issued by the Company, the Operating Partnership and ROP, as co-obligors. (3) Issued by the Operating Partnership with the Company and ROP as guarantors. (4) In October 2017, the Company, the Operating Partnership and ROP, as co-obligors, issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022. The notes were priced at 105.334% . (5) In accordance with the terms of the indenture, the notes became exchangeable commencing September 14, 2017 and the Operating Partnership elected to settle exchanges in cash. In October 2017, all note holders elected to exchange the notes and the notes were repaid for $350.8 million , excluding accrued interest based on the applicable exchange rate. Restrictive Covenants The terms of the 2017 credit facility and certain of our senior unsecured notes include certain restrictions and covenants which may limit, among other things, our ability to pay dividends, make certain types of investments, incur additional indebtedness, incur liens and enter into negative pledge agreements and dispose of assets, and which require compliance with financial ratios relating to the maximum ratio of total indebtedness to total asset value, a minimum ratio of EBITDA to fixed charges, a maximum ratio of secured indebtedness to total asset value and a maximum ratio of unsecured indebtedness to unencumbered asset value. The dividend restriction referred to above provides that, we will not during any time when a default is continuing, make distributions with respect to common stock or other equity interests, except to enable the Company to continue to qualify as a REIT for Federal income tax purposes. As of December 31, 2017 and 2016 , we were in compliance with all such covenants. Junior Subordinated Deferrable Interest Debentures In June 2005, the Company and the Operating Partnership issued $100.0 million in unsecured trust preferred securities through a newly formed trust, SL Green Capital Trust I, or the Trust, which is a wholly-owned subsidiary of the Operating Partnership. The securities mature in 2035 and bear interest at a floating rate of 125 basis points over the three-month LIBOR. Interest payments may be deferred for a period of up to eight consecutive quarters if the Operating Partnership exercises its right to defer such payments. The Trust preferred securities are redeemable at the option of the Operating Partnership, in whole or in part, with no prepayment premium. We do not consolidate the Trust even though it is a variable interest entity as we are not the primary beneficiary. Because the Trust is not consolidated, we have recorded the debt on our consolidated balance sheets and the related payments are classified as interest expense. Principal Maturities Combined aggregate principal maturities of mortgages and other loans payable, 2017 credit facility, trust preferred securities, senior unsecured notes and our share of joint venture debt as of December 31, 2017 , including as-of-right extension options and put options, were as follows (in thousands): Scheduled Amortization Principal Revolving Credit Facility Unsecured Term Loans Trust Preferred Securities Senior Unsecured Notes Total Joint Venture Debt 2018 $ 37,971 $ 206,431 $ — $ — $ — $ 250,000 $ 494,402 $ 200,250 2019 42,289 — — — — — 42,289 717,682 2020 23,487 679,531 — — — 250,000 953,018 473,809 2021 11,656 — — — — — 11,656 449,740 2022 9,448 198,555 — — — 800,000 1,008,003 223,330 Thereafter 16,675 1,639,948 40,000 1,500,000 100,000 100,000 3,396,623 2,119,481 $ 141,526 $ 2,724,465 $ 40,000 $ 1,500,000 $ 100,000 $ 1,400,000 $ 5,905,991 $ 4,184,292 Consolidated interest expense, excluding capitalized interest, was comprised of the following (in thousands): Year Ended December 31, 2017 2016 2015 Interest expense before capitalized interest $ 284,649 $ 348,062 $ 357,926 Interest capitalized (26,020 ) (24,067 ) (31,108 ) Interest income (1,584 ) (2,796 ) (2,948 ) Interest expense, net $ 257,045 $ 321,199 $ 323,870

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Cleaning/ Security/ Messenger and Restoration Services Alliance Building Services, or Alliance, and its affiliates are partially owned by Gary Green, a son of Stephen L. Green, the chairman of our board of directors, and provide services to certain properties owned by us. Alliance’s affiliates include First Quality Maintenance, L.P., or First Quality, Classic Security LLC, Bright Star Couriers LLC and Onyx Restoration Works, and provide cleaning, extermination, security, messenger, and restoration services, respectively. In addition, First Quality has the non-exclusive opportunity to provide cleaning and related services to individual tenants at our properties on a basis separately negotiated with any tenant seeking such additional services. The Service Corporation has entered into an arrangement with Alliance whereby it will receive a profit participation above a certain threshold for services provided by Alliance to certain tenants at certain buildings above the base services specified in their lease agreements. Income earned from the profit participation, which is included in other income on the consolidated statements of operations, was $3.9 million , $3.5 million and $3.8 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. We also recorded expenses, inclusive of capitalized expenses, of $22.6 million , $23.4 million and $21.3 million the years ended December 31, 2017 , 2016 and 2015 , respectively, for these services (excluding services provided directly to tenants). Management Fees S.L. Green Management Corp., a consolidated entity, receives property management fees from an entity in which Stephen L. Green owns an interest. We received management fees from this entity of $0.5 million , $0.7 million and $0.5 million for the years ended December 31, 2017 , 2016 , and 2015 respectively. One Vanderbilt Investment In December 2016, we entered into agreements with entities owned and controlled by Marc Holliday and Andrew Mathias, pursuant to which they agreed to make an investment in our One Vanderbilt project at the appraised fair market value for the interests acquired. This investment entitles these entities to receive approximately 1.50 % - 1.80 % and 1.00 % - 1.20 %, respectively, of any profits realized by the Company from its One Vanderbilt project in excess of the Company’s capital contributions. The entities have no right to any return of capital. Accordingly, subject to previously disclosed repurchase rights, these interests will have no value and will not entitle these entities to any amounts (other than limited distributions to cover tax liabilities incurred) unless and until the Company has received distributions from the One Vanderbilt project in excess of the Company’s aggregate investment in the project. In the event that the Company does not realize a profit on its investment in the project (or would not realize a profit based on the value at the time the interests are repurchased), the entities owned and controlled by Messrs. Holliday and Mathias will lose the entire amount of their investment. The entities owned and controlled by Messrs. Holliday and Mathias paid $1.4 million and $1.0 million , respectively, which equal the fair market value of the interests acquired as of the date the investment agreements were entered into as determined by an independent third party appraisal that we obtained. Messrs. Holliday and Mathias cannot monetize their interests until after stabilization of the property ( 50% within three years after stabilization and 100% three years or more after stabilization). In addition, the agreement calls for us to repurchase these interests in the event of a sale of One Vanderbilt or a transactional change of control of the Company. We also have the right to repurchase these interests on the seven -year anniversary of the stabilization of the project or upon the occurrence of certain separation events prior to the stabilization of the project relating to each of Messrs. Holliday’s and Mathias’s continued service with us. The price paid upon monetization of the interests will equal the liquidation value of the interests at the time, with the value of One Vanderbilt being based on its sale price, if applicable, or fair market value as determined by an independent third party appraiser. Other We are entitled to receive fees for providing management, leasing, construction supervision, and asset management services to certain of our joint ventures as further described in Note 6, "Investments in Unconsolidated Joint Ventures". Amounts due from joint ventures and related parties at December 31, 2017 and 2016 consisted of the following (in thousands): December 31, 2017 2016 Due from joint ventures $ 15,025 $ 1,240 Other 8,014 14,616 Related party receivables $ 23,039 $ 15,856

Noncontrolling Interests on the

Noncontrolling Interests on the Company's Consolidated Financial Statements	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Noncontrolling Interests on the Company's Consolidated Financial Statements	Noncontrolling Interests on the Company's Consolidated Financial Statements Noncontrolling interests represent the common and preferred units of limited partnership interest in the Operating Partnership not held by the Company as well as third party equity interests in our other consolidated subsidiaries. Noncontrolling interests in the Operating Partnership are shown in the mezzanine equity while the noncontrolling interests in our other consolidated subsidiaries are shown in the equity section of the Company’s consolidated financial statements. Common Units of Limited Partnership Interest in the Operating Partnership As of December 31, 2017 and 2016 , the noncontrolling interest unit holders owned 4.58% , or 4,452,979 units, and 4.16% , or 4,363,716 units, of the Operating Partnership, respectively. At December 31, 2017 , 4,452,979 shares of our common stock were reserved for issuance upon the redemption of units of limited partnership interest of the Operating Partnership. Noncontrolling interests in the Operating Partnership is recorded at the greater of its cost basis or fair market value based on the closing stock price of our common stock at the end of the reporting period. Below is the rollforward analysis of the activity relating to the noncontrolling interests in the Operating Partnership as of December 31, 2017 and 2016 (in thousands): December 31, 2017 2016 Balance at beginning of period $ 473,882 $ 424,206 Distributions (14,266 ) (12,671 ) Issuance of common units 25,723 78,495 Redemption of common units (21,574 ) (31,805 ) Net income 3,995 10,136 Accumulated other comprehensive income allocation (94 ) 1,299 Fair value adjustment (5,712 ) 4,222 Balance at end of period $ 461,954 $ 473,882 Preferred Units of Limited Partnership Interest in the Operating Partnership The Operating Partnership has 1,902,000 4.50% Series G Preferred Units of limited partnership interest, or the Series G Preferred Units outstanding, with a liquidation preference of $25.00 per unit, which were issued in January 2012 in conjunction with an acquisition. The Series G Preferred unitholders receive annual dividends of $1.125 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Series G Preferred Units are convertible into a number of common units of limited partnership interest in the Operating Partnership equal to (i) the liquidation preference plus accumulated and unpaid distributions on the conversion date divided by (ii) $88.50 . The common units of limited partnership interest in the Operating Partnership may be redeemed in exchange for our common stock on a 1 -to-1 basis. The Series G Preferred Units also provide the holder with the right to require the Operating Partnership to repurchase the Series G Preferred Units for cash before January 31, 2022. The Operating Partnership has 60 Series F Preferred Units outstanding with a mandatory liquidation preference of $1,000.00 per unit. The Operating Partnership has authorized up to 700,000 3.50% Series K Preferred Units of limited partnership interest, or the Series K Preferred Units, with a liquidation preference of $25.00 per unit. In August 2014, the Company issued 563,954 Series K Preferred Units in conjunction with an acquisition. The Series K Preferred unitholders receive annual dividends of $0.875 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Series K Preferred Units can be redeemed at any time, at the option of the unitholder, either for cash or are convertible into a number of common units of limited partnership interest in the Operating Partnership equal to (i) the liquidation preference plus accumulated and unpaid distributions on the conversion date divided by (ii) $134.67 . The Operating Partnership has authorized up to 500,000 4.00% Series L Preferred Units of limited partnership interest, or the Series L Preferred Units, with a liquidation preference of $25.00 per unit. In August 2014, the Company issued 378,634 Series L Preferred Units in conjunction with an acquisition. The Series L Preferred unitholders receive annual dividends of $1.00 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Series L Preferred Units can be redeemed at any time at par for cash at the option of the unitholder. The Operating Partnership has authorized up to 1,600,000 3.75% Series M Preferred Units of limited partnership interest, or the Series M Preferred Units, with a liquidation preference of $25.00 per unit. In February 2015, the Company issued 1,600,000 Series M Preferred Units in conjunction with the acquisition of ownership interests in and relating to certain residential and retail real estate properties. The Series M Preferred unitholders receive annual dividends of $0.9375 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Series M Preferred Units can be redeemed at any time at par for cash at the option of the unitholder. The Operating Partnership has authorized up to 552,303 3.00% Series N Preferred Units of limited partnership interest, or the Series N Preferred Units, with a liquidation preference of $25.00 per unit. In June 2015, the Company issued 552,303 Series N Preferred Units in conjunction with an acquisition. The Series N Preferred unitholders receive annual dividends of $0.75 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Series N Preferred Units can be redeemed at any time at par for cash at the option of the unitholder. The Operating Partnership has authorized an aggregate of one 6.25% Series O Preferred Unit of limited partnership interest, or the Series O Preferred Unit. In June 2015, the Company issued the Series O Preferred Unit in connection with an acquisition. The Operating Partnership has authorized up to 200,000 4.00% Series P Preferred Units of limited partnership interest, or the Series P Preferred Units, with a liquidation preference of $25.00 per unit. In July 2015, the Company issued 200,000 Series P Preferred Units in conjunction with an acquisition. The Series P Preferred unitholders receive annual dividends of $1.00 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Series P Preferred Units can be redeemed at any time at par for cash at the option of the unitholder. The Operating Partnership has authorized up to 268,000 3.50% Series Q Preferred Units of limited partnership interest, or the Series Q Preferred Units, with a liquidation preference of $25.00 per unit. In July 2015, the Company issued 268,000 Series Q Preferred Units in conjunction with an acquisition. The Series Q Preferred unitholders receive annual dividends of $0.875 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Series Q Preferred Units can be redeemed at any time, at the option of the unitholder, either for cash or are convertible into a number of common units of limited partnership interest in the Operating Partnership equal to (i) the liquidation preference plus accumulated and unpaid distributions on the conversion date divided by (ii) $148.95 . The Operating Partnership has authorized up to 400,000 3.50% Series R Preferred Units of limited partnership interest, or the Series R Preferred Units, with a liquidation preference of $25.00 per unit. In August 2015, the Company issued 400,000 Series R Preferred Units in conjunction with an acquisition. The Series R Preferred unitholders receive annual dividends of $0.875 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Series R Preferred Units can be redeemed at any time, at the option of the unitholder, either for cash or are convertible into a number of common units of limited partnership interest in the Operating Partnership equal to (i) the liquidation preference plus accumulated and unpaid distributions on the conversion date divided by (ii) $154.89 . The Operating Partnership has authorized up to 1,077,280 4.00% Series S Preferred Units of limited partnership interest, or the Series S Preferred Units, with a liquidation preference of $25.00 per unit. In August 2015, the Company issued 1,077,280 Series S Preferred Units in conjunction with an acquisition. The Series S Preferred unitholders receive annual dividends of $1.00 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Series S Preferred Units can be redeemed at any time at par for cash at the option of the unitholder. The Operating Partnership has authorized up to 230,000 2.75% Series T Preferred Units of limited partnership interest, or the Series T Preferred Units, with a liquidation preference of $25.00 per unit. In March 2016, the Company issued 230,000 Series T Preferred Units in conjunction with an acquisition. The Series T Preferred unitholders receive annual dividends of $0.6875 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Series T Preferred Units can be redeemed at any time at par, at the option of the unitholder, either for cash or are convertible into a number of common units of limited partnership interest in the Operating Partnership equal to (i) the liquidation preference plus accumulated and unpaid distributions on the conversion date divided by (ii) $119.02 . The Operating Partnership has authorized up to 680,000 4.50% Series U Preferred Units of limited partnership interest, or the Series U Preferred Units, with a liquidation preference of $25.00 per unit. In March 2016, the Company issued 680,000 Series U Preferred Units in conjunction with an acquisition. The Series U Preferred unitholders initially receive annual dividends of $1.125 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The annual dividend is subject to reduction upon the occurrence of certain circumstances set forth in the terms of the Series U Preferred Units. The minimum annual dividend is $0.75 per unit. The Series U Preferred Units can be redeemed at any time at par for cash at the option of the unitholder. T hrough a consolidated subsidiary, we have authorized up to 109,161 3.50% Series A Preferred Units of limited partnership interest, or the Subsidiary Series A Preferred Units, with a liquidation preference of $1,000.00 per unit. In August 2015, the Company issued 109,161 Subsidiary Series A Preferred Units in conjunction with an acquisition. The Subsidiary Series A Preferred unitholders receive annual dividends of $35.00 per unit paid on a quarterly basis and dividends are cumulative, subject to certain provisions. The Subsidiary Series A Preferred Units can be redeemed at any time, at the option of the unitholder, either for cash or are convertible on a one-for-one basis, into the Series B Preferred Units of limited partnership interest, or the Subsidiary Series B Preferred Units. The Subsidiary Series B Preferred Units can be converted at any time, at the option of the unitholder, into a number of common stock equal to 6.71348 shares of common stock for each Subsidiary Series B Preferred Unit. As of December 31, 2017 , no Subsidiary Series B Preferred Units have been issued. Below is the rollforward analysis of the activity relating to the preferred units in the Operating Partnership as of December 31, 2017 and 2016 (in thousands): December 31, 2017 2016 Balance at beginning of period $ 302,010 $ 282,516 Issuance of preferred units — 22,793 Redemption of preferred units (275 ) (3,299 ) Balance at end of period $ 301,735 $ 302,010

Stockholders' Equity of the Com

Stockholders' Equity of the Company	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Stockholders' Equity of the Company	Stockholders’ Equity of the Company Common Stock Our authorized capital stock consists of 260,000,000 shares, $0.01 par value per share, consisting of 160,000,000 shares of common stock, $0.01 par value per share, 75,000,000 shares of excess stock, at $0.01 par value per share, and 25,000,000 shares of preferred stock, par value $0.01 per share. As of December 31, 2017 , 92,803,299 shares of common stock and no shares of excess stock were issued and outstanding. Stock Repurchase Program In August 2016, our board of directors approved a stock repurchase plan under which we can buy up to $1.0 billion of shares of our common stock. In December 2017, our board of directors authorized an increase to the size of this plan by an additional $500 million of our common stock, bringing it to a total of $1.5 billion of shares. At December 31, 2017 repurchases under the plan were as follows: Period Number of shares purchased Average price paid per share Cumulative number of shares purchased as part of the repurchase plan or programs Maximum approximate dollar value of shares that may yet be purchased under the plan (in millions) (1) First quarter 2017 63,812 $103.84 63,812 $1,493.4 Second quarter 2017 2,384,323 $103.40 2,448,135 $1,246.8 Third quarter 2017 951,866 $101.67 3,400,001 $1,150.0 Fourth quarter 2017 (2) 4,942,410 $100.76 8,342,411 $652.0 (1) Reflective of $1.5 billion plan maximum as of December 31, 2017 . (2) Includes 413,700 shares of common stock repurchased by the Company in December 2017 that were settled in January 2018. At-The-Market Equity Offering Program In July 2011, the Company, along with the Operating Partnership, entered into an "at-the-market" equity offering program, or ATM Program, to sell an aggregate of $250.0 million of our common stock. During the year ended December 31, 2015 , we sold 25,659 shares of our common stock out of the remaining balance of the ATM Program for aggregate net proceeds of $2.8 million . The net proceeds from these offerings were contributed to the Operating Partnership in exchange for 25,659 units of limited partnership interest of the Operating Partnership. In June 2014, the Company, along with the Operating Partnership, entered into an ATM Program to sell an aggregate of $300.0 million of our common stock. During the year ended December 31, 2015 , we sold 895,956 shares of our common stock for aggregate net proceeds of $113.4 million comprising the remaining balance of this ATM Program. The net proceeds from these offerings were contributed to the Operating Partnership in exchange for 895,956 units of limited partnership interest of the Operating Partnership. In March 2015, the Company, along with the Operating Partnership, entered into a new ATM Program to sell an aggregate of $300.0 million of our common stock. The Company did not make any sales of its common stock under an ATM program in the years ended December 31, 2016 and December 31, 2017 . Perpetual Preferred Stock We have 9,200,000 shares of our 6.50% Series I Cumulative Redeemable Preferred Stock, or the Series I Preferred Stock, outstanding with a mandatory liquidation preference of $25.00 per share. The Series I Preferred stockholders receive annual dividends of $1.625 per share paid on a quarterly basis and dividends are cumulative, subject to certain provisions. We are entitled to redeem the Series I Preferred Stock at par for cash at our option. In August 2012, we received $221.9 million in net proceeds from the issuance of the Series I Preferred Stock, which were recorded net of underwriters' discount and issuance costs, and contributed the net proceeds to the Operating Partnership in exchange for 9,200,000 units of 6.50% Series I Cumulative Redeemable Preferred Units of limited partnership interest, or the Series I Preferred Units. Dividend Reinvestment and Stock Purchase Plan In February 2015, the Company filed a registration statement with the SEC for our dividend reinvestment and stock purchase plan, or DRSPP, which automatically became effective upon filing. The Company registered 3,500,000 shares of our common stock under the DRSPP. The DRSPP commenced on September 24, 2001. The following table summarizes SL Green common stock issued, and proceeds received from dividend reinvestments and/or stock purchases under the DRSPP for the year ended December 31, 2017 , 2016 , and 2015 , respectively (in thousands): Year Ended December 31, 2017 2016 2015 Common Stock Shares Issued 2,141 2,687 775,760 Dividend reinvestments/stock purchases under the DRSPP $ 223 $ 277 $ 99,555 Earnings per Share SL Green's earnings per share for the years ended December 31, 2017 , 2016 , and 2015 are computed as follows (in thousands): Year Ended December 31, Numerator 2017 2016 2015 Basic Earnings: Income attributable to SL Green common stockholders $ 86,424 $ 234,946 $ 269,132 Effect of Dilutive Securities: Redemption of units to common shares 3,995 10,136 10,565 Diluted Earnings: Income attributable to SL Green common stockholders $ 90,419 $ 245,082 $ 279,697 Year Ended December 31, Denominator 2017 2016 2015 Basic Shares: Weighted average common stock outstanding 98,571 100,185 99,345 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,556 4,323 3,899 Stock-based compensation plans 276 373 490 Diluted weighted average common stock outstanding 103,403 104,881 103,734 SL Green has excluded 1,092,870 , 774,782 and 263,991 common stock equivalents from the diluted shares outstanding for the years ended December 31, 2017 , 2016 , and 2015 respectively, as they were anti-dilutive.

Partners' Capital of the Operat

Partners' Capital of the Operating Partnership	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity
Partners' Capital of the Operating Partnership	Stockholders’ Equity of the Company Common Stock Our authorized capital stock consists of 260,000,000 shares, $0.01 par value per share, consisting of 160,000,000 shares of common stock, $0.01 par value per share, 75,000,000 shares of excess stock, at $0.01 par value per share, and 25,000,000 shares of preferred stock, par value $0.01 per share. As of December 31, 2017 , 92,803,299 shares of common stock and no shares of excess stock were issued and outstanding. Stock Repurchase Program In August 2016, our board of directors approved a stock repurchase plan under which we can buy up to $1.0 billion of shares of our common stock. In December 2017, our board of directors authorized an increase to the size of this plan by an additional $500 million of our common stock, bringing it to a total of $1.5 billion of shares. At December 31, 2017 repurchases under the plan were as follows: Period Number of shares purchased Average price paid per share Cumulative number of shares purchased as part of the repurchase plan or programs Maximum approximate dollar value of shares that may yet be purchased under the plan (in millions) (1) First quarter 2017 63,812 $103.84 63,812 $1,493.4 Second quarter 2017 2,384,323 $103.40 2,448,135 $1,246.8 Third quarter 2017 951,866 $101.67 3,400,001 $1,150.0 Fourth quarter 2017 (2) 4,942,410 $100.76 8,342,411 $652.0 (1) Reflective of $1.5 billion plan maximum as of December 31, 2017 . (2) Includes 413,700 shares of common stock repurchased by the Company in December 2017 that were settled in January 2018. At-The-Market Equity Offering Program In July 2011, the Company, along with the Operating Partnership, entered into an "at-the-market" equity offering program, or ATM Program, to sell an aggregate of $250.0 million of our common stock. During the year ended December 31, 2015 , we sold 25,659 shares of our common stock out of the remaining balance of the ATM Program for aggregate net proceeds of $2.8 million . The net proceeds from these offerings were contributed to the Operating Partnership in exchange for 25,659 units of limited partnership interest of the Operating Partnership. In June 2014, the Company, along with the Operating Partnership, entered into an ATM Program to sell an aggregate of $300.0 million of our common stock. During the year ended December 31, 2015 , we sold 895,956 shares of our common stock for aggregate net proceeds of $113.4 million comprising the remaining balance of this ATM Program. The net proceeds from these offerings were contributed to the Operating Partnership in exchange for 895,956 units of limited partnership interest of the Operating Partnership. In March 2015, the Company, along with the Operating Partnership, entered into a new ATM Program to sell an aggregate of $300.0 million of our common stock. The Company did not make any sales of its common stock under an ATM program in the years ended December 31, 2016 and December 31, 2017 . Perpetual Preferred Stock We have 9,200,000 shares of our 6.50% Series I Cumulative Redeemable Preferred Stock, or the Series I Preferred Stock, outstanding with a mandatory liquidation preference of $25.00 per share. The Series I Preferred stockholders receive annual dividends of $1.625 per share paid on a quarterly basis and dividends are cumulative, subject to certain provisions. We are entitled to redeem the Series I Preferred Stock at par for cash at our option. In August 2012, we received $221.9 million in net proceeds from the issuance of the Series I Preferred Stock, which were recorded net of underwriters' discount and issuance costs, and contributed the net proceeds to the Operating Partnership in exchange for 9,200,000 units of 6.50% Series I Cumulative Redeemable Preferred Units of limited partnership interest, or the Series I Preferred Units. Dividend Reinvestment and Stock Purchase Plan In February 2015, the Company filed a registration statement with the SEC for our dividend reinvestment and stock purchase plan, or DRSPP, which automatically became effective upon filing. The Company registered 3,500,000 shares of our common stock under the DRSPP. The DRSPP commenced on September 24, 2001. The following table summarizes SL Green common stock issued, and proceeds received from dividend reinvestments and/or stock purchases under the DRSPP for the year ended December 31, 2017 , 2016 , and 2015 , respectively (in thousands): Year Ended December 31, 2017 2016 2015 Common Stock Shares Issued 2,141 2,687 775,760 Dividend reinvestments/stock purchases under the DRSPP $ 223 $ 277 $ 99,555 Earnings per Share SL Green's earnings per share for the years ended December 31, 2017 , 2016 , and 2015 are computed as follows (in thousands): Year Ended December 31, Numerator 2017 2016 2015 Basic Earnings: Income attributable to SL Green common stockholders $ 86,424 $ 234,946 $ 269,132 Effect of Dilutive Securities: Redemption of units to common shares 3,995 10,136 10,565 Diluted Earnings: Income attributable to SL Green common stockholders $ 90,419 $ 245,082 $ 279,697 Year Ended December 31, Denominator 2017 2016 2015 Basic Shares: Weighted average common stock outstanding 98,571 100,185 99,345 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,556 4,323 3,899 Stock-based compensation plans 276 373 490 Diluted weighted average common stock outstanding 103,403 104,881 103,734 SL Green has excluded 1,092,870 , 774,782 and 263,991 common stock equivalents from the diluted shares outstanding for the years ended December 31, 2017 , 2016 , and 2015 respectively, as they were anti-dilutive.
SL Green Operating Partnership
Stockholders' Equity
Partners' Capital of the Operating Partnership	Partners' Capital of the Operating Partnership The Company is the sole general partner of the Operating Partnership and at December 31, 2017 owned 92,803,299 general and limited partnership interests in the Operating Partnership and 9,200,000 Series I Preferred Units. Partnership interests in the Operating Partnership are denominated as “common units of limited partnership interest” (also referred to as “OP Units”) or “preferred units of limited partnership interest” (also referred to as “Preferred Units”). All references to OP Units and Preferred Units outstanding exclude such units held by the Company. A holder of an OP Unit may present such OP Unit to the Operating Partnership for redemption at any time (subject to restrictions agreed upon at the issuance of OP Units to particular holders that may restrict such right for a period of time, generally one year from issuance). Upon presentation of an OP Unit for redemption, the Operating Partnership must redeem such OP Unit in exchange for the cash equal to the then value of a share of common stock of the Company, except that the Company may, at its election, in lieu of cash redemption, acquire such OP Unit for one share of common stock. Because the number of shares of common stock outstanding at all times equals the number of OP Units that the Company owns, one share of common stock is generally the economic equivalent of one OP Unit, and the quarterly distribution that may be paid to the holder of an OP Unit equals the quarterly dividend that may be paid to the holder of a share of common stock. Each series of Preferred Units makes a distribution that is set in accordance with an amendment to the partnership agreement of the Operating Partnership. Preferred Units may also be convertible into OP Units at the election of the holder thereof or the Company, subject to the terms of such Preferred Units. Net income (loss) allocated to the preferred unitholders and common unitholders reflects their pro rata share of net income (loss) and distributions. Limited Partner Units As of December 31, 2017 , limited partners other than SL Green owned 4.58% , or 4,452,979 common units, of the Operating Partnership. Preferred Units Preferred units not owned by SL Green are further described in Note 11, “Noncontrolling Interests on the Company’s Consolidated Financial Statements - Preferred Units of Limited Partnership Interest in the Operating Partnership.” Earnings per Unit The Operating Partnership's earnings per unit for the years ended December 31, 2017 , 2016 , and 2015 respectively are computed as follows (in thousands): Year Ended December 31, Numerator 2017 2016 2015 Basic and Diluted Earnings: Income attributable to SLGOP common unitholders $ 90,419 $ 245,082 $ 279,697 Year Ended December 31, Denominator 2017 2016 2015 Basic units: Weighted average common units outstanding 103,127 104,508 103,244 Effect of Dilutive Securities: Stock-based compensation plans 276 373 490 Diluted weighted average common units outstanding 103,403 104,881 103,734 The Operating Partnership has excluded 1,092,870 , 774,782 , and 263,991 common unit equivalents from the diluted units outstanding for the years ended December 31, 2017 , 2016 , and 2015 respectively, as they were anti-dilutive.

Share-based Compensation

Share-based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation	Share-based Compensation We have stock-based employee and director compensation plans. Our employees are compensated through the Operating Partnership. Under each plan, whenever the Company issues common or preferred stock, the Operating Partnership issues an equivalent number of units of limited partnership interest of a corresponding class to the Company. Fourth Amended and Restated 2005 Stock Option and Incentive Plan The Fourth Amended and Restated 2005 Stock Option and Incentive Plan, or the 2005 Plan, was approved by the Company's board of directors in April 2016 and its stockholders in June 2016 at the Company's annual meeting of stockholders. The 2005 Plan authorizes the issuance of stock options, stock appreciation rights, unrestricted and restricted stock, phantom shares, dividend equivalent rights, cash-based awards and other equity-based awards. Subject to adjustments upon certain corporate transactions or events, awards with respect to up to a maximum of 27,030,000 fungible units may be granted under the 2005 Plan. Currently, different types of awards count against the limit on the number of fungible units differently, with (1) full-value awards (i.e., those that deliver the full value of the award upon vesting, such as restricted stock) counting as 3.74 Fungible Units per share subject to such awards, (2) stock options, stock appreciation rights and other awards that do not deliver full value and expire five years from the date of grant counting as 0.73 fungible units per share subject to such awards, and (3) all other awards (e.g., ten -year stock options) counting as 1.0 fungible units per share subject to such awards. Awards granted under the 2005 Plan prior to the approval of the fourth amendment and restatement in June 2016 continue to count against the fungible unit limit based on the ratios that were in effect at the time such awards were granted, which may be different than the current ratios. As a result, depending on the types of awards issued, the 2005 Plan may result in the issuance of more or less than 27,030,000 shares. If a stock option or other award granted under the 2005 Plan expires or terminates, the common stock subject to any portion of the award that expires or terminates without having been exercised or paid, as the case may be, will again become available for the issuance of additional awards. Shares of our common stock distributed under the 2005 Plan may be treasury shares or authorized but unissued shares. Currently, unless the 2005 Plan has been previously terminated by the Company's board of directors, new awards may be granted under the 2005 Plan until June 2, 2026, which is the tenth anniversary of the date that the 2005 Plan was most recently approved by the Company's stockholders. As of December 31, 2017 , 8.3 million fungible units were available for issuance under the 2005 Plan after reserving for shares underlying outstanding restricted stock units, phantom stock units granted pursuant to our Non-Employee Directors' Deferral Program and LTIP Units. Options are granted under the plan with an exercise price at the fair market value of the Company's common stock on the date of grant and, subject to employment, generally expire five or ten years from the date of grant, are not transferable other than on death, and generally vest in one to five years commencing one year from the date of grant. We have also granted Class O LTIP Units, which are a class of LTIP Units in the Operating Partnership structured to provide economics similar to those of stock options. Class O LTIP Units, once vested, may be converted, at the election of the holder, into a number of common units of the Operating Partnership per Class O LTIP Unit determined by the increase in value of a share of the Company’s common stock at the time of conversion over a participation threshold, which equals the fair market value of a share of the Company’s common stock at the time of grant. Class O LTIP Units are entitled to distributions, subject to vesting, equal per unit to 10% of the per unit distributions paid with respect to the common units of the Operating Partnership. The fair value of each stock option or LTIP Unit granted is estimated on the date of grant using the Black-Scholes option pricing model based on historical information with the following weighted average assumptions for grants during the years ended December 31, 2017 , 2016 , and 2015 . 2017 2016 2015 Dividend yield 2.51 % 2.37 % 1.97 % Expected life 4.4 years 3.7 years 3.6 years Risk-free interest rate 1.73 % 1.57 % 1.43 % Expected stock price volatility 28.10 % 26.76 % 32.34 % A summary of the status of the Company's stock options as of December 31, 2017 , 2016 , and 2015 and changes during the years ended December 31, 2017 , 2016 , and 2015 are as follows: 2017 2016 2015 Options Outstanding Weighted Average Exercise Price Options Outstanding Weighted Average Exercise Price Options Weighted Balance at beginning of year $ 1,737,213 $ 98.44 $ 1,595,007 $ 95.52 $ 1,462,726 $ 87.98 Granted 174,000 105.66 445,100 105.86 389,836 112.54 Exercised (292,193 ) 81.07 (192,875 ) 76.90 (217,438 ) 74.69 Lapsed or canceled (70,301 ) 121.68 (110,019 ) 123.86 (40,117 ) 98.61 Balance at end of year $ 1,548,719 $ 101.48 $ 1,737,213 $ 98.44 $ 1,595,007 $ 95.52 Options exercisable at end of year 800,902 $ 94.33 748,617 $ 87.72 589,055 $ 89.85 Weighted average fair value of options granted during the year $ 3,816,652 $ 8,363,036 $ 9,522,613 All options were granted with strike prices ranging from $ 20.67 to $ 137.18 . The remaining weighted average contractual life of the options outstanding was 3.6 years and the remaining average contractual life of the options exercisable was 3.1 years. During the years ended December 31, 2017 , 2016 , and 2015 , we recognized compensation expense for these options of $7.8 million , $8.9 million , and $8.0 million , respectively. As of December 31, 2017 , there was $8.6 million of total unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted average period of 1.5 years. Stock-based Compensation Effective January 1, 1999, the Company implemented a deferred compensation plan, or the Deferred Plan, where shares issued under the Deferred Plan were granted to certain employees, including our executives and vesting will occur annually upon the completion of a service period or our meeting established financial performance criteria. Annual vesting occurs at rates ranging from 15% to 35% once performance criteria are reached. A summary of the Company's restricted stock as of December 31, 2017 , 2016 , and 2015 and charges during the years ended December 31, 2017 , 2016 , and 2015 are as follows: 2017 2016 2015 Balance at beginning of year 3,202,031 3,137,881 3,000,979 Granted 96,185 98,800 143,053 Canceled — (34,650 ) (6,151 ) Balance at end of year 3,298,216 3,202,031 3,137,881 Vested during the year 95,736 83,822 87,081 Compensation expense recorded $ 9,809,749 $ 7,153,966 $ 7,540,747 Weighted average fair value of restricted stock granted during the year $ 9,905,986 $ 10,650,077 $ 16,061,201 The fair value of restricted stock that vested during the years ended December 31, 2017 , 2016 , and 2015 was $9.4 million , $7.6 million and $7.4 million , respectively. As of December 31, 2017 , there was $21.1 million of total unrecognized compensation cost related to restricted stock, which is expected to be recognized over a weighted average period of 2.2 years . For the years ended December 31, 2017 , 2016 , and 2015 , $7.2 million , $6.0 million , and $6.5 million , respectively, was capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options. We granted LTIP Units, which include bonus, time-based and performance based awards, with a fair value of $20.5 million and $34.9 million during the years ended December 31, 2017 and 2016 , respectively. The grant date fair value of the LTIP Unit awards was calculated in accordance with ASC 718. A third party consultant determined the fair value of the LTIP Units to have a discount from our common stock price. The discount was calculated by considering the inherent uncertainty that the LTIP Units will reach parity with other common partnership units and the illiquidity due to transfer restrictions. As of December 31, 2017 , there was $4.6 million of total unrecognized compensation expense related to the time-based and performance based LTIP Unit awards, which is expected to be recognized over a weighted average period of 1.5 years. During the years ended December 31, 2017 , 2016 , and 2015 , we recorded compensation expense related to bonus, time-based and performance based LTIP Unit awards of $26.1 million , $26.5 million, and $30.2 million , respectively. 2011 Outperformance Plan In August 2011, the compensation committee of the Company's board of directors approved the general terms of the SL Green Realty Corp. 2011 Outperformance Plan, or the 2011 Outperformance Plan. Participants in the 2011 Outperformance Plan could earn, in the aggregate, up to $85.0 million of LTIP Units in the Operating Partnership based on our total return to stockholders for the three-year period beginning September 1, 2011. Under the 2011 Outperformance Plan, participants were entitled to share in a "performance pool" comprised of LTIP Units with a value equal to 10% of the amount by which our total return to stockholders during the three -year period exceeded a cumulative total return to stockholders of 25% , subject to the maximum of $85.0 million of LTIP Units; provided that if maximum performance was achieved, one-third of each award could be earned at any time after the beginning of the second year and an additional one-third of each award could be earned at any time after the beginning of the third year. LTIP Units earned under the 2011 Outperformance Plan were subject to vesting requirements, with 50% of any awards earned vesting on August 31, 2014 and the remaining 50% vesting on August 31, 2015, based on continued employment with us through such dates. Participants were not entitled to distributions with respect to LTIP Units granted under the 2011 Outperformance Plan unless and until they were earned. For LTIP Units that were earned, each participant was also entitled to the distributions that would have been paid had the number of earned LTIP Units been issued at the beginning of the performance period, with such distributions being paid in the form of additional LTIP Units. Thereafter, distributions are paid currently with respect to all earned LTIP Units, whether vested or unvested. In June 2014, the compensation committee determined that maximum performance had been achieved during the third year of the performance period and, accordingly, 560,908 LTIP Units, representing two-thirds of each award, were earned, subject to vesting, under the 2011 Outperformance Plan. In September 2014, the compensation committee determined that maximum performance had been achieved for the full three -year performance period and, accordingly, 280,454 LTIP units, representing the final third of each award, were earned, subject to vesting, under the 2011 Outperformance Plan. The cost of the 2011 Outperformance Plan ( $26.7 million , subject to forfeitures) was amortized into earnings through the final vesting period. We recorded no compensation expense during the year ended December 31, 2017 , no compensation expense during the year ended December 31, 2016 , and compensation expense of $4.5 million during the year ended December 31, 2015 , related to the 2011 Outperformance Plan. 2014 Outperformance Plan In August 2014, the compensation committee of the Company's board of directors approved the general terms of the SL Green Realty Corp. 2014 Outperformance Plan, or the 2014 Outperformance Plan. Participants in the 2014 Outperformance Plan could earn, in the aggregate, up to 610,000 LTIP Units in our Operating Partnership based on our total return to stockholders for the three -year period beginning September 1, 2014. Under the 2014 Outperformance Plan, two-thirds of the LTIP Units were subject to performance based vesting based on the Company’s absolute total return to stockholders and one-third of the LTIP Units were subject to performance based vesting based on relative total return to stockholders compared to the constituents of the MSCI REIT Index. LTIP Units earned under the 2014 Outperformance Plan were to be subject to continued vesting requirements, with 50% of any awards earned vesting on August 31, 2017 and the remaining 50% vesting on August 31, 2018, subject to continued employment with us through such dates. Participants were not entitled to distributions with respect to LTIP Units granted under the 2014 Outperformance Plan unless and until they are earned. If LTIP Units were earned, each participant would have been entitled to the distributions that would have been paid had the number of earned LTIP Units been issued at the beginning of the performance period, with such distributions being paid in the form of cash or additional LTIP Units. Thereafter, distributions were to be paid currently with respect to all earned LTIP Units, whether vested or unvested. Based on our performance, none of the LTIP Units granted under the 2014 Outperformance Plan were earned pursuant to the terms of the 2014 Outperformance Plan, and all units issued were forfeited in 2017. The cost of the 2014 Outperformance Plan ( $27.9 million subject to forfeitures), based on the portion of the 2014 Outperformance Plan granted prior to termination, was amortized into earnings through December 31, 2017. We recorded compensation expense of $13.6 million , $8.4 million , and $5.9 million during the years ended December 31, 2017 , 2016 , and 2015 , respectively, related to the 2014 Outperformance Plan. Deferred Compensation Plan for Directors Under our Non-Employee Director's Deferral Program, which commenced July 2004, the Company's non-employee directors may elect to defer up to 100% of their annual retainer fee, chairman fees, meeting fees and annual stock grant. Unless otherwise elected by a participant, fees deferred under the program shall be credited in the form of phantom stock units. The program provides that a director's phantom stock units generally will be settled in an equal number of shares of common stock upon the earlier of (i) the January 1 coincident with or the next following such director's termination of service from the Board of Directors or (ii) a change in control by us, as defined by the program. Phantom stock units are credited to each non-employee director quarterly using the closing price of our common stock on the first business day of the respective quarter. Each participating non-employee director is also credited with dividend equivalents or phantom stock units based on the dividend rate for each quarter, which are either paid in cash currently or credited to the director’s account as additional phantom stock units. During the year ended December 31, 2017 , 12,727 phantom stock units were earned and 9,509 shares of common stock were issued to our board of directors. We recorded compensation expense of $2.4 million during the year ended December 31, 2017 related to the Deferred Compensation Plan. As of December 31, 2017 , there were 99,853 phantom stock units outstanding pursuant to our Non-Employee Director's Deferral Program. Employee Stock Purchase Plan In 2007, the Company's board of directors adopted the 2008 Employee Stock Purchase Plan, or ESPP, to encourage our employees to increase their efforts to make our business more successful by providing equity-based incentives to eligible employees. The ESPP is intended to qualify as an "employee stock purchase plan" under Section 423 of the Code, and has been adopted by the board to enable our eligible employees to purchase the Company's shares of common stock through payroll deductions. The ESPP became effective on January 1, 2008 with a maximum of 500,000 shares of the common stock available for issuance, subject to adjustment upon a merger, reorganization, stock split or other similar corporate change. The Company filed a registration statement on Form S-8 with the SEC with respect to the ESPP. The common stock is offered for purchase through a series of successive offering periods. Each offering period will be three months in duration and will begin on the first day of each calendar quarter, with the first offering period having commenced on January 1, 2008. The ESPP provides for eligible employees to purchase the common stock at a purchase price equal to 85% of the lesser of (1) the market value of the common stock on the first day of the offering period or (2) the market value of the common stock on the last day of the offering period. The ESPP was approved by our stockholders at our 2008 annual meeting of stockholders. As of December 31, 2017 , 104,597 shares of our common stock had been issued under the ESPP.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Accumulated Other Comprehensive Income	Accumulated Other Comprehensive Income The following tables set forth the changes in accumulated other comprehensive income (loss) by component as of December 31, 2017 , 2016 and 2015 (in thousands): Net unrealized gain on derivative instruments ( 1 ) SL Green’s share of joint venture net unrealized gain on derivative instruments ( 2 ) Net unrealized gain on marketable securities Total Balance at December 31, 2014 $ (9,498 ) $ (95 ) $ 2,613 $ (6,980 ) Other comprehensive loss before reclassifications (11,143 ) (1,714 ) (610 ) (13,467 ) Amounts reclassified from accumulated other comprehensive income 10,481 1,217 — 11,698 Balance at December 31, 2015 (10,160 ) (592 ) 2,003 (8,749 ) Other comprehensive income before reclassifications 13,534 1,160 3,517 18,211 Amounts reclassified from accumulated other comprehensive income 9,222 3,453 — 12,675 Balance at December 31, 2016 12,596 4,021 5,520 22,137 Other comprehensive (loss) income before reclassifications (1,618 ) 233 (1,348 ) (2,733 ) Amounts reclassified from accumulated other comprehensive income 1,564 766 (3,130 ) (800 ) Balance at December 31, 2017 $ 12,542 $ 5,020 $ 1,042 $ 18,604 (1) Amount reclassified from accumulated other comprehensive income (loss) is included in interest expense in the respective consolidated statements of operations. As of December 31, 2017 and 2016 , the deferred net losses from these terminated hedges, which is included in accumulated other comprehensive loss relating to net unrealized loss on derivative instrument, was $3.2 million and $7.1 million , respectively. (2) Amount reclassified from accumulated other comprehensive income (loss) is included in equity in net income from unconsolidated joint ventures in the respective consolidated statements of operations.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements We are required to disclose fair value information with regard to our financial instruments, whether or not recognized in the consolidated balance sheets, for which it is practical to estimate fair value. The FASB guidance defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. We measure and/or disclose the estimated fair value of financial assets and liabilities based on a hierarchy that distinguishes between market participant assumptions based on market data obtained from sources independent of the reporting entity and the reporting entity’s own assumptions about market participant assumptions. This hierarchy consists of three broad levels: Level 1 - quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the measurement date; Level 2 - inputs other than quoted prices included within Level 1, that are observable for the asset or liability, either directly or indirectly; and Level 3 - unobservable inputs for the asset or liability that are used when little or no market data is available. We follow this hierarchy for our assets and liabilities measured at fair value on a recurring and nonrecurring basis. In instances in which the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level of input that is significant to the fair value measurement in its entirety. Our assessment of the significance of the particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability. The following tables set forth the assets and liabilities that we measure at fair value on a recurring and non-recurring basis by their levels in the fair value hierarchy at December 31, 2017 and 2016 (in thousands): December 31, 2017 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 28,579 $ — $ 28,579 $ — Interest rate cap and swap agreements (included in other assets) $ 16,692 $ — $ 16,692 $ — December 31, 2016 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 85,110 $ 48,315 $ 36,795 $ — Interest rate cap and swap agreements (included in other assets) $ 21,090 $ — $ 21,090 $ — Liabilities: Interest rate cap and swap agreements (included in accrued interest payable and other liabilities) $ 1 $ — $ 1 $ — We determine other than temporary impairment in real estate investments and debt and preferred equity investments, including intangibles primarily utilizing cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as sales comparison approach, which utilizes comparable sales, listings and sales contracts. All of which are classified as Level 3 inputs. As of December 31, 2017 , we held notes receivable totaling $250.0 million , which were purchased at par, and were in maturity default at the time of acquisition. In August 2017, the Company determined that it was probable that the loans would not be repaid in full and therefore, the loans were put on non-accrual status. The loans had an outstanding balance including accrued interest of $259.3 million at the time that they were put on non accrual status. The Company has initiated proceedings to foreclose on the property, and expects to take control of the property unless the buyer is able to repay the principal and interest, including default interest and fees, on the notes receivable in full prior to the completion of the foreclosure process. We believe the collateral value is sufficient to recover the carrying amounts of the notes receivable. The marketable securities classified as Level 1 were derived from quoted prices in active markets. The valuation technique used to measure the fair value of the marketable securities classified as Level 2 were valued based on quoted market prices or model driven valuations using the significant inputs derived from or corroborated by observable market data. Marketable securities in an unrealized loss position are not considered to be other than temporarily impaired. We do not intend to sell these securities and it is not more likely than not that we will be required to sell the investments before recovery of their amortized cost bases. The fair value of derivative instruments is based on current market data received from financial sources that trade such instruments and are based on prevailing market data and derived from third party proprietary models based on well-recognized financial principles and reasonable estimates about relevant future market conditions, which are classified as Level 2 inputs. The financial assets and liabilities that are not measured at fair value on our consolidated balance sheets include cash and cash equivalents, restricted cash, accounts receivable, accounts payable and accrued expenses, debt and preferred equity investments, mortgages and other loans payable and other secured and unsecured debt. The carrying amount of cash and cash equivalents, restricted cash, accounts receivable, and accounts payable and accrued expenses reported in our consolidated balance sheets approximates fair value due to the short term nature of these instruments. The fair value of debt and preferred equity investments, which is classified as Level 3, is estimated by discounting the future cash flows using current interest rates at which similar loans with the same maturities would be made to borrowers with similar credit ratings. The fair value of borrowings, which is classified as Level 3, is estimated by discounting the contractual cash flows of each debt instrument to their present value using adjusted market interest rates, which is provided by a third-party specialist. The following table provides the carrying value and fair value of these financial instruments as of December 31, 2017 and December 31, 2016 (in thousands): December 31, 2017 December 31, 2016 Carrying Value (1) Fair Value Carrying Value (1) Fair Value Debt and preferred equity investments $ 2,114,041 (2) $ 1,640,412 (2) Fixed rate debt $ 4,305,165 $ 4,421,866 $ 5,452,084 $ 5,722,494 Variable rate debt 1,605,431 1,612,224 1,105,585 1,110,110 $ 5,910,596 $ 6,034,090 $ 6,557,669 $ 6,832,604 (1) Amounts exclude net deferred financing costs. (2) At December 31, 2017 , debt and preferred equity investments had an estimated fair value ranging between $2.1 billion and $2.3 billion . At December 31, 2016 , debt and preferred equity investments had an estimated fair value ranging between $1.6 billion and $1.8 billion . Disclosure about fair value of financial instruments was based on pertinent information available to us as of December 31, 2017 and 2016 . Although we are not aware of any factors that would significantly affect the reasonable fair value amounts, such amounts have not been comprehensively revalued for purposes of these financial statements since that date and current estimates of fair value may differ significantly from the amounts presented herein.

Financial Instruments_ Derivati

Financial Instruments: Derivatives and Hedging	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Financial Instruments: Derivatives and Hedging	Financial Instruments: Derivatives and Hedging In the normal course of business, we use a variety of commonly used derivative instruments, such as interest rate swaps, caps, collar and floors, to manage, or hedge interest rate risk. We hedge our exposure to variability in future cash flows for forecasted transactions in addition to anticipated future interest payments on existing debt. We recognize all derivatives on the balance sheets at fair value. Derivatives that are not hedges are adjusted to fair value through earnings. If a derivative is a hedge, depending on the nature of the hedge, changes in the fair value of the derivative will either be offset against the change in fair value of the hedge asset, liability, or firm commitment through earnings, or recognized in other comprehensive income until the hedged item is recognized in earnings. The ineffective portion of a derivative's change in fair value will be immediately recognized in earnings. Reported net income and equity may increase or decrease prospectively, depending on future levels of interest rates and other variables affecting the fair values of derivative instruments and hedged items, but will have no effect on cash flows. Currently, all of our designated derivative instruments are effective hedging instruments. The following table summarizes the notional value at inception and fair value of our consolidated derivative financial instruments at December 31, 2017 based on Level 2 information. The notional value is an indication of the extent of our involvement in these instruments at that time, but does not represent exposure to credit, interest rate or market risks (amounts in thousands). Notional Value Strike Rate Effective Date Expiration Date Balance Sheet Location Fair Value Interest Rate Swap $ 200,000 1.131 % July 2016 July 2023 Other Assets $ 10,747 Interest Rate Swap 100,000 1.161 % July 2016 July 2023 Other Assets 5,217 Interest Rate Swap 21,394 12.000 % January 2017 January 2019 Other Assets 167 Interest Rate Cap 137,500 4.000 % September 2017 September 2019 Other Assets 2 Interest Rate Swap 100,000 1.928 % December 2017 November 2020 Other Assets 288 Interest Rate Swap 100,000 1.934 % December 2017 November 2020 Other Assets 271 $ 16,692 During the years ended December 31, 2017 , 2016 , and 2015 , we recorded a $0.5 million loss, a $0.5 million gain, and a $0.1 million gain, respectively, on the changes in the fair value, which is included in interest expense in the consolidated statements of operations. The Company has agreements with each of its derivative counterparties that contain a provision where if the Company either defaults or is capable of being declared in default on any of its indebtedness, then the Company could also be declared in default on its derivative obligations. As of December 31, 2017 , the fair value of derivatives in a net liability position including accrued interest but excluding any adjustment for nonperformance risk related to these agreements was zero . As of December 31, 2017 , the Company has not posted any collateral related to these agreements and was not in breach of any agreement provisions. If the Company had breached any of these provisions, it could have been required to settle its obligations under the agreements at their aggregate termination value of zero at December 31, 2017 . Gains and losses on terminated hedges are included in accumulated other comprehensive income, and are recognized into earnings over the term of the related mortgage obligation. Over time, the realized and unrealized gains and losses held in accumulated other comprehensive income will be reclassified into earnings as an adjustment to interest expense in the same periods in which the hedged interest payments affect earnings. We estimate that $0.5 million of the current balance held in accumulated other comprehensive income will be reclassified into interest expense and $(0.3) million of the portion related to our share of joint venture accumulated other comprehensive income will be reclassified into equity in net income from unconsolidated joint ventures within the next 12 months. The following table presents the effect of our derivative financial instruments and our share of our joint ventures' derivative financial instruments that are designated and qualify as hedging instruments on the consolidated statements of operations for the years ended December 31, 2017 , 2016 , and 2015 , respectively (in thousands): Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion) Location of (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion) Location of (Loss) Gain Recognized in Income on Derivative Amount of (Loss) Gain Recognized into Income (Ineffective Portion) Year Ended Year Ended Year Ended Derivative 2017 2016 2015 2017 2016 2015 2017 2016 2015 Interest Rate Swaps/Caps $ (2,282 ) $ 14,616 $ (11,607 ) Interest expense $ 1,821 $ 9,521 $ 10,892 Interest expense $ 5 $ (28 ) $ (422 ) Share of unconsolidated joint ventures' derivative instruments (200 ) 2,012 (1,779 ) Equity in net income from unconsolidated joint ventures 1,035 1,981 1,265 Equity in net income from unconsolidated joint ventures 55 785 (19 ) $ (2,482 ) $ 16,628 $ (13,386 ) $ 2,856 $ 11,502 $ 12,157 $ 60 $ 757 $ (441 )

Rental Income

Rental Income	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Rental Income	Rental Income The Operating Partnership is the lessor and the sublessor to tenants under operating leases with expiration dates ranging from January 1, 2018 to 2064. The minimum rental amounts due under the leases are generally either subject to scheduled fixed increases or adjustments. The leases generally also require that the tenants reimburse us for increases in certain operating costs and real estate taxes above their base year costs. Approximate future minimum rents to be received over the next five years and thereafter for non-cancelable operating leases in effect at December 31, 2017 for the consolidated properties, including consolidated joint venture properties, and our share of unconsolidated joint venture properties are as follows (in thousands): Consolidated Properties Unconsolidated Properties 2018 $ 901,092 $ 433,764 2019 865,254 386,564 2020 790,714 424,201 2021 657,283 426,078 2022 558,993 414,889 Thereafter 3,339,829 3,102,309 $ 7,113,165 $ 5,187,805

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Benefit Plans	Benefit Plans The building employees are covered by multi-employer defined benefit pension plans and post-retirement health and welfare plans. We participate in the Building Service 32BJ, or Union, Pension Plan and Health Plan. The Pension Plan is a multi-employer, non-contributory defined benefit pension plan that was established under the terms of collective bargaining agreements between the Service Employees International Union, Local 32BJ, the Realty Advisory Board on Labor Relations, Inc. and certain other employees. This Pension Plan is administered by a joint board of trustees consisting of union trustees and employer trustees and operates under employer identification number 13-1879376. The Pension Plan year runs from July 1 to June 30. Employers contribute to the Pension Plan at a fixed rate on behalf of each covered employee. Separate actuarial information regarding such pension plans is not made available to the contributing employers by the union administrators or trustees, since the plans do not maintain separate records for each reporting unit. However, on September 28, 2015, and September 28, 2016, and September 28, 2017, the actuary certified that for the plan years beginning July 1, 2015, July 1, 2016, and July 1, 2017, the Pension Plan was in critical status under the Pension Protection Act of 2006. The Pension Plan trustees adopted a rehabilitation plan consistent with this requirement. No surcharges have been paid to the Pension Plan as of December 31, 2017 . For the Pension Plan years ended June 30, 2017 , 2016 , and 2015 , the plan received contributions from employers totaling $257.8 million , $249.5 million , and $221.9 million . Our contributions to the Pension Plan represent less than 5.0% of total contributions to the plan. The Health Plan was established under the terms of collective bargaining agreements between the Union, the Realty Advisory Board on Labor Relations, Inc. and certain other employers. The Health Plan provides health and other benefits to eligible participants employed in the building service industry who are covered under collective bargaining agreements, or other written agreements, with the Union. The Health Plan is administered by a Board of Trustees with equal representation by the employers and the Union and operates under employer identification number 13-2928869. The Health Plan receives contributions in accordance with collective bargaining agreements or participation agreements. Generally, these agreements provide that the employers contribute to the Health Plan at a fixed rate on behalf of each covered employee. For the Health Plan years ended, June 30, 2017 , 2016 , and 2015 , the plan received contributions from employers totaling $1.3 billion , $1.2 billion and $1.1 billion , respectively. Our contributions to the Health Plan represent less than 5.0% of total contributions to the plan. Contributions we made to the multi-employer plans for the years ended December 31, 2017 , 2016 and 2015 are included in the table below (in thousands): Benefit Plan 2017 2016 2015 Pension Plan $ 3,856 $ 3,979 $ 2,732 Health Plan 11,426 11,530 8,736 Other plans 1,463 1,583 5,716 Total plan contributions $ 16,745 $ 17,092 $ 17,184 401(K) Plan In August 1997, we implemented a 401(K) Savings/Retirement Plan, or the 401(K) Plan, to cover eligible employees of ours, and any designated affiliate. The 401(K) Plan permits eligible employees to defer up to 15% of their annual compensation, subject to certain limitations imposed by the Code. The employees' elective deferrals are immediately vested and non-forfeitable upon contribution to the 401(K) Plan. During 2003, we amended our 401(K) Plan to provide for discretionary matching contributions only. For 2017 , 2016 and 2015 , a matching contribution equal to 50% of the first 6% of annual compensation was made. For the year ended December 31, 2017 , we made a matching contribution of $728,782 . For the years ended December 31, 2016 and 2015 , we made matching contributions of $566,000 and $550,000 , respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings As of December 31, 2017 , the Company and the Operating Partnership were not involved in any material litigation nor, to management's knowledge, was any material litigation threatened against us or our portfolio which if adversely determined could have a material adverse impact on us. Environmental Matters Our management believes that the properties are in compliance in all material respects with applicable Federal, state and local ordinances and regulations regarding environmental issues. Management is not aware of any environmental liability that it believes would have a materially adverse impact on our financial position, results of operations or cash flows. Management is unaware of any instances in which it would incur significant environmental cost if any of our properties were sold. Employment Agreements We have entered into employment agreements with certain executives, which expire between December 2018 and February 2020. The minimum cash-based compensation, including base salary and guaranteed bonus payments, associated with these employment agreements total $5.4 million for 2018. In addition these employment agreements provide for deferred compensation awards based on our stock price and which were valued at $1.6 million on the grant date. The value of these awards may change based on fluctuations in our stock price. Insurance We maintain “all-risk” property and rental value coverage (including coverage regarding the perils of flood, earthquake and terrorism, excluding nuclear, biological, chemical, and radiological terrorism ("NBCR")), within three property insurance programs and liability insurance. Separate property and liability coverage may be purchased on a stand-alone basis for certain assets, such as the development of One Vanderbilt. Additionally, our captive insurance company, Belmont Insurance Company, or Belmont, provides coverage for NBCR terrorist acts above a specified trigger, although if Belmont is required to pay a claim under our insurance policies, we would ultimately record the loss to the extent of Belmont's required payment. However, there is no assurance that in the future we will be able to procure coverage at a reasonable cost. Further, if we experience losses that are uninsured or that exceed policy limits, we could lose the capital invested in the damaged properties as well as the anticipated future cash flows from those properties. Additionally, our debt instruments contain customary covenants requiring us to maintain insurance and we could default under debt our instruments if the cost and/or availability of certain types of insurance make it impractical or impossible to comply with such covenants relating to insurance. Belmont provides coverage solely on properties owned by the Company or its affiliates. Furthermore, with respect to certain of our properties, including properties held by joint ventures, or subject to triple net leases, insurance coverage is obtained by a third-party and we do not control the coverage. While we may have agreements with such third parties to maintain adequate coverage and we monitor these policies, such coverage ultimately may not be maintained or adequately cover our risk of loss. Belmont had loss reserves of $5.5 million and $6.3 million as of December 31, 2017 and 2016 , respectively. Capital and Ground Leases Arrangements In 2015, we entered into a ground lease for the land and building located at 30 East 40th Street with a lease term ending in August 2114. Based on our evaluation of the arrangement under ASC 840, land was estimated to be approximately 63.6% of the fair market value of the property. The portion attributable to land was classified as operating lease with an expiration date of 2114 ( $76.0 million total over the lease term attributed to ground rent) and the remainder as a capital lease in the amount of $20.0 million . The property located at 420 Lexington Avenue operates under a ground lease ( $10.9 million of ground rent annually through December 2019, $11.2 million of ground rent annually through December 2029, and $12.3 million annually afterwards, subject to a one-time adjustment based on 6% of the fair value of the land) with an expiration date of 2050 and two options to renew for an additional 35 years. The property located at 1080 Amsterdam Avenue operates under a ground and capital lease with an expiration date of 2111 ( $41.6 million total over the lease term attributed to ground rent). Land was estimated to be 40.0% of the fair market value of the property, which was classified as an operating lease. The remainder was classified as a capital lease. The property located at 711 Third Avenue operates under an operating sub-lease with an expiration date of 2033 and five options to renew for an additional 10 years each. The ground rent was reset in July 2011. Following the reset, we are responsible for ground rent payments of $5.25 million annually through July 2016 and then $5.5 million annually thereafter on the 50% portion of the fee that we do not own. The property located at 461 Fifth Avenue operates under a ground lease ( $2.1 million of ground rent annually) with an expiration date of 2027 and two options to renew for an additional 21 years each, followed by a third option for 15 years. We also have an option to purchase the fee position for a fixed price on a specific date. The property located at 625 Madison Avenue operates under a ground lease ( $4.6 million of ground rent annually) with an expiration date of 2022 and two options to renew for an additional 23 years. The property located at 1185 Avenue of the Americas operates under a ground lease ( $6.9 million of ground rent annually) with an expiration date of 2043 and an option to renew for an additional 23 years. The property located at 1055 Washington Boulevard operates under a ground lease ( $0.6 million of ground rent annually) with an expiration date of 2090. The following is a schedule of future minimum lease payments under capital leases and non-cancellable operating leases with initial terms in excess of one year as of December 31, 2017 (in thousands): Capital lease Non-cancellable operating leases 2018 $ 2,387 $ 31,049 2019 2,411 31,066 2020 2,620 31,436 2021 2,794 31,628 2022 2,794 29,472 Thereafter 819,894 703,254 Total minimum lease payments $ 832,900 $ 857,905 Amount representing interest (790,057 ) Capital lease obligations $ 42,843

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Information	Segment Information The Company is a REIT engaged in all aspects of property ownership and management including investment, leasing operations, capital improvements, development, redevelopment, financing, construction and maintenance in the New York metropolitan area and have two reportable segments, real estate and debt and preferred equity. We evaluate real estate performance and allocate resources based on earnings contribution to income from continuing operations. The primary sources of revenue are generated from tenant rents and escalations and reimbursement revenue. Real estate property operating expenses consist primarily of security, maintenance, utility costs, real estate taxes and ground rent expense (at certain applicable properties). See Note 5, "Debt and Preferred Equity Investments," for additional details on our debt and preferred equity investments. Selected results of operations for the years ended December 31, 2017 , 2016 , and 2015 , and selected asset information as of December 31, 2017 and 2016 , regarding our operating segments are as follows (in thousands): Real Estate Segment Debt and Preferred Equity Segment Total Company Total revenues Years ended: December 31, 2017 $ 1,317,602 $ 193,871 $ 1,511,473 December 31, 2016 1,650,973 213,008 1,863,981 December 31, 2015 1,481,701 181,128 1,662,829 Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and gain (loss) on sale of marketable securities Years ended: December 31, 2017 $ 16,557 $ 170,363 $ 186,920 December 31, 2016 (197,000 ) 204,256 7,256 December 31, 2015 (71,634 ) 161,923 90,289 Total assets As of: December 31, 2017 $ 11,696,560 $ 2,286,344 $ 13,982,904 December 31, 2016 13,868,672 1,989,115 15,857,787 Income from continuing operations represents total revenues less total expenses for the real estate segment and total investment income less allocated interest expense for the debt and preferred equity segment. Interest costs for the debt and preferred equity segment includes actual costs incurred for investments collateralizing the MRA. Interest is imputed on the remaining investments using our corporate borrowing cost. We also allocate loan loss reserves, net of recoveries, and transaction related costs to the debt and preferred equity segment. We do not allocate marketing, general and administrative expenses to the debt and preferred equity segment since the use of personnel and resources is dependent on transaction volume between the two segments and varies period over period. In addition, we base performance on the individual segments prior to allocating marketing, general and administrative expenses. For the years ended, December 31, 2016, 2015, and 2014 marketing, general and administrative expenses totaled $100.5 million , $99.8 million , and $94.9 million respectively. All other expenses, except interest, relate entirely to the real estate assets. There were no transactions between the above two segments. The table below reconciles income from continuing operations to net income for the years ended December 31, 2017 , 2016 , and 2015 (in thousands): Year ended December 31, 2017 2016 2015 Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and gain (loss) on sale of marketable securities $ 186,920 $ 7,256 $ 90,289 Equity in net gain on sale of interest in unconsolidated joint venture/real estate 16,166 44,009 15,844 Purchase price fair value adjustment — — 40,078 Gain on sale of real estate, net 73,241 238,116 175,974 Depreciable real estate reserves (178,520 ) (10,387 ) (19,226 ) Loss on early extinguishment of debt — — (49 ) Gain (loss) on sale of investment in marketable securities 3,262 (83 ) — Income from continuing operations 101,069 278,911 302,910 Net income from discontinued operations — — 427 Gain on sale of discontinued operations — — 14,122 Net income $ 101,069 $ 278,911 $ 317,459

Quarterly Financial Data of the

Quarterly Financial Data of the Company (unaudited)	12 Months Ended
	Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Quarterly Financial Data of the Company/Operating Partnership (unaudited)	Quarterly Financial Data of the Company (unaudited) Summarized quarterly financial data for the years ended December 31, 2017 and 2016 was as follows (in thousands, except for per share amounts): 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 — $ 398,150 — $ 377,381 Income from continuing operations before equity in net income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain (loss) on sale of real estate, depreciable real estate reserves and gain on the sale of investment in marketable securities $ 47,234 $ 40,687 — $ 32,401 — $ 44,706 Equity in net income from unconsolidated joint ventures 7,788 4,078 — 3,412 — 6,614 Equity in net gain on sale of interest in unconsolidated joint venture/real estate — 1,030 — 13,089 — 2,047 Gain (loss) on sale of real estate, net 76,497 — — (3,823 ) — 567 Depreciable real estate reserves (93,184 ) — — (29,064 ) — (56,272 ) Gain on the sale of investment in marketable securities — — — — — 3,262 Noncontrolling interests and preferred unit distributions (6,616 ) (3,188 ) — (4,056 ) — 14,165 Net income attributable to SL Green 31,719 42,607 11,959 15,089 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) — (3,738 ) Net income attributable to SL Green common stockholders $ 27,982 $ 38,869 $ 8,222 $ 11,351 Net income attributable to common stockholders per common share—basic $ 0.29 $ 0.40 — $ 0.08 — $ 0.11 Net income attributable to common stockholders per common share—diluted $ 0.29 $ 0.40 — $ 0.08 — $ 0.11 2016 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 374,242 $ 416,681 $ 617,614 $ 455,444 Income (loss) from continuing operations before equity in net (loss) income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, depreciable real estate reserves and loss on sale of marketable securities $ 26,278 $ 46,689 $ (76,304 ) $ (1,281 ) Equity in net (loss) income from unconsolidated joint ventures (95 ) (3,968 ) 5,841 10,096 Equity in net gain on sale of interest in unconsolidated joint venture/real estate 421 225 33,448 9,915 Gain on sale of real estate, net 27,366 397 196,580 13,773 Depreciable real estate reserves — — (10,387 ) — Loss on the sale of investment in marketable securities — — (83 ) — Noncontrolling interests and preferred unit distributions (6,217 ) (5,353 ) (11,901 ) (5,544 ) Net income attributable to SL Green 47,753 37,990 137,194 26,959 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income attributable to SL Green common stockholders $ 44,016 $ 34,252 $ 133,457 $ 23,221 Net income attributable to common stockholders per common share—basic $ 0.44 $ 0.34 $ 1.33 $ 0.23 Net income attributable to common stockholders per common share—diluted $ 0.44 $ 0.34 $ 1.33 $ 0.23

Quarterly Financial Data of t35

Quarterly Financial Data of the Operating Partnership (unaudited)	12 Months Ended
	Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Quarterly Financial Data of the Company/Operating Partnership (unaudited)	Quarterly Financial Data of the Company (unaudited) Summarized quarterly financial data for the years ended December 31, 2017 and 2016 was as follows (in thousands, except for per share amounts): 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 — $ 398,150 — $ 377,381 Income from continuing operations before equity in net income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain (loss) on sale of real estate, depreciable real estate reserves and gain on the sale of investment in marketable securities $ 47,234 $ 40,687 — $ 32,401 — $ 44,706 Equity in net income from unconsolidated joint ventures 7,788 4,078 — 3,412 — 6,614 Equity in net gain on sale of interest in unconsolidated joint venture/real estate — 1,030 — 13,089 — 2,047 Gain (loss) on sale of real estate, net 76,497 — — (3,823 ) — 567 Depreciable real estate reserves (93,184 ) — — (29,064 ) — (56,272 ) Gain on the sale of investment in marketable securities — — — — — 3,262 Noncontrolling interests and preferred unit distributions (6,616 ) (3,188 ) — (4,056 ) — 14,165 Net income attributable to SL Green 31,719 42,607 11,959 15,089 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) — (3,738 ) Net income attributable to SL Green common stockholders $ 27,982 $ 38,869 $ 8,222 $ 11,351 Net income attributable to common stockholders per common share—basic $ 0.29 $ 0.40 — $ 0.08 — $ 0.11 Net income attributable to common stockholders per common share—diluted $ 0.29 $ 0.40 — $ 0.08 — $ 0.11 2016 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 374,242 $ 416,681 $ 617,614 $ 455,444 Income (loss) from continuing operations before equity in net (loss) income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, depreciable real estate reserves and loss on sale of marketable securities $ 26,278 $ 46,689 $ (76,304 ) $ (1,281 ) Equity in net (loss) income from unconsolidated joint ventures (95 ) (3,968 ) 5,841 10,096 Equity in net gain on sale of interest in unconsolidated joint venture/real estate 421 225 33,448 9,915 Gain on sale of real estate, net 27,366 397 196,580 13,773 Depreciable real estate reserves — — (10,387 ) — Loss on the sale of investment in marketable securities — — (83 ) — Noncontrolling interests and preferred unit distributions (6,217 ) (5,353 ) (11,901 ) (5,544 ) Net income attributable to SL Green 47,753 37,990 137,194 26,959 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income attributable to SL Green common stockholders $ 44,016 $ 34,252 $ 133,457 $ 23,221 Net income attributable to common stockholders per common share—basic $ 0.44 $ 0.34 $ 1.33 $ 0.23 Net income attributable to common stockholders per common share—diluted $ 0.44 $ 0.34 $ 1.33 $ 0.23
SL Green Operating Partnership
Condensed Income Statements, Captions [Line Items]
Quarterly Financial Data of the Company/Operating Partnership (unaudited)	Quarterly Financial Data of the Operating Partnership (unaudited) Summarized quarterly financial data for the years ended December 31, 2017 and 2016 was as follows (in thousands, except for per share amounts): 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 — $ 398,150 — $ 377,381 Income from continuing operations before equity in net income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain (loss) on sale of real estate, depreciable real estate reserves and gain on the sale of investment in marketable securities $ 47,234 $ 40,687 — $ 32,401 — $ 44,706 Equity in net income from unconsolidated joint ventures 7,788 4,078 — 3,412 — 6,614 Equity in net gain on sale of interest in unconsolidated joint venture/real estate — 1,030 — 13,089 — 2,047 Gain (loss) on sale of real estate, net 76,497 — — (3,823 ) — 567 Depreciable real estate reserves (93,184 ) — — (29,064 ) — (56,272 ) Gain on the sale of investment in marketable securities — — — — — 3,262 Noncontrolling interests and preferred unit distributions (5,328 ) (1,376 ) — (3,637 ) — 14,641 Net income attributable to SLGOP 33,007 44,419 — 12,378 15,565 Perpetual preferred units distributions (3,737 ) (3,738 ) — (3,737 ) — (3,738 ) Net income attributable to SLGOP common unitholders $ 29,270 $ 40,681 — $ 8,641 $ 11,827 Net income attributable to common unitholders per common unit—basic $ 0.29 $ 0.40 — $ 0.08 — $ 0.11 Net income attributable to common unitholders per common unit—diluted $ 0.29 $ 0.40 — $ 0.08 — $ 0.11 2016 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 374,242 $ 416,681 $ 617,614 $ 455,444 Income (loss) from continuing operations before equity in net (loss) income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, depreciable real estate reserves and loss on the sale of investment in marketable securities $ 26,278 $ 46,689 $ (76,304 ) $ (1,281 ) Equity in net (loss) income from unconsolidated joint ventures (95 ) (3,968 ) 5,841 10,096 Equity in net gain on sale of interest in unconsolidated joint venture/real estate 421 225 33,448 9,915 Gain on sale of real estate, net 27,366 397 196,580 13,773 Depreciable real estate reserves — — (10,387 ) — Loss on the sale of investment in marketable securities — — (83 ) — Noncontrolling interests and preferred unit distributions (4,252 ) (3,690 ) (6,315 ) (4,622 ) Net income attributable to SLGOP 49,718 39,653 142,780 27,881 Perpetual preferred units distributions (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income attributable to SLGOP common unitholders $ 45,981 $ 35,915 $ 139,043 $ 24,143 Net income attributable to common unitholders per common unit—basic $ 0.44 $ 0.34 $ 1.33 $ 0.23 Net income attributable to common unitholders per common unit—diluted $ 0.44 $ 0.34 $ 1.33 $ 0.23

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	Column A Column B Column C Column D Column E Description Balance at Beginning of Year Additions Charged Against Operations Uncollectible Accounts Written-off/Recovery (1) Balance at End of Year Year Ended December 31, 2017 Tenant and other receivables—allowance $ 16,592 $ 6,106 $ (4,061 ) $ 18,637 Deferred rent receivable—allowance $ 25,203 $ 2,321 $ (10,317 ) $ 17,207 Year Ended December 31, 2016 Tenant and other receivables—allowance $ 17,618 $ 10,630 $ (11,656 ) $ 16,592 Deferred rent receivable—allowance $ 21,730 $ 13,620 $ (10,147 ) $ 25,203 Year Ended December 31, 2015 Tenant receivables—allowance $ 18,068 $ 8,139 $ (8,589 ) $ 17,618 Deferred rent receivable—allowance $ 27,411 $ 2,789 $ (8,470 ) $ 21,730 (1) Includes the effect of properties that were sold and/or deconsolidated within the period.

Schedule III - Real Estate and

Schedule III - Real Estate and Accumulated Depreciation	12 Months Ended
	Dec. 31, 2017
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]
Schedule III - Real Estate and Accumulated Depreciation	Column A Column B Column C Initial Cost Column D Cost Capitalized Subsequent To Acquisition Column E Gross Amount at Which Carried at Close of Period Column F Column G Column H Column I Description Encumbrances Land Building & Improvements Land Building & Improvements Land Building & Improvements Total Accumulated Depreciation Date of Construction Date Acquired Life on Which Depreciation is Computed 420 Lexington Ave(1) $ 300,000 $ — $ 107,832 $ — $ 253,314 $ — $ 361,146 $ 361,146 $ 157,502 1927 3/1998 Various 711 Third Avenue(1)(2) — 19,844 42,499 — 66,553 19,844 109,052 128,896 39,396 1955 5/1998 Various 555 W. 57th Street(1) — 18,846 78,704 — 61,424 18,846 140,128 158,974 64,281 1971 1/1999 Various 220 East 42nd Street(1) 275,000 50,373 203,727 635 143,059 51,008 346,786 397,794 97,895 1929 2/2003 Various 461 Fifth Avenue(1) — — 62,695 — 16,185 — 78,880 78,880 28,378 1988 10/2003 Various 750 Third Avenue(1) — 51,093 205,972 — 42,543 51,093 248,515 299,608 93,469 1958 7/2004 Various 625 Madison Ave(1) — — 246,673 — 43,175 — 289,848 289,848 107,791 1956 10/2004 Various 485 Lexington Avenue(1) 450,000 77,517 326,825 765 110,648 78,282 437,473 515,755 168,921 1956 12/2004 Various 609 Fifth Avenue(1) — 36,677 145,954 — 10,435 36,677 156,389 193,066 46,059 1925 6/2006 Various 810 Seventh Avenue(1) — 114,077 476,386 — 71,735 114,077 548,121 662,198 162,606 1970 1/2007 Various 919 Third Avenue(1)(3) 500,000 223,529 1,033,198 35,410 68,413 258,939 1,101,611 1,360,550 303,424 1970 1/2007 Various 1185 Avenue of the Americas(1) — — 728,213 — 47,793 — 776,006 776,006 242,681 1969 1/2007 Various 1350 Avenue of the Americas(1) — 91,038 380,744 (97 ) 41,911 90,941 422,655 513,596 124,638 1966 1/2007 Various 100 Summit Lake Drive(4) — 10,526 43,109 — 11,215 10,526 54,324 64,850 16,963 1988 1/2007 Various 200 Summit Lake Drive(4) — 11,183 47,906 — 11,177 11,183 59,083 70,266 18,818 1990 1/2007 Various 500 Summit Lake Drive(4) — 9,777 39,048 — 6,358 9,777 45,406 55,183 13,074 1986 1/2007 Various 360 Hamilton Avenue(4) — 29,497 118,250 — 15,392 29,497 133,642 163,139 39,811 2000 1/2007 Various 1-6 Landmark Square(5) 100,000 50,947 195,167 — 51,515 50,947 246,682 297,629 70,120 1973-1984 1/2007 Various 7 Landmark Square(5) — 2,088 7,748 (367 ) 670 1,721 8,418 10,139 1,286 2007 1/2007 Various 1010 Washington Boulevard(5) — 7,747 30,423 — 7,378 7,747 37,801 45,548 11,044 1988 1/2007 Various 400 Summit Lake Drive(4) — 38,889 1 285 2 39,174 3 39,177 — --- 1/2007 N/A 1055 Washington Boulevard(5) — 13,516 53,228 — 8,390 13,516 61,618 75,134 18,075 1987 6/2007 Various 1 Madison Avenue(1) 486,153 172,641 654,394 905 15,801 173,546 670,195 843,741 175,971 1960 8/2007 Various 100 Church Street(1) 217,273 32,494 79,996 2,500 96,027 34,994 176,023 211,017 46,825 1959 1/2010 Various 125 Park Avenue(1) — 120,900 189,714 — 74,660 120,900 264,374 385,274 65,529 1923 10/2010 Various Williamsburg(6) — 3,677 14,708 2,523 (4,550 ) 6,200 10,158 16,358 1,865 2010 12/2010 Various 110 East 42nd Street(1) — 34,000 46,411 2,196 27,253 36,196 73,664 109,860 17,603 1921 5/2011 Various 400 East 58th Street(1)(7) 40,000 17,549 30,916 — 7,590 17,549 38,506 56,055 5,154 1929 1/2012 Various 752 Madison Avenue(1) — 282,415 7,131 1,871 58 284,286 7,189 291,475 1,180 1996/2012 1/2012 Various 762 Madison Avenue(1)(7) 771 6,153 10,461 — 131 6,153 10,592 16,745 1,627 1910 1/2012 Various 19-21 East 65th Street(1)(7) — — 7,389 — 364 — 7,753 7,753 1,141 1928-1940 1/2012 Various 304 Park Avenue(1) — 54,189 75,619 300 14,550 54,489 90,169 144,658 16,445 1930 6/2012 Various 635 Sixth Avenue(1) — 24,180 37,158 163 51,805 24,343 88,963 113,306 7,854 1902 9/2012 Various 641 Sixth Avenue(1) — 45,668 67,316 308 6,029 45,976 73,345 119,321 12,097 1902 9/2012 Various 1080 Amsterdam(1)(8) 36,363 — 27,445 — 20,489 — 47,934 47,934 4,216 1932 10/2012 Various Column A Column B Column C Initial Cost Column D Cost Capitalized Subsequent To Acquisition Column E Gross Amount at Which Carried at Close of Period Column F Column G Column H Column I Description Encumbrances Land Building & Improvements Land Building & Improvements Land Building & Improvements Total Accumulated Depreciation Date of Construction Date Acquired Life on Which Depreciation is Computed 315 West 33rd Street (1) 250,000 195,834 164,429 — 11,583 195,834 176,012 371,846 19,966 2000-2001 11/2013 Various 562 Fifth Avenue(1) — 57,052 10,487 — 1,213 57,052 11,700 68,752 3,596 1909/1920/1921 11/2013 Various 719 Seventh Avenue(1)(9) 41,622 41,850 — 2,336 34,055 44,186 34,055 78,241 215 1927 7/2014 Various 115 Spring Street(1) — 11,078 44,799 — 1,759 11,078 46,558 57,636 4,083 1900 7/2014 Various 635 Madison(1) — 205,632 15,805 — — 205,632 15,805 221,437 1,306 9/2014 N/A 1640 Flatbush Avenue(6) — 6,226 501 — 231 6,226 732 6,958 35 1966 3/2015 Various One Vanderbilt (1)(10) — 80,069 116,557 (80,069 ) (116,558 ) — (1 ) (1 ) — N/A 6/2001 - 11/2011 Various Upper East Side Residential (1)(11) — 48,152 — 13,323 — 61,475 — 61,475 — 1930 6/2015 Various 110 Greene Street (1)(7) — 45,120 215,470 — 9,611 45,120 225,081 270,201 15,693 1910 7/2015 Various 187 Broadway (1) — 7,600 9,412 (7,600 ) (154 ) — 9,258 9,258 9,258 1969 8/2015 Various 5-7 Dey Street (1) 58,000 13,400 34,175 13,050 10,481 26,450 44,656 71,106 34,136 1921 8/2015 Various 30 East 40th Street (1) — 4,650 20,000 2 4,197 4,652 24,197 28,849 534 1927 8/2015 Various 183 Broadway(1) — 5,799 23,431 (5,799 ) 923 — 24,354 24,354 24,354 1920 3/2016 Various Other(12) — 922 14,210 (3 ) 2 919 14,212 15,131 3,201 Various Total $ 2,755,182 $ 2,374,414 $ 6,492,236 $ (17,363 ) $ 1,356,835 $ 2,357,051 $ 7,849,071 $ 10,206,122 $ 2,300,116 (1) Property located in New York, New York. (2) We own a 50.0% interest in this property. (3) We own a 51.0% interest in this property. (4) Property located in Westchester County, New York. (5) Property located in Connecticut. (6) Property located in Brooklyn, New York. (7) We own a 90.0% interest in this property. (8) We own a 92.5% interest in this property. (9) We own a 75.0% interest in this property. (10) Properties at 317 Madison Avenue, 331 Madison Avenue and 51 East 42nd Street were demolished in preparation of the development site for the One Vanderbilt project. (11) We own a 95.1% interest in this property. (12) Other includes tenant improvements of eEmerge, capitalized interest and corporate improvements. The changes in real estate for the years ended December 31, 2017 , 2016 and 2015 are as follows (in thousands): 2017 2016 2015 Balance at beginning of year $ 12,743,332 $ 16,681,602 $ 14,069,141 Property acquisitions 13,323 29,230 3,064,137 Improvements 342,014 426,060 396,555 Retirements/disposals/deconsolidation (2,892,547 ) (4,393,560 ) (848,231 ) Balance at end of year $ 10,206,122 $ 12,743,332 $ 16,681,602 The aggregate cost of land, buildings and improvements, before depreciation, for Federal income tax purposes at December 31, 2017 was $9.2 billion (unaudited). The changes in accumulated depreciation, exclusive of amounts relating to equipment, autos, and furniture and fixtures, for the years ended December 31, 2017 , 2016 and 2015 are as follows (in thousands): 2017 2016 2015 Balance at beginning of year $ 2,264,694 $ 2,060,706 $ 1,905,165 Depreciation for year 347,015 353,502 480,523 Retirements/disposals/deconsolidation (311,593 ) (149,514 ) (324,982 ) Balance at end of year $ 2,300,116 $ 2,264,694 $ 2,060,706

Significant Accounting Polici38

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include our accounts and those of our subsidiaries, which are wholly-owned or controlled by us. Entities which we do not control through our voting interest and entities which are variable interest entities, but where we are not the primary beneficiary, are accounted for under the equity method. See Note 5, "Debt and Preferred Equity Investments" and Note 6, "Investments in Unconsolidated Joint Ventures." All significant intercompany balances and transactions have been eliminated. We consolidate a variable interest entity, or VIE, in which we are considered the primary beneficiary. The primary beneficiary is the entity that has (i) the power to direct the activities that most significantly impact the entity's economic performance and (ii) the obligation to absorb losses of the VIE or the right to receive benefits from the VIE that could be significant to the VIE. A noncontrolling interest in a consolidated subsidiary is defined as the portion of the equity (net assets) in a subsidiary not attributable, directly or indirectly, to us. Noncontrolling interests are required to be presented as a separate component of equity in the consolidated balance sheet and the presentation of net income is modified to present earnings and other comprehensive income attributed to controlling and noncontrolling interests. We assess the accounting treatment for each joint venture and debt and preferred equity investment. This assessment includes a review of each joint venture or limited liability company agreement to determine the rights provided to each party and whether those rights are protective or participating. For all VIEs, we review such agreements in order to determine which party has the power to direct the activities that most significantly impact the entity's economic performance. In situations where we and our partner approve, among other things, the annual budget, receive a detailed monthly reporting package, meet on a quarterly basis to review the results of the joint venture, review and approve the joint venture's tax return before filing, and approve all leases that cover more than a nominal amount of space relative to the total rentable space at each property, we do not consolidate the joint venture as we consider these to be substantive participation rights that result in shared power of the activities that most significantly impact the performance of the joint venture. Our joint venture agreements typically contain certain protective rights such as requiring partner approval to sell, finance or refinance the property and the payment of capital expenditures and operating expenditures outside of the approved budget or operating plan. In January 2018, the partnership agreement for our investment in the property at 919 Third Avenue was modified resulting in our partner now having substantive participating rights in the venture. As a result the investment will no longer be deemed a VIE and our investment in the property will be deconsolidated as of January 1, 2018. The Company will record its non-controlling interest at fair value. This fair value will be allocated to the assets and liabilities, including identified intangibles. Under this methodology, the leases are ascribed an in-place lease intangible value as well as an above or below market lease intangible value which will be amortized over the remaining term of the associated leases.
Investment in Commercial Real Estate Properties	Investment in Commercial Real Estate Properties Real estate properties are presented at cost less accumulated depreciation and amortization. Costs directly related to the development or redevelopment of properties are capitalized. Ordinary repairs and maintenance are expensed as incurred; major replacements and betterments, which improve or extend the life of the asset, are capitalized and depreciated over their estimated useful lives. We recognize the assets acquired, liabilities assumed (including contingencies) and any noncontrolling interests in an acquired entity at their respective fair values on the acquisition date. When we acquire our partner's equity interest in an existing unconsolidated joint venture and gain control over the investment, we record the consolidated investment at fair value. The difference between the book value of our equity investment on the purchase date and our share of the fair value of the investment's purchase price is recorded as a purchase price fair value adjustment in our consolidated statements of operations. See Note 3, "Property Acquisitions." We allocate the purchase price of real estate to land and building (inclusive of tenant improvements) and, if determined to be material, intangibles, such as the value of above- and below-market leases and origination costs associated with the in-place leases. We depreciate the amount allocated to building (inclusive of tenant improvements) over their estimated useful lives, which generally range from three to 40 years. We amortize the amount allocated to the above- and below-market leases over the remaining term of the associated lease, which generally range from one to 14 years, and record it as either an increase (in the case of below-market leases) or a decrease (in the case of above-market leases) to rental income. We amortize the amount allocated to the values associated with in-place leases over the expected term of the associated lease, which generally ranges from one to 14 years. If a tenant vacates its space prior to the contractual termination of the lease and no rental payments are being made on the lease, any unamortized balance of the related intangible will be written off. The tenant improvements and origination costs are amortized as an expense over the remaining life of the lease (or charged against earnings if the lease is terminated prior to its contractual expiration date). We assess fair value of the leases based on estimated cash flow projections that utilize appropriate discount and capitalization rates and available market information. Estimates of future cash flows are based on a number of factors including the historical operating results, known trends, and market/economic conditions that may affect the property. To the extent acquired leases contain fixed rate renewal options that are below-market and determined to be material, we amortize such below-market lease value into rental income over the renewal period. As of December 31, 2017 , the weighted average amortization period for above-market leases, below-market leases, and in-place lease costs is 6.0 years, 23.3 years, and 16.3 years, respectively. We incur a variety of costs in the development and leasing of our properties. After the determination is made to capitalize a cost, it is allocated to the specific component of a project that is benefited. Determination of when a development project is substantially complete and capitalization must cease involves a degree of judgment. The costs of land and building under development include specifically identifiable costs. The capitalized costs include, but are not limited to, pre-construction costs essential to the development of the property, development costs, construction costs, interest costs, real estate taxes, salaries and related costs and other costs incurred during the period of development. We consider a construction project as substantially completed and held available for occupancy upon the completion of tenant improvements, but no later than one year after major construction activity ceases. We cease capitalization on the portions substantially completed and occupied or held available for occupancy, and capitalize only those costs associated with the portions under construction. Properties are depreciated using the straight-line method over the estimated useful lives of the assets. The estimated useful lives are as follows: Category Term Building (fee ownership) 40 years Building improvements shorter of remaining life of the building or useful life Building (leasehold interest) lesser of 40 years or remaining term of the lease Property under capital lease remaining lease term Furniture and fixtures four to seven years Tenant improvements shorter of remaining term of the lease or useful life Depreciation expense (including amortization of capital lease assets) totaled $365.3 million , $783.5 million , and $523.8 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. On a periodic basis, we assess whether there are any indications that the value of our real estate properties may be other than temporarily impaired or that their carrying value may not be recoverable. A property's value is considered impaired if management's estimate of the aggregate future cash flows (undiscounted) to be generated by the property is less than the carrying value of the property. To the extent impairment has occurred, the loss will be measured as the excess of the carrying amount of the property over the calculated fair value of the property. We also evaluate our real estate properties for impairment when a property has been classified as held for sale. Real estate assets held for sale are valued at the lower of their carrying value or fair value less costs to sell and depreciation expense is no longer recorded. See Note 4, "Properties Held for Sale and Dispositions."
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid investments with maturity of three months or less when purchased to be cash equivalents.
Fair Value Measurements	We determine other than temporary impairment in real estate investments and debt and preferred equity investments, including intangibles primarily utilizing cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as sales comparison approach, which utilizes comparable sales, listings and sales contracts. All of which are classified as Level 3 inputs. As of December 31, 2017 , we held notes receivable totaling $250.0 million , which were purchased at par, and were in maturity default at the time of acquisition. In August 2017, the Company determined that it was probable that the loans would not be repaid in full and therefore, the loans were put on non-accrual status. The loans had an outstanding balance including accrued interest of $259.3 million at the time that they were put on non accrual status. The Company has initiated proceedings to foreclose on the property, and expects to take control of the property unless the buyer is able to repay the principal and interest, including default interest and fees, on the notes receivable in full prior to the completion of the foreclosure process. We believe the collateral value is sufficient to recover the carrying amounts of the notes receivable. The marketable securities classified as Level 1 were derived from quoted prices in active markets. The valuation technique used to measure the fair value of the marketable securities classified as Level 2 were valued based on quoted market prices or model driven valuations using the significant inputs derived from or corroborated by observable market data. Marketable securities in an unrealized loss position are not considered to be other than temporarily impaired. We do not intend to sell these securities and it is not more likely than not that we will be required to sell the investments before recovery of their amortized cost bases. The fair value of derivative instruments is based on current market data received from financial sources that trade such instruments and are based on prevailing market data and derived from third party proprietary models based on well-recognized financial principles and reasonable estimates about relevant future market conditions, which are classified as Level 2 inputs. The financial assets and liabilities that are not measured at fair value on our consolidated balance sheets include cash and cash equivalents, restricted cash, accounts receivable, accounts payable and accrued expenses, debt and preferred equity investments, mortgages and other loans payable and other secured and unsecured debt. The carrying amount of cash and cash equivalents, restricted cash, accounts receivable, and accounts payable and accrued expenses reported in our consolidated balance sheets approximates fair value due to the short term nature of these instruments. The fair value of debt and preferred equity investments, which is classified as Level 3, is estimated by discounting the future cash flows using current interest rates at which similar loans with the same maturities would be made to borrowers with similar credit ratings. The fair value of borrowings, which is classified as Level 3, is estimated by discounting the contractual cash flows of each debt instrument to their present value using adjusted market interest rates, which is provided by a third-party specialist. Fair Value Measurements We are required to disclose fair value information with regard to our financial instruments, whether or not recognized in the consolidated balance sheets, for which it is practical to estimate fair value. The FASB guidance defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. We measure and/or disclose the estimated fair value of financial assets and liabilities based on a hierarchy that distinguishes between market participant assumptions based on market data obtained from sources independent of the reporting entity and the reporting entity’s own assumptions about market participant assumptions. This hierarchy consists of three broad levels: Level 1 - quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the measurement date; Level 2 - inputs other than quoted prices included within Level 1, that are observable for the asset or liability, either directly or indirectly; and Level 3 - unobservable inputs for the asset or liability that are used when little or no market data is available. We follow this hierarchy for our assets and liabilities measured at fair value on a recurring and nonrecurring basis. In instances in which the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level of input that is significant to the fair value measurement in its entirety. Our assessment of the significance of the particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability.
Investment in Marketable Securities	Investment in Marketable Securities At acquisition, we designate a security as held-to-maturity, available-for-sale, or trading. As of December 31, 2017 , we did not have any securities designated as held-to-maturity or trading. We account for our available-for-sale securities at fair value pursuant to Accounting Standards Codification, or ASC, 820-10, with the net unrealized gains or losses reported as a component of accumulated other comprehensive income or loss. Any unrealized losses that are determined to be other-than-temporary are recognized in earnings up to their credit component. The cost of bonds and marketable securities sold is determined using the specific identification method.
Investments in Unconsolidated Joint Ventures	Investments in Unconsolidated Joint Ventures We account for our investments in unconsolidated joint ventures under the equity method of accounting in cases where we exercise significant influence over, but do not control, these entities and are not considered to be the primary beneficiary. We consolidate those joint ventures that we control or which are VIEs and where we are considered to be the primary beneficiary. In all these joint ventures, the rights of the joint venture partner are both protective as well as participating. Unless we are determined to be the primary beneficiary in a VIE, these participating rights preclude us from consolidating these VIE entities. These investments are recorded initially at cost, as investments in unconsolidated joint ventures, and subsequently adjusted for equity in net income (loss) and cash contributions and distributions. Equity in net income (loss) from unconsolidated joint ventures is allocated based on our ownership or economic interest in each joint venture. When a capital event (as defined in each joint venture agreement) such as a refinancing occurs, if return thresholds are met, future equity income will be allocated at our increased economic interest. We recognize incentive income from unconsolidated real estate joint ventures as income to the extent it is earned and not subject to a clawback feature. Distributions we receive from unconsolidated real estate joint ventures in excess of our basis in the investment are recorded as offsets to our investment balance if we remain liable for future obligations of the joint venture or may otherwise be committed to provide future additional financial support. None of the joint venture debt is recourse to us. The Company has performance guarantees under master leases at two joint ventures. See Note 6, "Investments in Unconsolidated Joint Ventures." We assess our investments in unconsolidated joint ventures for recoverability, and if it is determined that a loss in value of the investment is other than temporary, we write down the investment to its fair value. We evaluate our equity investments for impairment based on the joint ventures' projected discounted cash flows. We do not believe that the values of any of our equity investments were impaired at December 31, 2017 . We may originate loans for real estate acquisition, development and construction, where we expect to receive some of the residual profit from such projects. When the risk and rewards of these arrangements are essentially the same as an investor or joint venture partner, we account for these arrangements as real estate investments under the equity method of accounting for investments. Otherwise, we account for these arrangements consistent with the accounting for our debt and preferred equity investments.
Restricted Cash	Restricted Cash Restricted cash primarily consists of security deposits held on behalf of our tenants, interest reserves, as well as capital improvement and real estate tax escrows required under certain loan agreements.
Deferred Lease Costs	Deferred Lease Costs Deferred lease costs consist of fees and direct costs incurred to execute operating leases and are amortized on a straight-line basis over the related lease term. Certain of our employees provide leasing services to the wholly-owned properties.
Deferred Financing Costs	Deferred Financing Costs Deferred financing costs represent commitment fees, legal, title and other third party costs associated with obtaining commitments for financing which result in a closing of such financing. These costs are amortized over the terms of the respective agreements. Unamortized deferred financing costs are expensed when the associated debt is refinanced or repaid before maturity. Costs incurred in seeking financing transactions, which do not close, are expensed in the period in which it is determined that the financing will not close. Deferred debt issuance costs related to a recognized debt liability are presented in the balance sheet as a direct deduction from the carrying amount of that debt liability.
Revenue Recognition	We record a gain on sale of real estate when title is conveyed to the buyer, subject to the buyer's financial commitment being sufficient to provide economic substance to the sale and provided that we have no substantial economic involvement with the buyer. Interest income on debt and preferred equity investments is accrued based on the contractual terms of the instruments and when, in the opinion of management, it is deemed collectible. Some debt and preferred equity investments provide for accrual of interest at specified rates, which differ from current payment terms. Interest is recognized on such loans at the accrual rate subject to management's determination that accrued interest is ultimately collectible, based on the underlying collateral and operations of the borrower. If management cannot make this determination, interest income above the current pay rate is recognized only upon actual receipt. Deferred origination fees, original issue discounts and loan origination costs, if any, are recognized as an adjustment to interest income over the terms of the related investments using the effective interest method. Fees received in connection with loan commitments are also deferred until the loan is funded and are then recognized over the term of the loan as an adjustment to yield. Discounts or premiums associated with the purchase of loans are amortized or accreted into interest income as a yield adjustment on the effective interest method based on expected cash flows through the expected maturity date of the related investment. If we purchase a debt or preferred equity investment at a discount, intend to hold it until maturity and expect to recover the full value of the investment, we accrete the discount into income as an adjustment to yield over the term of the investment. If we purchase a debt or preferred equity investment at a discount with the intention of foreclosing on the collateral, we do not accrete the discount. For debt investments acquired at a discount for credit quality, the difference between contractual cash flows and expected cash flows at acquisition is not accreted. Anticipated exit fees, the collection of which is expected, are also recognized over the term of the loan as an adjustment to yield. Debt and preferred equity investments are placed on a non-accrual status at the earlier of the date at which payments become 90 days past due or when, in the opinion of management, a full recovery of interest income becomes doubtful. Interest income recognition on any non-accrual debt or preferred equity investment is resumed when such non-accrual debt or preferred equity investment becomes contractually current and performance is demonstrated to be resumed. Interest is recorded as income on impaired loans only to the extent cash is received. We may syndicate a portion of the loans that we originate or sell the loans individually. When a transaction meets the criteria for sale accounting, we derecognize the loan sold and recognize gain or loss based on the difference between the sales price and the carrying value of the loan sold. Any related unamortized deferred origination fees, original issue discounts, loan origination costs, discounts or premiums at the time of sale are recognized as an adjustment to the gain or loss on sale, which is included in investment income on the consolidated statement of operations. Any fees received at the time of sale or syndication are recognized as part of investment income. Asset management fees are recognized on a straight-line basis over the term of the asset management agreement. Revenue Recognition Rental revenue is recognized on a straight-line basis over the term of the lease. Rental revenue recognition commences when the tenant takes possession or controls the physical use of the leased space. In order for the tenant to take possession, the leased space must be substantially ready for its intended use. To determine whether the leased space is substantially ready for its intended use, management evaluates whether we are or the tenant is the owner of tenant improvements for accounting purposes. When management concludes that we are the owner of tenant improvements, rental revenue recognition begins when the tenant takes possession of the finished space, which is when such tenant improvements are substantially complete. In certain instances, when management concludes that we are not the owner (the tenant is the owner) of tenant improvements, rental revenue recognition begins when the tenant takes possession of or controls the space. When management concludes that we are the owner of tenant improvements for accounting purposes, we record amounts funded to construct the tenant improvements as a capital asset. For these tenant improvements, we record amounts reimbursed by tenants as a reduction of the capital asset. When management concludes that the tenant is the owner of tenant improvements for accounting purposes, we record our contribution towards those improvements as a lease incentive, which is included in deferred costs, net on our consolidated balance sheets and amortized as a reduction to rental revenue on a straight-line basis over the term of the lease. The excess of rents recognized over amounts contractually due pursuant to the underlying leases are included in deferred rents receivable on the consolidated balance sheets. We establish, on a current basis, an allowance for future potential tenant credit losses, which may occur against this account. The balance reflected on the consolidated balance sheets is net of such allowance. In addition to base rent, our tenants also generally will pay their pro rata share of increases in real estate taxes and operating expenses for the building over a base year. In some leases, in lieu of paying additional rent based upon increases in building operating expenses, the tenant will pay additional rent based upon increases in the wage rate paid to porters over the porters' wage rate in effect during a base year or increases in the consumer price index over the index value in effect during a base year. In addition, many of our leases contain fixed percentage increases over the base rent to cover escalations. Electricity is most often supplied by the landlord either on a sub-metered basis, or rent inclusion basis (i.e., a fixed fee is included in the rent for electricity, which amount may increase based upon increases in electricity rates or increases in electrical usage by the tenant). Base building services other than electricity (such as heat, air conditioning and freight elevator service during business hours, and base building cleaning) are typically provided at no additional cost, with the tenant paying additional rent only for services which exceed base building services or for services which are provided outside normal business hours. These escalations are based on actual expenses incurred in the prior calendar year. If the expenses in the current year are different from those in the prior year, then during the current year, the escalations will be adjusted to reflect the actual expenses for the current year.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts We maintain an allowance for doubtful accounts for estimated losses resulting from the inability of our tenants to make required payments. If the financial condition of a specific tenant were to deteriorate, resulting in an impairment of its ability to make payments, additional allowances may be required
Reserve for Possible Credit Losses	Reserve for Possible Credit Losses The expense for possible credit losses in connection with debt and preferred equity investments is the charge to earnings to increase the allowance for possible credit losses to the level that we estimate to be adequate, based on Level 3 data, considering delinquencies, loss experience and collateral quality. Other factors considered include geographic trends, product diversification, the size of the portfolio and current economic conditions. Based upon these factors, we establish a provision for possible credit loss on each individual investment. When it is probable that we will be unable to collect all amounts contractually due, the investment is considered impaired. Where impairment is indicated on an investment that is held to maturity, a valuation allowance is measured based upon the excess of the recorded investment amount over the fair value of the collateral. Any deficiency between the carrying amount of an asset and the calculated value of the collateral is charged to expense. We continue to assess or adjust our estimates based on circumstances of a loan and the underlying collateral. If additional information reflects increased recovery of our investment, we will adjust our reserves accordingly. There were no loan reserves recorded during the years ended December 31, 2017 , 2016 , and 2015 . Debt and preferred equity investments held for sale are carried at the lower of cost or fair market value using available market information obtained through consultation with dealers or other originators of such investments as well as discounted cash flow models based on Level 3 data pursuant to ASC 820-10. As circumstances change, management may conclude not to sell an investment designated as held for sale. In such situations, the investment will be reclassified at its net carrying value to debt and preferred equity investments held to maturity. For these reclassified investments, the difference between the current carrying value and the expected cash to be collected at maturity will be accreted into income over the remaining term of the investment
Rent Expense	Rent Expense Rent expense is recognized on a straight-line basis over the initial term of the lease. The excess of the rent expense recognized over the amounts contractually due pursuant to the underlying lease is included in the deferred lease payable on the consolidated balance sheets.
Underwriting Commissions and Costs	Underwriting Commissions and Costs Underwriting commissions and costs incurred in connection with our stock offerings are reflected as a reduction of additional paid-in-capital
Exchangeable Debt Instruments	Exchangeable Debt Instruments The initial proceeds from exchangeable debt that may be settled in cash, including partial cash settlements, are bifurcated between a liability component and an equity component associated with the embedded conversion option. The objective of the accounting guidance is to require the liability and equity components of exchangeable debt to be separately accounted for in a manner such that the interest expense on the exchangeable debt is not recorded at the stated rate of interest but rather at an effective rate that reflects the issuer's conventional debt borrowing rate at the date of issuance. We calculate the liability component of exchangeable debt based on the present value of the contractual cash flows discounted at our comparable market conventional debt borrowing rate at the date of issuance. The difference between the principal amount and the fair value of the liability component is reported as a discount on the exchangeable debt that is accreted as additional interest expense from the issuance date through the contractual maturity date using the effective interest method. A portion of this additional interest expense may be capitalized to the development and redevelopment balances qualifying for interest capitalization each period. The liability component of the exchangeable debt is reported net of discounts on our consolidated balance sheets. We calculate the equity component of exchangeable debt based on the difference between the initial proceeds received from the issuance of the exchangeable debt and the fair value of the liability component at the issuance date. The equity component is included in additional paid-in-capital, net of issuance costs, on our consolidated balance sheets. We allocate issuance costs for exchangeable debt between the liability and the equity components based on their relative values.
Transaction cost	Transaction Costs In January 2017, we adopted ASU No. 2017-01, Business Combinations: Clarifying the Definition of a Business, which changed how we account for transaction costs. Prior to January 2017, transaction costs were expensed as incurred. Starting in January 2017, transaction costs for asset acquisitions are capitalized to the investment basis which is then subject to a purchase price allocation based on relative fair value and transaction costs for business combinations or costs incurred on potential transactions which are not consummated are expensed as incurred.
Income Taxes	Income Taxes SL Green is taxed as a REIT under Section 856(c) of the Code. As a REIT, SL Green generally is not subject to Federal income tax. To maintain its qualification as a REIT, SL Green must distribute at least 90% of its REIT taxable income to its stockholders and meet certain other requirements. If SL Green fails to qualify as a REIT in any taxable year, SL Green will be subject to Federal income tax on its taxable income at regular corporate rates. SL Green may also be subject to certain state, local and franchise taxes. Under certain circumstances, Federal income and excise taxes may be due on its undistributed taxable income. The Operating Partnership is a partnership and, as a result, all income and losses of the partnership are allocated to the partners for inclusion in their respective income tax returns. The only provision for income taxes included in the consolidated statements of operations relates to the Operating Partnership’s consolidated taxable REIT subsidiaries. The Operating Partnership may also be subject to certain state, local and franchise taxes. Pursuant to amendments to the Code that became effective January 1, 2001, we have elected, and may elect in the future, to treat certain of our existing or newly created corporate subsidiaries as taxable REIT subsidiaries, or TRSs. In general, TRSs may perform non-customary services for the tenants of the Company, hold assets that we cannot hold directly and generally may engage in any real estate or non-real estate related business. The TRSs generate income, resulting in Federal and state income tax liability for these entities. During the years ended December 31, 2017 , 2016 and 2015 , we recorded Federal, state and local tax provisions of $4.3 million , $2.8 million , and $3.1 million , respectively. For the year ended December 31, 2017, the Company paid distributions on its common stock of $3.10 per share which represented $1.24 per share of ordinary income and $1.86 per share of capital gains. For the year ended December 31, 2016, the Company paid distributions on its common stock of $2.88 per share which represented $2.48 per share of ordinary income, and $0.40 per share of capital gains. For the year ended December 31, 2015, the Company paid distributions on its common stock of $2.40 per share which represented $0.00 per share of ordinary income and $2.40 per share of capital gains. We follow a two-step approach for evaluating uncertain tax positions. Recognition (step one) occurs when an enterprise concludes that a tax position, based solely on its technical merits, is more-likely-than-not to be sustained upon examination. Measurement (step two) determines the amount of benefit that is more-likely-than-not to be realized upon settlement. Derecognition of a tax position that was previously recognized would occur when a company subsequently determines that a tax position no longer meets the more-likely-than-not threshold of being sustained. The use of a valuation allowance as a substitute for derecognition of tax positions is prohibited. On December 22, 2017, the Tax Cuts
Stock-Based Employee Compensation Plans	Stock-Based Employee Compensation Plans We have a stock-based employee compensation plan, described more fully in Note 14, "Share-based Compensation." The Company's stock options are recorded at fair value at the time of issuance. Fair value of the stock options is determined using the Black-Scholes option pricing model. The Black-Scholes model was developed for use in estimating the fair value of traded options, which have no vesting restrictions and are fully transferable. In addition, option valuation models require the input of highly subjective assumptions including the expected stock price volatility. Because our plan has characteristics significantly different from those of traded options and because changes in the subjective input assumptions can materially affect the fair value estimate, in our opinion, the existing models do not necessarily provide a reliable single measure of the fair value of the employee stock options. Compensation cost for stock options, if any, is recognized over the vesting period of the award. Our policy is to grant options with an exercise price equal to the quoted closing market price of the Company's common stock on either the grant date or the date immediately preceding the grant date. Awards of stock or restricted stock are expensed as compensation over the benefit period based on the fair value of the stock on the grant date. For share-based awards with a performance or market measure, we recognize compensation cost over the requisite service period, using the accelerated attribution expense method. The requisite service period begins on the date the compensation committee of our board of directors authorizes the award, adopts any relevant performance measures and communicates the award to the employees. For programs with awards that vest based on the achievement of a performance condition or market condition, we determine whether it is probable that the performance condition will be met, and estimate compensation cost based on the fair value of the award at the applicable award date estimated using a binomial model or market quotes. For share-based awards for which there is no pre-established performance measure, we recognize compensation cost over the service vesting period, which represents the requisite service period, on a straight-line basis. In accordance with the provisions of our share-based incentive compensation plans, we accept the return of shares of the Company's common stock, at the current quoted market price, from certain key employees to satisfy minimum statutory tax-withholding requirements related to shares that vested during the period. Awards can also be made in the form of a separate series of units of limited partnership interest in the Operating Partnership called long-term incentive plan units, or LTIP units. LTIP units, which can be granted either as free-standing awards or in tandem with other awards under our stock incentive plan, are valued by reference to the value of the Company's common stock at the time of grant, and are subject to such conditions and restrictions as the compensation committee of the Company's board of directors may determine, including continued employment or service, computation of financial metrics and/or achievement of pre-established performance goals and objectives.
Derivative Instruments	Derivative Instruments In the normal course of business, we use a variety of commonly used derivative instruments, such as interest rate swaps, caps, collars and floors, to manage, or hedge, interest rate risk. Effectiveness is essential for those derivatives that we intend to qualify for hedge accounting. Some derivative instruments are associated with an anticipated transaction. In those cases, hedge effectiveness criteria also require that it be probable that the underlying transaction occurs. Instruments that meet these hedging criteria are formally designated as hedges at the inception of the derivative contract. To determine the fair values of derivative instruments, we use a variety of methods and assumptions that are based on market conditions and risks existing at each balance sheet date. For the majority of financial instruments including most derivatives, long-term investments and long-term debt, standard market conventions and techniques such as discounted cash flow analysis, option pricing models, replacement cost, and termination cost are used to determine fair value. All methods of assessing fair value result in a general approximation of value, and such value may never actually be realized. In the normal course of business, we are exposed to the effect of interest rate changes and limit these risks by following established risk management policies and procedures including the use of derivatives. To address exposure to interest rates, derivatives are used primarily to fix the rate on debt based on floating-rate indices and manage the cost of borrowing obligations. We use a variety of conventional derivative products. These derivatives typically include interest rate swaps, caps, collars and floors. We expressly prohibit the use of unconventional derivative instruments and using derivative instruments for trading or speculative purposes. Further, we have a policy of only entering into contracts with major financial institutions based upon their credit ratings and other factors. We may employ swaps, forwards or purchased options to hedge qualifying forecasted transactions. Gains and losses related to these transactions are deferred and recognized in net income as interest expense in the same period or periods that the underlying transaction occurs, expires or is otherwise terminated. Hedges that are reported at fair value and presented on the balance sheet could be characterized as cash flow hedges or fair value hedges. Interest rate caps and collars are examples of cash flow hedges. Cash flow hedges address the risk associated with future cash flows of interest payments. For all hedges held by us and which were deemed to be fully effective in meeting the hedging objectives established by our corporate policy governing interest rate risk management, no net gains or losses were reported in earnings. The changes in fair value of hedge instruments are reflected in accumulated other comprehensive income. For derivative instruments not designated as hedging instruments, the gain or loss, resulting from the change in the estimated fair value of the derivative instruments, is recognized in current earnings during the period of change.
Earnings per Share of the Company	Earnings per Share of the Company The Company presents both basic and diluted earnings per share, or EPS. Basic EPS excludes dilution and is computed by dividing net income or loss attributable to common stockholders by the weighted average number of common shares outstanding during the period. Basic EPS includes participating securities, consisting of unvested restricted stock that receive nonforfeitable dividends similar to shares of common stock. Diluted EPS reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock, where such exercise or conversion would result in a lower EPS amount. Diluted EPS also includes units of limited partnership interest. The dilutive effect of stock options is reflected in the weighted average diluted outstanding shares calculation by application of the treasury stock method. There is no dilutive effect for the exchangeable senior notes as the conversion premium will be paid in cash.
Earnings per Unit of the Operating Partnership	Earnings per Unit of the Operating Partnership The Operating Partnership presents both basic and diluted earnings per unit, or EPU. Basic EPU excludes dilution and is computed by dividing net income or loss attributable to common unitholders by the weighted average number of common units outstanding during the period. Basic EPU includes participating securities, consisting of unvested restricted units that receive nonforfeitable dividends similar to shares of common units. Diluted EPU reflects the potential dilution that could occur if securities or other contracts to issue common units were exercised or converted into common units, where such exercise or conversion would result in a lower EPU amount. The dilutive effect of unit options is reflected in the weighted average diluted outstanding units calculation by application of the treasury stock method. There is no dilutive effect for the exchangeable senior notes as the conversion premium will be paid in cash.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash investments, debt and preferred equity investments and accounts receivable. We place our cash investments with high quality financial institutions. The collateral securing our debt and preferred equity investments is located in the New York metropolitan area. See Note 5, "Debt and Preferred Equity Investments." We perform ongoing credit evaluations of our tenants and require most tenants to provide security deposits or letters of credit. Though these security deposits and letters of credit are insufficient to meet the total value of a tenant's lease obligation, they are a measure of good faith and a source of funds to offset the economic costs associated with lost revenue and the costs associated with re-tenanting a space. The properties in our real estate portfolio are located in the New York metropolitan area. The tenants located in our buildings operate in various industries.
Reclassification	Reclassification Certain prior year balances have been reclassified to conform to our current year presentation.
Accounting Standards Updates	Accounting Standards Updates In August 2017, the FASB issued Accounting Standards Update (ASU) No. 2017-12, Derivatives and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities. The amendments in the new standard will permit more flexibility in hedging interest rate risk for both variable rate and fixed rate financial instruments. The standard will also enhance the presentation of hedge results in the financial statements. The guidance is effective for fiscal years beginning after December 15, 2018 and early adoption is permitted. The Company has not yet adopted the guidance, and does not expect a material impact on the Company’s consolidated financial statements when the new standard is implemented. In May 2017, the FASB issued Accounting Standards Update (ASU) No. 2017-09, Compensation - Stock Compensation (Topic 718), Scope of Modification Accounting. The guidance clarifies the changes to the terms or conditions of a share-based payment award that require an entity to apply modification accounting in Topic 718. The guidance is effective for fiscal years beginning after December 15, 2017 and early adoption is permitted. The Company has not yet adopted the guidance, and does not expect a material impact on the Company’s consolidated financial statements when the new standard is implemented. In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business. The guidance clarifies the definition of a business and provides guidance to assist with determining whether transactions should be accounted for as acquisitions of assets or businesses. The main provision is that an acquiree is not a business if substantially all of the fair value of the gross assets is concentrated in a single identifiable asset or group of assets. The Company adopted the guidance on the issuance date effective January 5, 2017. The Company expects that most of its real estate acquisitions will be considered asset acquisitions under the new guidance and that transaction costs will be capitalized to the investment basis which is then subject to a purchase price allocation based on relative fair value. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. The guidance will require entities to show the changes on the total cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. As a result, entities will no longer present transfers between these items on the statement of cash flows. The guidance is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. The Company has not yet adopted this new guidance and is currently evaluating the impact of adopting this new accounting standard on the Company’s consolidated financial statements. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The ASU provides final guidance on eight cash flow issues, including debt prepayment or debt extinguishment costs, contingent consideration payments made after a business combination, distributions received from equity method investees, separately identifiable cash flows and application of the predominance principle, and others. The amendments in the ASU are effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The Company adopted the guidance effective January 1, 2017 and there was no impact on the Company’s consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The guidance changes how entities will measure credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. The guidance replaces the current ‘incurred loss’ model with an ‘expected loss’ approach. The guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted after December 2018. The Company has not yet adopted this new guidance and is currently evaluating the impact of adopting this new accounting standard on the Company’s consolidated financial statements. In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. The guidance simplifies the accounting for share-based payment award transactions including: income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. The guidance is effective for fiscal years beginning after December 15, 2016, including interim periods within those fiscal years. Early adoption is permitted. The Company adopted the guidance effective January 1, 2017 and there was no material impact on the Company’s consolidated financial statements. In March 2016, the FASB issued ASU 2016-07, Investments Equity Method and Joint Ventures (Topic 323). The guidance eliminates the requirement that an entity retroactively adopt the equity method of accounting if an investment qualifies for use of the equity method as a result of an increase in the level of ownership or degree of influence. The amendments require that the equity method investor add the cost of acquiring the additional interest in the investee to the current basis of the investor’s previously held interest and adopt the equity method of accounting as of the date the investment becomes qualified for equity method accounting. The Company adopted the guidance effective January 1, 2017 and there was no impact on the Company’s consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases. The guidance requires lessees to recognize lease assets and lease liabilities for those leases classified as operating leases under the previous standard. Depending on the lease classification, lessees will recognize expense based on the effective interest method for finance leases or on a straight-line basis for operating leases. The accounting applied by a lessor is largely unchanged from that applied under the previous standard. One of the potential impacts on the Company may be the presentation and disclosure in the financial statements of non-lease components such as charges to tenants for a building’s operating expenses. As currently written, the guidance would require that the non-lease components be presented separately from the lease components in both the Consolidated Statements of Operations and Consolidated Balance Sheets. In January 2018, the FASB issued an exposure draft, Leases (Topic 842) Targeted Improvements, which would provide lessors with a practical expedient to not separate non-lease components from the related lease component under certain conditions. We anticipate the majority of our leases would qualify for the practical expedient. We expect this guidance to be finalized in 2018 and, as a result, we would adopt the practical expedient. Another impact is the measurement and presentation of ground leases under which the Company is lessee. The Company is required to record a liability for the obligation to make payments under the lease and an asset for the right to use the underlying asset during the lease term and will also apply the new expense recognition requirements given the lease classification. The Company is currently quantifying these impacts. The guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. The Company expects to adopt this guidance January 1, 2019 and will apply the modified retrospective approach. In January 2016, the FASB issued ASU 2016-01 (Subtopic 825-10), Recognition and Measurement of Financial Assets and Financial Liabilities. The guidance requires entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value through earnings to record changes in instruments-specific credit risk for financial liabilities measured under the fair value option in other comprehensive income, use the exit price notion when measuring an instrument’s fair value for disclosure and to separately present financial assets and liabilities by measurement category and form of instrument on the balance sheet or in the notes to the financial statements. The guidance is effective for fiscal years beginning after December 15, 2017, and for interim periods therein. The Company has not yet adopted this new guidance and does not expect a material impact on the Company’s consolidated financial statements when the new standard is implemented. In May 2014, the FASB issued a new comprehensive revenue recognition guidance which requires us to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which we expect to be entitled in exchange for those goods and services (ASU 2014-09). The FASB also issued implementation guidance in March 2016, April 2016 and May 2016 - ASU’s 2016-08, 2016-10 and 2016-12, respectively. These ASUs are effective for annual and interim periods beginning after December 15, 2017. The Company will adopt this guidance January 1, 2018. Since the Company’s revenue is related to leasing activities, the adoption of this guidance will not have a material impact on the consolidated financial statements. The new guidance is applicable to service contracts with joint ventures for which the Company earns property management fees, leasing commissions and development and construction fees. The adoption of this new guidance does not change the accounting for these fees as the pattern of recognition of revenue does not change with the new guidance. We will continue to recognize revenue over time on these contracts because the customer simultaneously receives and consumes the benefits provided by our performance. Thus, the analysis of our contracts under the new revenue recognition standard is consistent with our current revenue recognition model. In February 2017, the FASB issued Accounting Standards Update (ASU) No. 2017-05 to clarify the scope of asset derecognition guidance in Subtopic 610-20, which also provided guidance on accounting for partial sales of nonfinancial assets. Subtopic 610-20 was issued in May 2014 as part of ASU 2014-09. The Company will adopt this guidance January 1, 2018, and apply the modified retrospective approach. Additionally, the Company will elect to adopt the practical expedient under ASC 606, Revenue from Contracts with Customers, which allows an entity to apply the guidance to only to contracts with non-customers that are open based on the ASU 360-20, Real Estate Sales, (i.e. failed sales) as of the adoption date. The Company had one open contract in 2017 with a non-customer that will be evaluated under ASC 610-20. The Company entered into an agreement to sell a portion of their interest in an entity that held a controlling interest in the property at 1515 Broadway. Upon execution of the agreement in 2017, the transaction was evaluated under ASC 360-20, Real Estate Sales, and did not meet the criteria for sale accounting. Upon adoption of ASC 606, this contract will have met the criteria for sale accounting under ASC 610-20 and will be recorded in the first quarter of 2018 as an adjustment to beginning retained earnings. Through the sale, the Company no longer retains a controlling interest, as defined in ASC 810, Consolidation, and the impact of this adjustment will be a gain of $0.6 billion from the sale of the partial interest and related step-up in basis to fair value of the non-controlling interest retained. The Company will use the purchase price paid by the third party as an indicator of fair value. This purchase price will be allocated to the assets and liabilities, including identified intangibles. Under this methodology the leases are ascribed an in-place lease intangible value as well as an above or below market lease intangible value which will be amortized over the remaining term of the associated leases.

Organization and Basis of Pre39

Organization and Basis of Presentation (Tables)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of interests in properties	As of December 31, 2017 , we owned the following interests in properties in the New York metropolitan area, primarily in midtown Manhattan. Our investments located outside of Manhattan are referred to as the Suburban properties: Consolidated Unconsolidated Total Location Property Type Number of Properties Approximate Square Feet (unaudited) Number of Properties Approximate Square Feet (unaudited) Number of Properties Approximate Square Feet (unaudited) Weighted Average Occupancy (1) (unaudited) Commercial: Manhattan Office 23 (2) 14,304,606 9 10,356,864 32 24,661,470 93.9 % Retail 4 (3) 302,583 9 347,970 13 650,553 94.5 % Development/Redevelopment 7 158,985 4 770,514 11 929,499 63.8 % Fee Interest 1 176,530 1 — 2 176,530 100.0 % 35 14,942,704 23 11,475,348 58 26,418,052 92.9 % Suburban Office 20 (4 ) 3,013,200 2 640,000 22 3,653,200 84.0 % Retail 1 52,000 — — 1 52,000 100.0 % Development/Redevelopment 1 1,000 1 — 2 1,000 100.0 % 22 3,066,200 3 640,000 25 3,706,200 84.3 % Total commercial properties 57 18,008,904 26 12,115,348 83 30,124,252 91.8 % Residential: Manhattan Residential 3 (3) 472,105 12 2,656,856 15 3,128,961 87.6 % Suburban Residential — — — — — — — % Total residential properties 3 472,105 12 2,656,856 15 3,128,961 87.6 % Total portfolio 60 18,481,009 38 14,772,204 98 33,253,213 91.4 % (1) The weighted average occupancy for commercial properties represents the total occupied square feet divided by total square footage at acquisition. The weighted average occupancy for residential properties represents the total occupied units divided by total available units. (2) Includes the property at 600 Lexington Avenue in New York, New York which is classified as held for sale at December 31, 2017. (3) As of December 31, 2017 , we owned a building that was comprised of approximately 270,132 square feet (unaudited) of retail space and approximately 222,855 square feet (unaudited) of residential space. For the purpose of this report, we have included the building in the number of retail properties we own. However, we have included only the retail square footage in the retail approximate square footage, and have listed the balance of the square footage as residential square footage. (4) Includes the properties at 115-117 Stevens Avenue in Valhalla, New York, and 1-6 International Drive in Rye Brook, New York which are classified as held for sale at December 31, 2017.

Significant Accounting Polici40

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of estimated useful lives	Properties are depreciated using the straight-line method over the estimated useful lives of the assets. The estimated useful lives are as follows: Category Term Building (fee ownership) 40 years Building improvements shorter of remaining life of the building or useful life Building (leasehold interest) lesser of 40 years or remaining term of the lease Property under capital lease remaining lease term Furniture and fixtures four to seven years Tenant improvements shorter of remaining term of the lease or useful life
Summary of identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases)	The following summarizes our identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases) as of December 31, 2017 and 2016 (in thousands): December 31, 2017 2016 Identified intangible assets (included in other assets): Gross amount $ 325,880 $ 651,099 Accumulated amortization (277,038 ) (410,930 ) Net (1) $ 48,842 $ 240,169 Identified intangible liabilities (included in deferred revenue): Gross amount $ 540,283 $ 655,930 Accumulated amortization (402,583 ) (464,749 ) Net (1) $ 137,700 $ 191,181 (1) As of December 31, 2017 , $13.9 million net intangible assets and $4.1 million net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale.
Schedule of estimated annual amortization of acquired above-market leases, net of acquired below-market leases	The estimated annual amortization of acquired above-market leases, net of acquired (below-market) leases (a component of rental revenue), for each of the five succeeding years is as follows (in thousands): 2018 $ (13,853 ) 2019 (13,250 ) 2020 (12,432 ) 2021 (3,950 ) 2022 (3,647 )
Schedule of estimated annual amortization of all other identifiable assets	The estimated annual amortization of all other identifiable assets (a component of depreciation and amortization expense) including tenant improvements for each of the five succeeding years is as follows (in thousands): 2018 $ 9,700 2019 7,716 2020 6,783 2021 3,927 2022 2,365
Schedule of marketable securities	At December 31, 2017 and 2016 , we held the following marketable securities (in thousands): December 31, 2017 2016 Equity marketable securities $ — $ 48,315 Commercial mortgage-backed securities 28,579 36,795 Total marketable securities available-for-sale $ 28,579 $ 85,110

Property Acquisitions (Tables)

Property Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property Acquisitions
Schedule of Fair Value of Equity Interest Immediately Before Acquisition Date	The acquisition-date fair value of the equity interest in 600 Lexington Avenue, which was acquired in 2015, immediately before the acquisition date and the resulting purchase price fair value adjustment, as determined in accordance with the methodology set out in the prior sentence, are as follows (in thousands): 600 Lexington Avenue Contract purchase price $ 284,000 Net consideration funded by us at closing, excluding consideration financed by debt (79,085 ) Debt assumed (112,795 ) Fair value of retained equity interest 92,120 Equity and/or debt investment held (54,575 ) Other (1) 2,533 Purchase price fair value adjustment $ 40,078 (1) Includes the acceleration of a deferred leasing commission from the joint venture to the Company.
Summary of Unaudited Pro Forma Basis Results of Operations	The following table summarizes, on an unaudited pro forma basis, the results of operations of 11 Madison Avenue, which are included in the consolidated results of operations for year ended December 31, 2015 as though the acquisition of 11 Madison Avenue was completed on January 1, 2015. The supplemental pro forma data is not necessarily indicative of what the actual results of operations would have been assuming the transactions had been completed as set forth above, nor do they purport to represent our results of operations for future periods. (in thousands, except per share/unit amounts) Actual revenues since acquisition $ 29,865 Actual net income since acquisition 159 Pro forma revenues 1,657,937 Pro forma income from continuing operations (1) 102,440 Pro forma basic earnings per share $ 0.76 Pro forma diluted earnings per share $ 0.75 Pro forma basic earnings per unit $ 0.76 Pro forma diluted earnings per unit $ 0.75 (1) The pro forma income from continuing operations for the year ended December 31, 2015 includes the effect of the incremental borrowings, including a $ 1.4 billion , 10 -year, interest only, fixed rate mortgage financing carrying a per annum stated interest rate of 3.838% to complete the acquisition and the preliminary allocation of purchase price.
2016 Acquisitions [Member]
Property Acquisitions
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	During the year ended December 31, 2017 , we did not acquire any properties from a third party. 2016 Acquisitions During the year ended December 31, 2016, the property listed below was acquired from a third party. The following summarizes our final allocation of the purchase price of the assets acquired and liabilities assumed upon the closing of this acquisition (in thousands): 183 Broadway Acquisition Date March 2016 Ownership Type Fee Interest Property Type Retail/Residential Purchase Price Allocation: Land $ 5,799 Building and building leasehold 23,431 Above-market lease value — Acquired in-place leases 773 Other assets, net of other liabilities 20 Assets acquired 30,023 Mark-to-market assumed debt — Below-market lease value (1,523 ) Derivatives — Liabilities assumed (1,523 ) Purchase price $ 28,500 Net consideration funded by us at closing, excluding consideration financed by debt $ 28,500 Equity and/or debt investment held $ — Debt assumed $ —
2015 Acquisitions
Property Acquisitions
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed		During the year ended December 31, 2016, we finalized the purchase price allocations for the following 2015 acquisitions based on facts and circumstances that existed at the acquisition date for each property (in thousands): 600 Lexington Avenue (1)(2) 187 Broadway and 5 & 7 Dey Street (1)(3) 11 Madison Avenue (1) 110 Greene Street (1)(4) Upper East Side Residential (1)(5) 1640 Flatbush Avenue (1) Acquisition Date December 2015 August 2015 August 2015 July 2015 June 2015 March 2015 Ownership Type Fee Interest Fee Interest Fee Interest Fee Interest Fee Interest Fee Interest Property Type Office Residential/Retail Office Office Residential/Retail Retail Purchase Price Allocation: Land $ 81,670 $ 20,266 $ 675,776 $ 45,120 $ 48,152 $ 6,226 Building and building leasehold 182,447 42,468 1,553,602 215,470 — 501 Above-market lease value 3,320 17 19,764 — — — Acquired in-place leases 22,449 3,621 366,949 8,967 1,922 146 Other assets, net of other liabilities — — — — — — Assets acquired 289,886 66,372 2,616,091 269,557 50,074 6,873 Mark-to-market assumed debt (55 ) — — — — — Below-market lease value (5,831 ) (3,226 ) (187,732 ) (14,557 ) — (73 ) Derivatives — — — — — — Liabilities assumed (5,886 ) (3,226 ) (187,732 ) (14,557 ) — (73 ) Purchase price $ 284,000 $ 63,146 $ 2,428,359 $ 255,000 $ 50,074 $ 6,800 Net consideration funded by us at closing, excluding consideration financed by debt $ 79,085 $ — $ — $ — $ — $ — Equity and/or debt investment held $ 54,575 $ — $ — $ — $ — $ — Debt assumed $ 112,795 $ — $ — $ — $ — $ — (1) Based on our preliminary analysis of the purchase price, we had allocated $97.0 million and $180.2 million to land and building, respectively, at 600 Lexington Avenue, $22.1 million and $41.0 million to land and building, respectively, at 187 Broadway and 5&7 Dey Street, $849.9 million and $1.6 billion to land and building, respectively, at 11 Madison Avenue, $89.3 million and $165.8 million to land and building, respectively, at 110 Greene Street, and $17.5 million and $32.5 million to land and building, respectively, at the Upper Eastside Residential Property and $6.1 million and $0.7 million to land and building, respectively, at 1640 Flatbush Avenue. The impact to our consolidated statements of operations for the twelve months ended December 31, 2015 was an increase in rental revenue of $7.8 million for the amortization of aggregate below-market leases and an additional $18.5 million of depreciation expense. (2) In December 2015, we acquired Canada Pension Plan Investment Board's 45% interest in this property, thereby consolidating full ownership of the property. The transaction valued the consolidated interests at $277.3 million . We recognized a purchase price fair value adjustment of $40.1 million upon closing of this transaction. This property, which we initially acquired in May 2010, was previously accounted for as an investment in unconsolidated joint ventures. (3) We acquired this property for consideration that included the issuance of $10.0 million and $26.9 million aggregate liquidation preferences of Series R and S Preferred Units, respectively, of limited partnership interest of the Operating Partnership and cash. (4) We acquired a 90.0% controlling interest in this property for consideration that included the issuance of $5.0 million and $6.7 million aggregate liquidation preferences of Series P and Q Preferred Units, respectively, of limited partnership interest of the Operating Partnership and cash. (5) We, along with our joint venture partner, acquired this property for consideration that included the issuance of $13.8 million aggregate liquidation preference of Series N Preferred Units of limited partnership interest of the Operating Partnership and cash. We hold a 95.1% controlling interest in this joint venture.
2014 Acquisitions
Property Acquisitions
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed

Properties Held for Sale and 42

Properties Held for Sale and Property Dispositions (Tables)	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Summary of properties sold and income from discontinued operations	The following table summarizes the properties sold during the years ended December 31, 2017 , 2016 , and 2015 : Property Disposition Date Property Type (unaudited) Approximate Usable Square Feet Sales Price (1) (in millions) Gain (Loss) on Sale (2) (in millions) 1515 Broadway (3) December 2017 Office 1,750,000 $ 1,950.0 $ — 125 Chubb Way (4) October 2017 Office 278,000 29.5 (26.1 ) 16 Court Street October 2017 Office 317,600 171.0 64.9 680-750 Washington Boulevard (5) July 2017 Office 325,000 97.0 (44.2 ) 520 White Plains Road (6) April 2017 Office 180,000 21.0 (14.6 ) 102 Greene Street (7) April 2017 Retail 9,200 43.5 4.9 400 East 57th Street October 2016 Residential 290,482 83.3 23.9 11 Madison Avenue (8) August 2016 Office 2,314,000 2,605.0 3.6 500 West Putnam (9) July 2016 Office 121,500 41.0 (10.4 ) 388 Greenwich June 2016 Office 2,635,000 2,002.3 206.5 7 International Drive May 2016 Land 31 Acres 20.0 (6.9 ) 248-252 Bedford Avenue February 2016 Residential 66,611 55.0 15.3 885 Third Avenue (10) February 2016 Land 607,000 453.0 (8.8 ) 140-150 Grand Street (11) December 2015 Office/Development 215,100 32.0 (20.1 ) 570 & 574 Fifth Avenue December 2015 Development 24,327 125.4 24.6 120 West 45th Street September 2015 Office 440,000 365.0 58.6 131-137 Spring Street (12) August 2015 Office 68,342 277.8 101.1 180 Maiden Lane January 2015 Office 1,090,000 470.0 17.0 (1) Sales price represents the actual sales price for an entire property or the gross asset valuation for interests in a property. (2) The gain on sale for 16 Court Street, 102 Greene Street, 400 East 57th Street, 11 Madison Avenue, 388 Greenwich, 248-252 Bedford Avenue, 570 & 574 Fifth Avenue, 120 West 45th Street, 131-137 Spring Street, and 180 Maiden Lane are net of $2.5 million , $0.9 million , $1.0 million , $0.6 million , $1.6 million , $1.3 million , $4.0 million , $2.0 million , $4.1 million , and $0.8 million in employee compensation accrued in connection with the realization of these investment gains. Additionally, amounts do not include adjustments for expenses recorded in subsequent periods. (3) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. See Note 6, "Investments in Unconsolidated Joint Ventures." (4) The Company recorded a $26.1 million charge in 2017 that is included in depreciable real estate reserves in the consolidated statement of operations. (5) The Company recorded a $44.2 million charge in 2017 that is included in depreciable real estate reserves in the consolidated statement of operations. (6) The Company recorded a $14.6 million charge in 2017 that is included in depreciable real estate reserves in the consolidated statement of operations. (7) In April 2017, we closed on the sale of a 90% interest 102 Greene Street and had subsequently accounted for our interest in the property as an investment in unconsolidated joint ventures. We sold the remaining 10% interest in September 2017. See Note 6, "Investments in Unconsolidated Joint Ventures." (8) In August 2016, we sold a 40% interest in 11 Madison Avenue. The sale did not meet the criteria for sale accounting and, as a result, the property was accounted for under the profit sharing method. In November 2016, the Company obtained consent to the modifications to the mortgage on the property, which resulted in the Company achieving sale accounting on the transaction. See Note 6, "Investments in Unconsolidated Joint Ventures." (9) The Company recorded a $10.4 million charge in 2016 that is included in depreciable real estate reserves in the consolidated statement of operations (10) In February 2016, we closed on the sale of 885 Third Avenue. The sale did not meet the criteria for sale accounting and as a result the property remained on our consolidated financial statements until the criteria was met in April 2017. (11) The Company recorded a $19.2 million charge in 2015 that is included in depreciable real estate reserves in the consolidated statement of operations. (12) We sold an 80% interest in 131-137 Spring Street and have subsequently accounted for our interest in the properties as an investment in unconsolidated joint ventures. See Note 6, "Investments in Unconsolidated Joint Ventures." The following table summarizes net income from discontinued operations for the years ended December 31, 2017 , 2016 , and 2015 respectively (in thousands): Year Ended December 31, 2017 2016 2015 Revenues Rental revenue $ — $ — $ 236 Escalation and reimbursement revenues — — (127 ) Other income — — — Total revenues — — 109 Operating expenses — — (631 ) Real estate taxes — — 250 Ground rent — — — Transaction related costs — — (49 ) Interest expense, net of interest income — — 109 Amortization of deferred financing costs — — 3 Depreciation and amortization — — — Total expenses — — (318 ) Net income from discontinued operations $ — $ — $ 427

Debt and Preferred Equity Inv43

Debt and Preferred Equity Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Schedule of debt and preferred equity book balance roll forward	Below is the rollforward analysis of the activity relating to our debt and preferred equity investments as of December 31, 2017 and 2016 (in thousands): December 31, 2017 December 31, 2016 Balance at beginning of period (1) $ 1,640,412 $ 1,670,020 Debt investment originations/accretion (2) 1,142,591 1,009,176 Preferred Equity investment originations/accretion (2) 144,456 5,698 Redemptions/sales/syndications/amortization (3) (813,418 ) (1,044,482 ) Balance at end of period (1) $ 2,114,041 $ 1,640,412 (1) Net of unamortized fees, discounts, and premiums. (2) Accretion includes amortization of fees and discounts and paid-in-kind investment income. (3) Certain participations in debt investments that were sold or syndicated did not meet the conditions for sale accounting are included in other assets and other liabilities on the consolidated balance sheets.
Summary of debt investments	As of December 31, 2017 and 2016 , we held the following debt investments with an aggregate weighted average current yield of 9.31% , excluding our investment in Two Herald Square, at December 31, 2017 (in thousands): Loan Type December 31, 2017 Future Funding Obligations December 31, 2017 Senior Financing December 31, 2017 Carrying Value (1) December 31, 2016 Carrying Value (1) Maturity Date (2) Fixed Rate Investments: Mortgage/Jr. Mortgage Loan (3) $ — $ — $ 250,464 $ — April 2017 Mortgage Loan (4) — — 26,366 26,311 February 2019 Mortgage Loan — — 239 380 August 2019 Mezzanine Loan (5a) — 1,160,000 204,005 — March 2020 Mezzanine Loan — 15,000 3,500 3,500 September 2021 Mezzanine Loan — 147,000 24,913 — April 2022 Mezzanine Loan — 86,976 12,699 12,692 November 2023 Mezzanine Loan (5b) — 115,000 12,932 12,925 June 2024 Mezzanine Loan — 95,000 30,000 30,000 January 2025 Mezzanine Loan — 340,000 15,000 15,000 November 2026 Mezzanine Loan — 1,657,500 55,250 — June 2027 Mezzanine Loan (6) — — — 66,129 Jr. Mortgage Participation/Mezzanine Loan (7) — — — 193,422 Total fixed rate $ — $ 3,616,476 $ 635,368 $ 360,359 Floating Rate Investments: Mezzanine Loan (5c)(8) $ 795 $ — $ 15,148 $ 15,051 March 2018 Mezzanine Loan — 40,000 19,982 19,913 April 2018 Jr. Mortgage Participation — 94,546 34,947 34,844 April 2018 Mezzanine Loan 523 20,523 10,934 10,863 August 2018 Mortgage/Mezzanine Loan — — 19,940 19,840 August 2018 Mortgage Loan — 65,000 14,955 14,880 August 2018 Mortgage/Mezzanine Loan (9) — — 16,969 16,960 September 2018 Mezzanine Loan — 37,500 14,855 14,648 September 2018 Mortgage/Mezzanine Loan (10) 391 — 23,609 20,423 October 2018 Mezzanine Loan 2,325 45,025 34,879 34,502 October 2018 Mezzanine Loan — 335,000 74,755 74,476 November 2018 Mezzanine Loan (5d)(8) — 85,000 15,381 15,141 December 2018 Mezzanine Loan (5e)(8) — 65,000 14,869 14,656 December 2018 Mezzanine Loan — 33,000 26,927 26,850 December 2018 Mezzanine Loan — 175,000 59,723 56,114 December 2018 Mezzanine Loan — 45,000 12,174 12,104 January 2019 Mortgage/Mezzanine Loan (5f) 26,284 — 162,553 — January 2019 Mezzanine Loan 5,372 25,289 8,550 5,410 January 2019 Mezzanine Loan — 38,000 21,939 21,891 March 2019 Mezzanine Loan 11 174,947 37,250 — April 2019 Mezzanine Loan — 265,000 24,830 24,707 April 2019 Mortgage/Jr. Mortgage Participation Loan 27,617 199,733 71,832 65,554 August 2019 Loan Type December 31, 2017 Future Funding Obligations December 31, 2017 Senior Financing December 31, 2017 Carrying Value (1) December 31, 2016 Carrying Value (1) Maturity Date (2) Mezzanine Loan 2,034 189,829 37,851 37,322 September 2019 Mortgage/Mezzanine Loan 36,391 — 143,919 111,819 September 2019 Mezzanine Loan — 350,000 34,737 — October 2019 Mortgage/Mezzanine Loan 25,643 — 43,845 33,682 January 2020 Mezzanine Loan (11) 3,621 555,379 75,834 125,911 January 2020 Mezzanine Loan 6,913 34,337 11,259 — July 2020 Mezzanine Loan (12) 51,494 310,654 75,428 63,137 November 2020 Mortgage and Mezzanine Loan 42,510 — 88,989 — December 2020 Mortgage and Mezzanine Loan — — 35,152 — December 2020 Jr. Mortgage Participation/Mezzanine Loan — 60,000 15,635 15,606 July 2021 Mezzanine Loan — 280,000 34,600 — August 2022 Mortgage/Mezzanine Loan (13) — — — 29,998 Mezzanine Loan (14) — — — 64,505 Mezzanine Loan (15) — — — 15,369 Mortgage/Mezzanine Loan (6) — — — 32,847 Mortgage/Mezzanine Loan (6) — — — 22,959 Mezzanine Loan (16) — — — 14,957 Mortgage/Mezzanine Loan (17) — — — 145,239 Total floating rate $ 231,924 $ 3,523,762 $ 1,334,250 $ 1,232,178 Total $ 231,924 $ 7,140,238 $ 1,969,618 $ 1,592,537 (1) Carrying value is net of discounts, premiums, original issue discounts and deferred origination fees. (2) Represents contractual maturity, excluding any unexercised extension options. (3) These loans were purchased at par in April and May 2017 and were in maturity default at the time of acquisition. At the time the loans were purchased, the Company expected to collect all contractually required payments, including interest. In August 2017, the Company determined that it was probable that the loans would not be repaid in full and therefore, the loans were put on non-accrual status. No impairment was recorded as the Company believes that the fair value of the property exceeds the carrying amount of the loans. The loans had an outstanding balance, including accrued interest, of $259.3 million at the time that they were put on non-accrual status. (4) In September 2014, we acquired a $26.4 million mortgage loan at a $0.2 million discount and a $5.7 million junior mortgage participation at a $5.7 million discount. The junior mortgage participation was a nonperforming loan at acquisition, is currently on non-accrual status and has no carrying value. (5) Carrying value is net of the following amounts that were sold or syndicated, which are included in other assets and other liabilities on the consolidated balance sheets as a result of the transfers not meeting the conditions for sale accounting: (a) $1.2 million , (b) $12.0 million , (c) $5.1 million (d) $14.6 million , (e) $14.1 million , and (f) $21.2 million . (6) This loan was repaid in June 2017. (7) This loan was repaid in March 2017. (8) This loan was extended in December 2017. (9) This loan was extended in August 2017. (10) This loan was extended in September 2017. (11) $66.1 million of outstanding principal was syndicated in February 2017. (12) This loan was extended in November 2017. (13) This loan was repaid in December 2017. (14) This loan was repaid in November 2017. (15) This loan was repaid in September 2017. (16) This loan was contributed to a joint venture in May 2017. (17) This loan was repaid in January 2017.
Summary of preferred equity investments	As of December 31, 2017 and 2016 , we held the following preferred equity investments with an aggregate weighted average current yield of 6.99% at December 31, 2017 (in thousands): Type December 31, 2017 Future Funding Obligations December 31, 2017 December 31, 2017 (1) December 31, 2016 (1) Mandatory Redemption (2) Preferred Equity (3) $ — $ 272,000 $ 144,423 $ — April 2021 Preferred Equity (4) — — — 9,982 Preferred Equity (5) — — — 37,893 $ — $ 272,000 $ 144,423 $ 47,875 (1) Carrying value is net of deferred origination fees. (2) Represents contractual maturity, excluding any unexercised extension options. (3) In February 2016, we closed on the sale of 885 Third Avenue and retained a preferred equity position in the property. The sale did not meet the criteria for sale accounting under the full accrual method in ASC 360-20, Property, Plant and Equipment - Real Estate Sales. As a result the property remained on our consolidated balance sheet until the criteria was met in April 2017 at which time the property was deconsolidated and the preferred equity investment was recognized. (4) This investment was redeemed in May 2017. (5) This investment was redeemed in April 2017.
Rollforward of total allowance for loan loss reserves	The following table is a rollforward of our total loan loss reserves at December 31, 2017 , 2016 and 2015 (in thousands): December 31, 2017 2016 2015 Balance at beginning of year $ — $ — $ — Expensed — — — Recoveries — — — Charge-offs and reclassifications — — — Balance at end of period $ — $ — $ —

Investments in Unconsolidated44

Investments in Unconsolidated Joint Ventures (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Schedule of general information on joint ventures	The table below provides general information on each of our joint ventures as of December 31, 2017 : Property Partner Ownership Interest (1) Economic Interest (1) Unaudited Approximate Square Feet Acquisition Date (2) Acquisition Price (2) (in thousands) 100 Park Avenue Prudential Real Estate Investors 49.90% 49.90% 834,000 February 2000 $ 95,800 717 Fifth Avenue Jeff Sutton/Private Investor 10.92% 10.92% 119,500 September 2006 251,900 800 Third Avenue Private Investors 60.52% 60.52% 526,000 December 2006 285,000 1745 Broadway Ivanhoe Cambridge, Inc. 56.87% 56.87% 674,000 April 2007 520,000 Jericho Plaza (3) Onyx Equities/Credit Suisse 11.67% 11.67% 640,000 April 2007 210,000 11 West 34th Street Private Investor/ Jeff Sutton 30.00% 30.00% 17,150 December 2010 10,800 3 Columbus Circle (4) The Moinian Group 48.90% 48.90% 741,500 January 2011 500,000 280 Park Avenue Vornado Realty Trust 50.00% 50.00% 1,219,158 March 2011 400,000 1552-1560 Broadway (5) Jeff Sutton 50.00% 50.00% 57,718 August 2011 136,550 724 Fifth Avenue Jeff Sutton 50.00% 50.00% 65,010 January 2012 223,000 10 East 53rd Street Canadian Pension Plan Investment Board 55.00% 55.00% 354,300 February 2012 252,500 521 Fifth Avenue Plaza Global Real Estate Partners LP 50.50% 50.50% 460,000 November 2012 315,000 21 East 66th Street (6) Private Investors 32.28% 32.28% 13,069 December 2012 75,000 650 Fifth Avenue (7) Jeff Sutton 50.00% 50.00% 69,214 November 2013 — 121 Greene Street Jeff Sutton 50.00% 50.00% 7,131 September 2014 27,400 175-225 Third Street Brooklyn, New York KCLW 3rd Street LLC/LIVWRK LLC 95.00% 95.00% — October 2014 74,600 55 West 46th Street Prudential Real Estate Investors 25.00% 25.00% 347,000 November 2014 295,000 Stonehenge Portfolio (8) Various Various Various 1,439,016 February 2015 36,668 131-137 Spring Street Invesco Real Estate 20.00% 20.00% 68,342 August 2015 277,750 605 West 42nd Street The Moinian Group 20.00% 20.00% 927,358 April 2016 759,000 11 Madison Avenue PGIM Real Estate 60.00% 60.00% 2,314,000 August 2016 2,605,000 333 East 22nd Street (9) Private Investors 33.33% 33.33% 26,926 August 2016 — 400 E 57th Street (10) BlackRock, Inc and Stonehenge Partners 51.00% 41.00% 290,482 October 2016 170,000 One Vanderbilt (11) National Pension Service of Korea/Hines Interest LP 71.01% 71.01% — January 2017 3,310,000 Mezzanine Loan (12) Private Investors 33.33% 33.33% — May 2017 15,000 Worldwide Plaza (13) RXR Realty / New York REIT / Private Investor 24.35% 24.35% 2,048,725 October 2017 1,725,000 1515 Broadway (14) Allianz Real Estate of America 69.87% 69.87% 1,750,000 November 2017 1,950,000 (1) Ownership interest and economic interest represent the Company's interests in the joint venture as of December 31, 2017 . Changes in ownership or economic interests within the current year are disclosed in the notes below. (2) Acquisition date and price represent the date on which the Company initially acquired an interest in the joint venture and the actual or implied gross purchase price for the joint venture on that date. Acquisition date and price are not adjusted for subsequent acquisitions or dispositions of interest. (3) During the fourth quarter of 2017, the Company recorded a $6.6 million charge in connection with this investment. This charge is included in depreciable real estate reserves in the consolidated statement of operations. (4) As a result of the sale of a condominium interest in September 2012, Young & Rubicam, Inc., or Y&R, owns floors three through eight at the property. Because the joint venture has an option to repurchase these floors, the gain associated with this sale was deferred. (5) The purchase price represents only the purchase of the 1552 Broadway interest which comprised approximately 13,045 square feet. The joint venture also owns a long-term leasehold interest in the retail space and certain other spaces at 1560 Broadway, which is adjacent to 1552 Broadway. (6) We hold a 32.28% interest in three retail and two residential units at the property and a 16.14% interest in three residential units at the property. (7) The joint venture owns a long-term leasehold interest in the retail space at 650 Fifth Avenue. In connection with the ground lease obligation, SLG provided a performance guaranty and our joint venture partner executed a contribution agreement to reflect its pro rata obligation. In the event the property is converted into a condominium unit and the landlord elects the purchase option, the joint venture shall be obligated to acquire the unit at the then fair value. (8) In March 2017, the Company sold a partial interest in the Stonehenge Portfolio as further described under Sale of Joint Venture Interest of Properties below. In February 2018, the Company, together with its joint venture partner, closed on the sale of one property from the Stonehenge Portfolio. (9) The joint venture acquired a leasehold interest in the property in October 2016. (10) In October 2016, the Company sold a 49% interest in this property to an investment account managed BlackRock, Inc. The Company's interest in the property was sold within a consolidated joint venture owned 90% by the Company and 10% by Stonehenge. The transaction resulted in the deconsolidation of the venture's remaining 51% interest in the property. The Company's joint venture with Stonehenge remains consolidated resulting in the combined 51% interest being shown within investments in unconsolidated joint ventures on the Company's balance sheet. (11) In January 2017, the Company admitted two partners, National Pension Service of Korea and Hines Interest LP, into the One Vanderbilt development project. In April 2017, the criteria for deconsolidation were met, and the development is shown within investments in unconsolidated joint ventures. The partners have committed aggregate equity to the project totaling no less than $525 million and their ownership interest in the joint venture is based on their capital contributions, up to an aggregate maximum of 29.0% . At December 31, 2017 the total of the two partners' ownership interests based on equity contributed was 3.48% . (12) In May 2017, the Company contributed a mezzanine loan secured by a commercial property in midtown Manhattan to a joint venture and retained a 33.33% interest in the venture. The carrying value is net of $10.0 million that was sold, which is included in other assets and other liabilities on the consolidated balance sheets as a result of the transfers not meeting the conditions for sale accounting. The loan matures in November 2018. (13) In September 2017, the Company and RXR Realty formed a joint venture in which each partner owns a 50% interest. In October 2017, this joint venture purchased a 48.7% interest in the property known as Worldwide Plaza from New York REIT. New York REIT owns the remaining 51.3% with its existing partner. (14) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method at December 31, 2017. Under the profit sharing method the Company recognized its share of the operations of the property and also recognized the other partner's share of depreciation. Included in equity in net income from unconsolidated joint ventures is $0.9 million of depreciation for the year ended December 31, 2017 representing the other partner's share of depreciation. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. As of December 31, 2017 and 2016 , the carrying value for acquisition, development and construction arrangements were as follows (in thousands): Loan Type December 31, 2017 December 31, 2016 Maturity Date Mezzanine Loan and Preferred Equity $ 100,000 $ 100,000 March 2018 Mezzanine Loan (1) 44,823 45,622 February 2022 Mezzanine Loan (2) 26,716 24,542 July 2036 $ 171,539 $ 170,164 (1) We have an option to convert our loan to an equity interest subject to certain conditions. We have determined that our option to convert the loan to equity is not a derivative financial instrument pursuant to GAAP. (2) The Company has the ability to convert this loan into an equity position starting in 2021 and the borrower is able to force this conversion in 2024. The combined balance sheets for the unconsolidated joint ventures, at December 31, 2017 and 2016 , are as follows (in thousands): December 31, 2017 December 31, 2016 Assets Commercial real estate property, net $ 12,822,133 $ 9,131,717 Cash and restricted cash 494,909 328,455 Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance 349,944 232,778 Debt and preferred equity investments, net 202,539 336,164 Other assets 1,407,806 683,481 Total assets $ 15,277,331 $ 10,712,595 Liabilities and members' equity Mortgages and other loans payable, net $ 9,412,101 $ 6,453,966 Deferred revenue/gain 985,648 356,414 Other liabilities 411,053 391,500 Members' equity 4,468,529 3,510,715 Total liabilities and members' equity $ 15,277,331 $ 10,712,595 Company's investments in unconsolidated joint ventures $ 2,362,989 $ 1,890,186 The combined statements of operations for the unconsolidated joint ventures, from acquisition date through the years ended December 31, 2017 , 2016 , and 2015 are as follows (in thousands): Year Ended December 31, 2017 2016 2015 Total revenues $ 904,230 $ 712,689 $ 576,845 Operating expenses 157,610 126,913 106,613 Ground rent 16,794 14,924 14,083 Real estate taxes 142,774 111,673 89,734 Interest expense, net of interest income 250,063 197,741 199,126 Amortization of deferred financing costs 23,026 24,829 13,394 Transaction related costs 146 5,566 615 Depreciation and amortization 279,419 199,011 149,023 Total expenses $ 869,832 $ 680,657 $ 572,588 Loss on early extinguishment of debt (7,899 ) (1,606 ) (1,089 ) Net income before gain on sale $ 26,499 $ 30,426 $ 3,168 Company's equity in net income from unconsolidated joint ventures $ 21,892 $ 11,874 $ 13,028 The first mortgage notes and other loans payable collateralized by the respective joint venture properties and assignment of leases at December 31, 2017 and 2016 , respectively, are as follows (amounts in thousands): Property Economic Interest (1) Maturity Date Interest Rate (2) December 31, 2017 December 31, 2016 Fixed Rate Debt: 521 Fifth Avenue 50.50 % November 2019 3.73% $ 170,000 $ 170,000 717 Fifth Avenue (3) 10.92 % July 2022 4.45% 300,000 300,000 717 Fifth Avenue (3) 10.92 % July 2022 5.50% 355,328 355,328 650 Fifth Avenue (4) 50.00 % October 2022 4.46% 210,000 — 650 Fifth Avenue (4) 50.00 % October 2022 5.45% 65,000 — 21 East 66th Street 32.28 % April 2023 3.60% 12,000 12,000 3 Columbus Circle 48.90 % March 2025 3.61% 350,000 350,000 1515 Broadway 69.87 % March 2025 3.93% 872,528 — 11 Madison Avenue 60.00 % September 2025 3.84% 1,400,000 1,400,000 800 Third Avenue 60.52 % February 2026 3.37% 177,000 177,000 400 East 57th Street 41.00 % November 2026 3.00% 100,000 100,000 Worldwide Plaza 24.35 % November 2027 3.98% 1,200,000 — Stonehenge Portfolio (5) Various Various 4.17% 357,282 362,518 1745 Broadway (6) — 340,000 Total fixed rate debt $ 5,569,138 $ 3,566,846 Floating Rate Debt: Jericho Plaza (7) 11.67 % March 2018 L+ 4.15% $ 81,099 $ 76,993 724 Fifth Avenue 50.00 % April 2018 L+ 2.42% 275,000 275,000 175-225 Third Street Brooklyn, New York 95.00 % June 2018 Prime+ 1.00% 40,000 40,000 280 Park Avenue 50.00 % September 2019 L+ 1.73% 1,200,000 900,000 121 Greene Street 50.00 % November 2019 L+ 1.50% 15,000 15,000 1745 Broadway (8) 56.87 % January 2020 L+ 1.85% 345,000 — 10 East 53rd Street 55.00 % February 2020 L+ 2.25% 170,000 125,000 131-137 Spring Street 20.00 % August 2020 L+ 1.55% 141,000 141,000 1552 Broadway 50.00 % October 2020 L+ 2.65% 195,000 185,410 55 West 46th Street (9) 25.00 % November 2020 L+ 2.13% 171,444 157,322 11 West 34th Street 30.00 % January 2021 L+ 1.45% 23,000 23,000 100 Park Avenue 49.90 % February 2021 L+ 1.75% 360,000 360,000 One Vanderbilt (10) 71.01 % September 2021 L+ 3.50% 355,535 — Property Economic Interest (1) Maturity Date Interest Rate (2) December 31, 2017 December 31, 2016 605 West 42nd Street 20.00 % August 2027 L+ 1.44% 550,000 539,000 21 East 66th Street 32.28 % June 2033 1 Year Treasury+ 2.75% 1,648 1,726 Stonehenge Portfolio Various April 2018 L+ 1.25% 55,340 65,577 650 Fifth Avenue (11) — 77,500 Total floating rate debt $ 3,979,066 $ 2,982,528 Total joint venture mortgages and other loans payable $ 9,548,204 $ 6,549,374 Deferred financing costs, net (136,103 ) (95,408 ) Total joint venture mortgages and other loans payable, net $ 9,412,101 $ 6,453,966 (1) Economic interest represents the Company's interests in the joint venture as of December 31, 2017 . Changes in ownership or economic interests, if any, within the current year are disclosed in the notes to the investment in unconsolidated joint ventures note above. (2) Interest rate as of December 31, 2017 , taking into account interest rate hedges in effect during the period. Floating rate debt is presented with the stated interest rate spread over 30-day LIBOR, unless otherwise specified. (3) These loans are comprised of a $300.0 million fixed rate mortgage loan and $355.3 million mezzanine loan. The mezzanine loan is subject to accretion based on the difference between contractual interest rate and contractual pay rate. (4) In November 2017, we closed on a $65.0 million mezzanine loan with a fixed interest rate of 545 basis points and a maturity date of October 2022. As a result, the $225.0 million mortgage loan was reduced to $210.0 million with a fixed interest rate of 446 basis points. These loans are now comprised of a $210.0 million fixed rate mortgage loan and $65.0 million fixed rate mezzanine loan. (5) Amount is comprised of $33.8 million , $137.1 million , $171.6 million , and $14.8 million in fixed-rate mortgages that mature in January 2018, August 2019, June 2024, and February 2027, respectively. In January 2018, the fixed-rate mortgage set to mature in January 2018 was refinanced with a $38.0 million mortgage loan with a floating interest rate of 140 basis points over 30-day LIBOR and a maturity date of January 2021. (6) In January 2017, this loan was refinanced with a floating rate loan as shown above. (7) The property secures a two year $100.0 million loan, of which $81.1 million is currently outstanding. (8) This loan has a committed amount of $375.0 million , of which $30.0 million was unfunded as of December 31, 2017 . (9) This loan has a committed amount of $195.0 million , of which $23.6 million was unfunded as of December 31, 2017 . (10) This loan is a $1.5 billion construction facility in connection with the development of One Vanderbilt. This facility bears interest at 350 basis points over 30-day LIBOR, with reductions based on meeting certain conditions, and has an initial five -year term with two one -year extension options. Advances under the loan are subject to incurred costs, funded equity, loan to value thresholds, and entering into construction contracts. (11) In September 2017, this loan was refinanced with a fixed rate loan as shown above.
Discontinued Operations, Disposed of by Sale
Schedule of Equity Method Investments [Line Items]
Schedule of general information on joint ventures	The following table summarizes the investments in unconsolidated joint ventures sold during the years ended December 31, 2017 , 2016 , and 2015 : Property Ownership Interest Disposition Date Type of Sale Gross Asset Valuation (in thousands) (1) Gain (Loss) on Sale (in thousands) (2) 102 Greene Street 10.00% September 2017 Ownership Interest $ 43,500 $ 283 Stonehenge Portfolio (partial) Various March 2017 Ownership Interest 300,000 871 EOP Denver 0.48% September 2016 Ownership Interest 180,700 300 33 Beekman (3) 45.90% May 2016 Property 196,000 33,000 EOP Denver 4.79% March 2016 Ownership Interest 180,700 2,800 7 Renaissance Square 50.00% March 2016 Property 20,700 4,200 1 Jericho Plaza (4) 66.11% February 2016 Ownership Interest 95,200 3,300 The Meadows 50.00% August 2015 Property 121,100 (1,600 ) 315 West 36th Street 35.50% September 2015 Ownership Interest 115,000 16,300 (1) Represents implied gross valuation for the joint venture or sales price of the property. (2) Represents the Company's share of the gain or loss. The gain on sale is net of $0 , $1.1 million , and $1.2 million of employee compensation accrued in connection with the realization of these investment gains in the years ended December 31, 2017 , 2016 , and 2015 , respectively. Additionally, amounts do not include adjustments for expenses recorded in subsequent periods. (3) In connection with the sale of the property, we also recognized a promote of $10.8 million . (4) Our ownership percentage was reduced in the first quarter of 2016, from 77.78% to 11.67% , upon completion of a restructuring of the joint venture.

Deferred Costs (Tables)

Deferred Costs (Tables)	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Deferred Costs	Deferred costs at December 31, 2017 and 2016 consisted of the following (in thousands): December 31, 2017 2016 Deferred leasing costs $ 443,341 $ 468,971 Less: accumulated amortization (217,140 ) (201,371 ) Deferred costs, net $ 226,201 $ 267,600

Mortgages and Other Loans Pay46

Mortgages and Other Loans Payable (Tables)	12 Months Ended
	Dec. 31, 2017
Mortgages and Other Loans Payable
Schedule of senior unsecured notes and other related disclosures by scheduled maturity date	The first mortgages and other loans payable collateralized by the respective properties and assignment of leases or debt investments at December 31, 2017 and 2016 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) December 31, 2017 December 31, 2016 Fixed Rate Debt: Unsecured Loan June 2018 4.81% $ 16,000 $ 16,000 One Madison Avenue May 2020 5.91% 486,153 517,806 762 Madison Avenue February 2022 5.00% 771 7,694 100 Church Street July 2022 4.68% 217,273 221,446 919 Third Avenue (2) June 2023 5.12% 500,000 500,000 420 Lexington Avenue October 2024 3.99% 300,000 300,000 400 East 58th Street (3) November 2026 3.00% 40,000 40,000 Landmark Square January 2027 4.90% 100,000 100,000 485 Lexington Avenue February 2027 4.25% 450,000 450,000 1080 Amsterdam (4) February 2027 3.58% 36,363 — 315 West 33rd Street February 2027 4.17% 250,000 — Series J Preferred Units (5) April 2051 3.75% 4,000 4,000 1515 Broadway (6) — 888,531 885 Third Avenue (7) — 267,650 FHLBNY Facility (8) — 105,000 FHLBNY Facility (8) — 100,000 Total fixed rate debt $ 2,400,560 $ 3,518,127 Floating Rate Debt: 719 Seventh Avenue (9) February 2018 L+ 3.05% $ 41,622 $ 37,388 183, 187 Broadway & 5-7 Dey Street May 2018 L+ 2.70% 58,000 58,000 2017 Master Repurchase Agreement June 2018 L+ 2.38% 90,809 — 220 East 42nd Street October 2020 L+ 1.60% 275,000 275,000 2016 Master Repurchase Agreement (10) — 184,642 One Vanderbilt Avenue (11) — 64,030 1080 Amsterdam (12) — 3,525 Total floating rate debt $ 465,431 $ 622,585 Total fixed rate and floating rate debt $ 2,865,991 $ 4,140,712 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 2,865,991 $ 4,140,712 Deferred financing costs, net of amortization (28,709 ) (66,882 ) Total mortgages and other loans payable, net $ 2,837,282 $ 4,073,830 (1) Interest rate as of December 31, 2017 , taking into account interest rate hedges in effect during the period. Floating rate debt is presented with the stated interest rate spread over 30-day LIBOR, unless otherwise specified. (2) We own a 51.0% controlling interest in the consolidated joint venture that is the borrower on this loan. In January 2018, the partnership agreement for our investment in the property at 919 Third Avenue was modified resulting in our partner now having substantive participating rights in the venture. As a result the investment will no longer be deemed a VIE and our investment in the property will be deconsolidated as of January 1, 2018. (3) The loan carries a fixed interest rate of 300 basis points for the first five years and is prepayable without penalty at the end of year five . (4) The loan is comprised of a $35.5 million mortgage loan and $0.9 million subordinate loan with a fixed interest rate of 350 basis points and 700 basis points, respectively, for the first five years and is prepayable without penalty at the end of year five . (5) In connection with the acquisition of a commercial real estate property, the Operating Partnership issued $4.0 million , 3.75% Series J Preferred Units of limited partnership interest, or the Series J Preferred Units, with a mandatory liquidation preference of $1,000 per unit. The Series J Preferred Units are accounted for as debt because they can be redeemed in cash by the Operating Partnership on the earlier of (i) the date of the sale of the property or (ii) April 30, 2051 or at the option of the unitholders as provided for in the related agreement. (6) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. This property is presented as an unconsolidated joint venture as of December 31, 2017 . The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. (7) In February 2016, we closed on the sale of 885 Third Avenue. The sale did not meet the criteria for sale accounting at that time. In April 2017, the mortgage was refinanced by the buyer, resulting in the Company deconsolidating the property from its financial statements in the second quarter of 2017. (8) The facility was repaid in January 2017. (9) In January 2018, we exercised an one year extension option to extend the maturity date to February 2019. (10) The master repurchase agreement was repaid in October 2017. (11) In September 2016, we closed on a $1.5 billion construction facility in connection with the development of One Vanderbilt Avenue. In January 2017, we admitted two partners, National Pension Service of Korea and Hines Interest LP, into the One Vanderbilt Avenue development project. In April 2017, the criteria for deconsolidation were met, and the development is shown within investments in unconsolidated joint ventures. See Note 6, "Investments in Unconsolidated Joint Ventures". (12) The following table sets forth our senior unsecured notes and other related disclosures as of December 31, 2017 and 2016 , respectively, by scheduled maturity date (dollars in thousands): Issuance December 31, 2017 Unpaid Principal Balance December 31, 2017 Accreted Balance December 31, 2016 Accreted Balance Coupon Rate (1) Initial Term (in Years) Maturity Date August 5, 2011 (2) $ 250,000 $ 249,953 $ 249,880 5.00 % 7 August 2018 March 16, 2010 (2) 250,000 250,000 250,000 7.75 % 10 March 2020 October 5, 2017 (3) 500,000 499,489 — 3.25 % 5 October 2022 November 15, 2012 (4) 300,000 305,163 200,000 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 October 12, 2010 (5) — — 334,077 $ 1,400,000 $ 1,404,605 $ 1,133,957 Deferred financing costs, net (8,666 ) (5,642 ) $ 1,400,000 $ 1,395,939 $ 1,128,315 (1) Interest on the senior unsecured notes is payable semi-annually with principal and unpaid interest due on the scheduled maturity dates. (2) Issued by the Company, the Operating Partnership and ROP, as co-obligors. (3) Issued by the Operating Partnership with the Company and ROP as guarantors. (4) In October 2017, the Company, the Operating Partnership and ROP, as co-obligors, issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022. The notes were priced at 105.334% . (5) In accordance with the terms of the indenture, the notes became exchangeable commencing September 14, 2017 and the Operating Partnership elected to settle exchanges in cash. In October 2017, all note holders elected to exchange the notes and the notes were repaid for $350.8 million , excluding accrued interest based on the applicable exchange rate.

Corporate Indebtedness (Tables)

Corporate Indebtedness (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of senior unsecured notes and other related disclosures by scheduled maturity date	The first mortgages and other loans payable collateralized by the respective properties and assignment of leases or debt investments at December 31, 2017 and 2016 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) December 31, 2017 December 31, 2016 Fixed Rate Debt: Unsecured Loan June 2018 4.81% $ 16,000 $ 16,000 One Madison Avenue May 2020 5.91% 486,153 517,806 762 Madison Avenue February 2022 5.00% 771 7,694 100 Church Street July 2022 4.68% 217,273 221,446 919 Third Avenue (2) June 2023 5.12% 500,000 500,000 420 Lexington Avenue October 2024 3.99% 300,000 300,000 400 East 58th Street (3) November 2026 3.00% 40,000 40,000 Landmark Square January 2027 4.90% 100,000 100,000 485 Lexington Avenue February 2027 4.25% 450,000 450,000 1080 Amsterdam (4) February 2027 3.58% 36,363 — 315 West 33rd Street February 2027 4.17% 250,000 — Series J Preferred Units (5) April 2051 3.75% 4,000 4,000 1515 Broadway (6) — 888,531 885 Third Avenue (7) — 267,650 FHLBNY Facility (8) — 105,000 FHLBNY Facility (8) — 100,000 Total fixed rate debt $ 2,400,560 $ 3,518,127 Floating Rate Debt: 719 Seventh Avenue (9) February 2018 L+ 3.05% $ 41,622 $ 37,388 183, 187 Broadway & 5-7 Dey Street May 2018 L+ 2.70% 58,000 58,000 2017 Master Repurchase Agreement June 2018 L+ 2.38% 90,809 — 220 East 42nd Street October 2020 L+ 1.60% 275,000 275,000 2016 Master Repurchase Agreement (10) — 184,642 One Vanderbilt Avenue (11) — 64,030 1080 Amsterdam (12) — 3,525 Total floating rate debt $ 465,431 $ 622,585 Total fixed rate and floating rate debt $ 2,865,991 $ 4,140,712 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 2,865,991 $ 4,140,712 Deferred financing costs, net of amortization (28,709 ) (66,882 ) Total mortgages and other loans payable, net $ 2,837,282 $ 4,073,830 (1) Interest rate as of December 31, 2017 , taking into account interest rate hedges in effect during the period. Floating rate debt is presented with the stated interest rate spread over 30-day LIBOR, unless otherwise specified. (2) We own a 51.0% controlling interest in the consolidated joint venture that is the borrower on this loan. In January 2018, the partnership agreement for our investment in the property at 919 Third Avenue was modified resulting in our partner now having substantive participating rights in the venture. As a result the investment will no longer be deemed a VIE and our investment in the property will be deconsolidated as of January 1, 2018. (3) The loan carries a fixed interest rate of 300 basis points for the first five years and is prepayable without penalty at the end of year five . (4) The loan is comprised of a $35.5 million mortgage loan and $0.9 million subordinate loan with a fixed interest rate of 350 basis points and 700 basis points, respectively, for the first five years and is prepayable without penalty at the end of year five . (5) In connection with the acquisition of a commercial real estate property, the Operating Partnership issued $4.0 million , 3.75% Series J Preferred Units of limited partnership interest, or the Series J Preferred Units, with a mandatory liquidation preference of $1,000 per unit. The Series J Preferred Units are accounted for as debt because they can be redeemed in cash by the Operating Partnership on the earlier of (i) the date of the sale of the property or (ii) April 30, 2051 or at the option of the unitholders as provided for in the related agreement. (6) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. This property is presented as an unconsolidated joint venture as of December 31, 2017 . The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. (7) In February 2016, we closed on the sale of 885 Third Avenue. The sale did not meet the criteria for sale accounting at that time. In April 2017, the mortgage was refinanced by the buyer, resulting in the Company deconsolidating the property from its financial statements in the second quarter of 2017. (8) The facility was repaid in January 2017. (9) In January 2018, we exercised an one year extension option to extend the maturity date to February 2019. (10) The master repurchase agreement was repaid in October 2017. (11) In September 2016, we closed on a $1.5 billion construction facility in connection with the development of One Vanderbilt Avenue. In January 2017, we admitted two partners, National Pension Service of Korea and Hines Interest LP, into the One Vanderbilt Avenue development project. In April 2017, the criteria for deconsolidation were met, and the development is shown within investments in unconsolidated joint ventures. See Note 6, "Investments in Unconsolidated Joint Ventures". (12) The following table sets forth our senior unsecured notes and other related disclosures as of December 31, 2017 and 2016 , respectively, by scheduled maturity date (dollars in thousands): Issuance December 31, 2017 Unpaid Principal Balance December 31, 2017 Accreted Balance December 31, 2016 Accreted Balance Coupon Rate (1) Initial Term (in Years) Maturity Date August 5, 2011 (2) $ 250,000 $ 249,953 $ 249,880 5.00 % 7 August 2018 March 16, 2010 (2) 250,000 250,000 250,000 7.75 % 10 March 2020 October 5, 2017 (3) 500,000 499,489 — 3.25 % 5 October 2022 November 15, 2012 (4) 300,000 305,163 200,000 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 October 12, 2010 (5) — — 334,077 $ 1,400,000 $ 1,404,605 $ 1,133,957 Deferred financing costs, net (8,666 ) (5,642 ) $ 1,400,000 $ 1,395,939 $ 1,128,315 (1) Interest on the senior unsecured notes is payable semi-annually with principal and unpaid interest due on the scheduled maturity dates. (2) Issued by the Company, the Operating Partnership and ROP, as co-obligors. (3) Issued by the Operating Partnership with the Company and ROP as guarantors. (4) In October 2017, the Company, the Operating Partnership and ROP, as co-obligors, issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022. The notes were priced at 105.334% . (5) In accordance with the terms of the indenture, the notes became exchangeable commencing September 14, 2017 and the Operating Partnership elected to settle exchanges in cash. In October 2017, all note holders elected to exchange the notes and the notes were repaid for $350.8 million , excluding accrued interest based on the applicable exchange rate.
Schedule of combined aggregate principal maturities	Combined aggregate principal maturities of mortgages and other loans payable, 2017 credit facility, trust preferred securities, senior unsecured notes and our share of joint venture debt as of December 31, 2017 , including as-of-right extension options and put options, were as follows (in thousands): Scheduled Amortization Principal Revolving Credit Facility Unsecured Term Loans Trust Preferred Securities Senior Unsecured Notes Total Joint Venture Debt 2018 $ 37,971 $ 206,431 $ — $ — $ — $ 250,000 $ 494,402 $ 200,250 2019 42,289 — — — — — 42,289 717,682 2020 23,487 679,531 — — — 250,000 953,018 473,809 2021 11,656 — — — — — 11,656 449,740 2022 9,448 198,555 — — — 800,000 1,008,003 223,330 Thereafter 16,675 1,639,948 40,000 1,500,000 100,000 100,000 3,396,623 2,119,481 $ 141,526 $ 2,724,465 $ 40,000 $ 1,500,000 $ 100,000 $ 1,400,000 $ 5,905,991 $ 4,184,292
Schedule of consolidated interest expense, excluding capitalized interest	Consolidated interest expense, excluding capitalized interest, was comprised of the following (in thousands): Year Ended December 31, 2017 2016 2015 Interest expense before capitalized interest $ 284,649 $ 348,062 $ 357,926 Interest capitalized (26,020 ) (24,067 ) (31,108 ) Interest income (1,584 ) (2,796 ) (2,948 ) Interest expense, net $ 257,045 $ 321,199 $ 323,870

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Schedule of amounts due from/to related parties	Amounts due from joint ventures and related parties at December 31, 2017 and 2016 consisted of the following (in thousands): December 31, 2017 2016 Due from joint ventures $ 15,025 $ 1,240 Other 8,014 14,616 Related party receivables $ 23,039 $ 15,856

Noncontrolling Interests on t49

Noncontrolling Interests on the Company's Consolidated Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Schedule of Noncontrolling Interest	Below is the rollforward analysis of the activity relating to the noncontrolling interests in the Operating Partnership as of December 31, 2017 and 2016 (in thousands): December 31, 2017 2016 Balance at beginning of period $ 473,882 $ 424,206 Distributions (14,266 ) (12,671 ) Issuance of common units 25,723 78,495 Redemption of common units (21,574 ) (31,805 ) Net income 3,995 10,136 Accumulated other comprehensive income allocation (94 ) 1,299 Fair value adjustment (5,712 ) 4,222 Balance at end of period $ 461,954 $ 473,882
Schedule of Preferred Unit Activity	Below is the rollforward analysis of the activity relating to the preferred units in the Operating Partnership as of December 31, 2017 and 2016 (in thousands): December 31, 2017 2016 Balance at beginning of period $ 302,010 $ 282,516 Issuance of preferred units — 22,793 Redemption of preferred units (275 ) (3,299 ) Balance at end of period $ 301,735 $ 302,010

Stockholders' Equity of the C50

Stockholders' Equity of the Company (Tables)	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Class of Treasury Stock	At December 31, 2017 repurchases under the plan were as follows: Period Number of shares purchased Average price paid per share Cumulative number of shares purchased as part of the repurchase plan or programs Maximum approximate dollar value of shares that may yet be purchased under the plan (in millions) (1) First quarter 2017 63,812 $103.84 63,812 $1,493.4 Second quarter 2017 2,384,323 $103.40 2,448,135 $1,246.8 Third quarter 2017 951,866 $101.67 3,400,001 $1,150.0 Fourth quarter 2017 (2) 4,942,410 $100.76 8,342,411 $652.0 (1) Reflective of $1.5 billion plan maximum as of December 31, 2017 . (2) Includes 413,700 shares of common stock repurchased by the Company in December 2017 that were settled in January 2018.
Schedule of Common Stock Issued and Proceeds Received Dividend Reinvestments	The following table summarizes SL Green common stock issued, and proceeds received from dividend reinvestments and/or stock purchases under the DRSPP for the year ended December 31, 2017 , 2016 , and 2015 , respectively (in thousands): Year Ended December 31, 2017 2016 2015 Common Stock Shares Issued 2,141 2,687 775,760 Dividend reinvestments/stock purchases under the DRSPP $ 223 $ 277 $ 99,555
Schedule of Earnings Per Share	SL Green's earnings per share for the years ended December 31, 2017 , 2016 , and 2015 are computed as follows (in thousands): Year Ended December 31, Numerator 2017 2016 2015 Basic Earnings: Income attributable to SL Green common stockholders $ 86,424 $ 234,946 $ 269,132 Effect of Dilutive Securities: Redemption of units to common shares 3,995 10,136 10,565 Diluted Earnings: Income attributable to SL Green common stockholders $ 90,419 $ 245,082 $ 279,697 Year Ended December 31, Denominator 2017 2016 2015 Basic Shares: Weighted average common stock outstanding 98,571 100,185 99,345 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,556 4,323 3,899 Stock-based compensation plans 276 373 490 Diluted weighted average common stock outstanding 103,403 104,881 103,734 The Operating Partnership's earnings per unit for the years ended December 31, 2017 , 2016 , and 2015 respectively are computed as follows (in thousands): Year Ended December 31, Numerator 2017 2016 2015 Basic and Diluted Earnings: Income attributable to SLGOP common unitholders $ 90,419 $ 245,082 $ 279,697 Year Ended December 31, Denominator 2017 2016 2015 Basic units: Weighted average common units outstanding 103,127 104,508 103,244 Effect of Dilutive Securities: Stock-based compensation plans 276 373 490 Diluted weighted average common units outstanding 103,403 104,881 103,734

Partners' Capital of the Oper51

Partners' Capital of the Operating Partnership (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Earnings Per Share	SL Green's earnings per share for the years ended December 31, 2017 , 2016 , and 2015 are computed as follows (in thousands): Year Ended December 31, Numerator 2017 2016 2015 Basic Earnings: Income attributable to SL Green common stockholders $ 86,424 $ 234,946 $ 269,132 Effect of Dilutive Securities: Redemption of units to common shares 3,995 10,136 10,565 Diluted Earnings: Income attributable to SL Green common stockholders $ 90,419 $ 245,082 $ 279,697 Year Ended December 31, Denominator 2017 2016 2015 Basic Shares: Weighted average common stock outstanding 98,571 100,185 99,345 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,556 4,323 3,899 Stock-based compensation plans 276 373 490 Diluted weighted average common stock outstanding 103,403 104,881 103,734 The Operating Partnership's earnings per unit for the years ended December 31, 2017 , 2016 , and 2015 respectively are computed as follows (in thousands): Year Ended December 31, Numerator 2017 2016 2015 Basic and Diluted Earnings: Income attributable to SLGOP common unitholders $ 90,419 $ 245,082 $ 279,697 Year Ended December 31, Denominator 2017 2016 2015 Basic units: Weighted average common units outstanding 103,127 104,508 103,244 Effect of Dilutive Securities: Stock-based compensation plans 276 373 490 Diluted weighted average common units outstanding 103,403 104,881 103,734

Share-based Compensation (Table

Share-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of weighted average assumptions used to estimate the grant date fair value of options granted	The fair value of each stock option or LTIP Unit granted is estimated on the date of grant using the Black-Scholes option pricing model based on historical information with the following weighted average assumptions for grants during the years ended December 31, 2017 , 2016 , and 2015 . 2017 2016 2015 Dividend yield 2.51 % 2.37 % 1.97 % Expected life 4.4 years 3.7 years 3.6 years Risk-free interest rate 1.73 % 1.57 % 1.43 % Expected stock price volatility 28.10 % 26.76 % 32.34 %
Summary of the status of stock options and changes during the period	A summary of the status of the Company's stock options as of December 31, 2017 , 2016 , and 2015 and changes during the years ended December 31, 2017 , 2016 , and 2015 are as follows: 2017 2016 2015 Options Outstanding Weighted Average Exercise Price Options Outstanding Weighted Average Exercise Price Options Weighted Balance at beginning of year $ 1,737,213 $ 98.44 $ 1,595,007 $ 95.52 $ 1,462,726 $ 87.98 Granted 174,000 105.66 445,100 105.86 389,836 112.54 Exercised (292,193 ) 81.07 (192,875 ) 76.90 (217,438 ) 74.69 Lapsed or canceled (70,301 ) 121.68 (110,019 ) 123.86 (40,117 ) 98.61 Balance at end of year $ 1,548,719 $ 101.48 $ 1,737,213 $ 98.44 $ 1,595,007 $ 95.52 Options exercisable at end of year 800,902 $ 94.33 748,617 $ 87.72 589,055 $ 89.85 Weighted average fair value of options granted during the year $ 3,816,652 $ 8,363,036 $ 9,522,613
Schedule of other share-based compensation, activity	A summary of the Company's restricted stock as of December 31, 2017 , 2016 , and 2015 and charges during the years ended December 31, 2017 , 2016 , and 2015 are as follows: 2017 2016 2015 Balance at beginning of year 3,202,031 3,137,881 3,000,979 Granted 96,185 98,800 143,053 Canceled — (34,650 ) (6,151 ) Balance at end of year 3,298,216 3,202,031 3,137,881 Vested during the year 95,736 83,822 87,081 Compensation expense recorded $ 9,809,749 $ 7,153,966 $ 7,540,747 Weighted average fair value of restricted stock granted during the year $ 9,905,986 $ 10,650,077 $ 16,061,201

Accumulated Other Comprehensi53

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income	Net unrealized gain on derivative instruments ( 1 ) SL Green’s share of joint venture net unrealized gain on derivative instruments ( 2 ) Net unrealized gain on marketable securities Total Balance at December 31, 2014 $ (9,498 ) $ (95 ) $ 2,613 $ (6,980 ) Other comprehensive loss before reclassifications (11,143 ) (1,714 ) (610 ) (13,467 ) Amounts reclassified from accumulated other comprehensive income 10,481 1,217 — 11,698 Balance at December 31, 2015 (10,160 ) (592 ) 2,003 (8,749 ) Other comprehensive income before reclassifications 13,534 1,160 3,517 18,211 Amounts reclassified from accumulated other comprehensive income 9,222 3,453 — 12,675 Balance at December 31, 2016 12,596 4,021 5,520 22,137 Other comprehensive (loss) income before reclassifications (1,618 ) 233 (1,348 ) (2,733 ) Amounts reclassified from accumulated other comprehensive income 1,564 766 (3,130 ) (800 ) Balance at December 31, 2017 $ 12,542 $ 5,020 $ 1,042 $ 18,604 (1) Amount reclassified from accumulated other comprehensive income (loss) is included in interest expense in the respective consolidated statements of operations. As of December 31, 2017 and 2016 , the deferred net losses from these terminated hedges, which is included in accumulated other comprehensive loss relating to net unrealized loss on derivative instrument, was $3.2 million and $7.1 million , respectively. (2) Amount reclassified from accumulated other comprehensive income (loss) is included in equity in net income from unconsolidated joint ventures in the respective consolidated statements of operations.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements, Recurring and Nonrecurring	The following tables set forth the assets and liabilities that we measure at fair value on a recurring and non-recurring basis by their levels in the fair value hierarchy at December 31, 2017 and 2016 (in thousands): December 31, 2017 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 28,579 $ — $ 28,579 $ — Interest rate cap and swap agreements (included in other assets) $ 16,692 $ — $ 16,692 $ — December 31, 2016 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 85,110 $ 48,315 $ 36,795 $ — Interest rate cap and swap agreements (included in other assets) $ 21,090 $ — $ 21,090 $ — Liabilities: Interest rate cap and swap agreements (included in accrued interest payable and other liabilities) $ 1 $ — $ 1 $ —
Fair Value, by Balance Sheet Grouping	The following table provides the carrying value and fair value of these financial instruments as of December 31, 2017 and December 31, 2016 (in thousands): December 31, 2017 December 31, 2016 Carrying Value (1) Fair Value Carrying Value (1) Fair Value Debt and preferred equity investments $ 2,114,041 (2) $ 1,640,412 (2) Fixed rate debt $ 4,305,165 $ 4,421,866 $ 5,452,084 $ 5,722,494 Variable rate debt 1,605,431 1,612,224 1,105,585 1,110,110 $ 5,910,596 $ 6,034,090 $ 6,557,669 $ 6,832,604 (1) Amounts exclude net deferred financing costs. (2) At December 31, 2017 , debt and preferred equity investments had an estimated fair value ranging between $2.1 billion and $2.3 billion . At December 31, 2016 , debt and preferred equity investments had an estimated fair value ranging between $1.6 billion and $1.8 billion .

Financial Instruments_ Deriva55

Financial Instruments: Derivatives and Hedging (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of notional and fair value of derivative financial instruments and foreign currency hedges	The following table summarizes the notional value at inception and fair value of our consolidated derivative financial instruments at December 31, 2017 based on Level 2 information. The notional value is an indication of the extent of our involvement in these instruments at that time, but does not represent exposure to credit, interest rate or market risks (amounts in thousands). Notional Value Strike Rate Effective Date Expiration Date Balance Sheet Location Fair Value Interest Rate Swap $ 200,000 1.131 % July 2016 July 2023 Other Assets $ 10,747 Interest Rate Swap 100,000 1.161 % July 2016 July 2023 Other Assets 5,217 Interest Rate Swap 21,394 12.000 % January 2017 January 2019 Other Assets 167 Interest Rate Cap 137,500 4.000 % September 2017 September 2019 Other Assets 2 Interest Rate Swap 100,000 1.928 % December 2017 November 2020 Other Assets 288 Interest Rate Swap 100,000 1.934 % December 2017 November 2020 Other Assets 271 $ 16,692
Schedule of effect of derivative financial instruments on consolidated statements of income	The following table presents the effect of our derivative financial instruments and our share of our joint ventures' derivative financial instruments that are designated and qualify as hedging instruments on the consolidated statements of operations for the years ended December 31, 2017 , 2016 , and 2015 , respectively (in thousands): Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion) Location of (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion) Location of (Loss) Gain Recognized in Income on Derivative Amount of (Loss) Gain Recognized into Income (Ineffective Portion) Year Ended Year Ended Year Ended Derivative 2017 2016 2015 2017 2016 2015 2017 2016 2015 Interest Rate Swaps/Caps $ (2,282 ) $ 14,616 $ (11,607 ) Interest expense $ 1,821 $ 9,521 $ 10,892 Interest expense $ 5 $ (28 ) $ (422 ) Share of unconsolidated joint ventures' derivative instruments (200 ) 2,012 (1,779 ) Equity in net income from unconsolidated joint ventures 1,035 1,981 1,265 Equity in net income from unconsolidated joint ventures 55 785 (19 ) $ (2,482 ) $ 16,628 $ (13,386 ) $ 2,856 $ 11,502 $ 12,157 $ 60 $ 757 $ (441 )

Rental Income (Tables)

Rental Income (Tables)	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Schedule of approximate future minimum rents to be received over the next five years and thereafter	Approximate future minimum rents to be received over the next five years and thereafter for non-cancelable operating leases in effect at December 31, 2017 for the consolidated properties, including consolidated joint venture properties, and our share of unconsolidated joint venture properties are as follows (in thousands): Consolidated Properties Unconsolidated Properties 2018 $ 901,092 $ 433,764 2019 865,254 386,564 2020 790,714 424,201 2021 657,283 426,078 2022 558,993 414,889 Thereafter 3,339,829 3,102,309 $ 7,113,165 $ 5,187,805

Benefit Plans (Tables)

Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Schedule of contributions made to multi-employer plans	Contributions we made to the multi-employer plans for the years ended December 31, 2017 , 2016 and 2015 are included in the table below (in thousands): Benefit Plan 2017 2016 2015 Pension Plan $ 3,856 $ 3,979 $ 2,732 Health Plan 11,426 11,530 8,736 Other plans 1,463 1,583 5,716 Total plan contributions $ 16,745 $ 17,092 $ 17,184

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	The following is a schedule of future minimum lease payments under capital leases and non-cancellable operating leases with initial terms in excess of one year as of December 31, 2017 (in thousands): Capital lease Non-cancellable operating leases 2018 $ 2,387 $ 31,049 2019 2,411 31,066 2020 2,620 31,436 2021 2,794 31,628 2022 2,794 29,472 Thereafter 819,894 703,254 Total minimum lease payments $ 832,900 $ 857,905 Amount representing interest (790,057 ) Capital lease obligations $ 42,843
Schedule of Future Minimum Lease Payments for Capital Leases	The following is a schedule of future minimum lease payments under capital leases and non-cancellable operating leases with initial terms in excess of one year as of December 31, 2017 (in thousands): Capital lease Non-cancellable operating leases 2018 $ 2,387 $ 31,049 2019 2,411 31,066 2020 2,620 31,436 2021 2,794 31,628 2022 2,794 29,472 Thereafter 819,894 703,254 Total minimum lease payments $ 832,900 $ 857,905 Amount representing interest (790,057 ) Capital lease obligations $ 42,843

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Schedule of selected results of operations and selected asset information	Selected results of operations for the years ended December 31, 2017 , 2016 , and 2015 , and selected asset information as of December 31, 2017 and 2016 , regarding our operating segments are as follows (in thousands): Real Estate Segment Debt and Preferred Equity Segment Total Company Total revenues Years ended: December 31, 2017 $ 1,317,602 $ 193,871 $ 1,511,473 December 31, 2016 1,650,973 213,008 1,863,981 December 31, 2015 1,481,701 181,128 1,662,829 Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and gain (loss) on sale of marketable securities Years ended: December 31, 2017 $ 16,557 $ 170,363 $ 186,920 December 31, 2016 (197,000 ) 204,256 7,256 December 31, 2015 (71,634 ) 161,923 90,289 Total assets As of: December 31, 2017 $ 11,696,560 $ 2,286,344 $ 13,982,904 December 31, 2016 13,868,672 1,989,115 15,857,787
Schedule of reconciliation of income from continuing operations to net income attributable to SL Green common stockholders	The table below reconciles income from continuing operations to net income for the years ended December 31, 2017 , 2016 , and 2015 (in thousands): Year ended December 31, 2017 2016 2015 Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and gain (loss) on sale of marketable securities $ 186,920 $ 7,256 $ 90,289 Equity in net gain on sale of interest in unconsolidated joint venture/real estate 16,166 44,009 15,844 Purchase price fair value adjustment — — 40,078 Gain on sale of real estate, net 73,241 238,116 175,974 Depreciable real estate reserves (178,520 ) (10,387 ) (19,226 ) Loss on early extinguishment of debt — — (49 ) Gain (loss) on sale of investment in marketable securities 3,262 (83 ) — Income from continuing operations 101,069 278,911 302,910 Net income from discontinued operations — — 427 Gain on sale of discontinued operations — — 14,122 Net income $ 101,069 $ 278,911 $ 317,459

Quarterly Financial Data of t60

Quarterly Financial Data of the Company (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
SL Green Realty Corp
Condensed Income Statements, Captions [Line Items]
Schedule of Quarterly Financial Information	Summarized quarterly financial data for the years ended December 31, 2017 and 2016 was as follows (in thousands, except for per share amounts): 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 — $ 398,150 — $ 377,381 Income from continuing operations before equity in net income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain (loss) on sale of real estate, depreciable real estate reserves and gain on the sale of investment in marketable securities $ 47,234 $ 40,687 — $ 32,401 — $ 44,706 Equity in net income from unconsolidated joint ventures 7,788 4,078 — 3,412 — 6,614 Equity in net gain on sale of interest in unconsolidated joint venture/real estate — 1,030 — 13,089 — 2,047 Gain (loss) on sale of real estate, net 76,497 — — (3,823 ) — 567 Depreciable real estate reserves (93,184 ) — — (29,064 ) — (56,272 ) Gain on the sale of investment in marketable securities — — — — — 3,262 Noncontrolling interests and preferred unit distributions (6,616 ) (3,188 ) — (4,056 ) — 14,165 Net income attributable to SL Green 31,719 42,607 11,959 15,089 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) — (3,738 ) Net income attributable to SL Green common stockholders $ 27,982 $ 38,869 $ 8,222 $ 11,351 Net income attributable to common stockholders per common share—basic $ 0.29 $ 0.40 — $ 0.08 — $ 0.11 Net income attributable to common stockholders per common share—diluted $ 0.29 $ 0.40 — $ 0.08 — $ 0.11 2016 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 374,242 $ 416,681 $ 617,614 $ 455,444 Income (loss) from continuing operations before equity in net (loss) income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, depreciable real estate reserves and loss on sale of marketable securities $ 26,278 $ 46,689 $ (76,304 ) $ (1,281 ) Equity in net (loss) income from unconsolidated joint ventures (95 ) (3,968 ) 5,841 10,096 Equity in net gain on sale of interest in unconsolidated joint venture/real estate 421 225 33,448 9,915 Gain on sale of real estate, net 27,366 397 196,580 13,773 Depreciable real estate reserves — — (10,387 ) — Loss on the sale of investment in marketable securities — — (83 ) — Noncontrolling interests and preferred unit distributions (6,217 ) (5,353 ) (11,901 ) (5,544 ) Net income attributable to SL Green 47,753 37,990 137,194 26,959 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income attributable to SL Green common stockholders $ 44,016 $ 34,252 $ 133,457 $ 23,221 Net income attributable to common stockholders per common share—basic $ 0.44 $ 0.34 $ 1.33 $ 0.23 Net income attributable to common stockholders per common share—diluted $ 0.44 $ 0.34 $ 1.33 $ 0.23

Quarterly Financial Data of t61

Quarterly Financial Data of the Operating Partnership (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
SL Green Operating Partnership
Condensed Income Statements, Captions [Line Items]
Schedule of Quarterly Financial Information	Summarized quarterly financial data for the years ended December 31, 2017 and 2016 was as follows (in thousands, except for per share amounts): 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 — $ 398,150 — $ 377,381 Income from continuing operations before equity in net income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain (loss) on sale of real estate, depreciable real estate reserves and gain on the sale of investment in marketable securities $ 47,234 $ 40,687 — $ 32,401 — $ 44,706 Equity in net income from unconsolidated joint ventures 7,788 4,078 — 3,412 — 6,614 Equity in net gain on sale of interest in unconsolidated joint venture/real estate — 1,030 — 13,089 — 2,047 Gain (loss) on sale of real estate, net 76,497 — — (3,823 ) — 567 Depreciable real estate reserves (93,184 ) — — (29,064 ) — (56,272 ) Gain on the sale of investment in marketable securities — — — — — 3,262 Noncontrolling interests and preferred unit distributions (5,328 ) (1,376 ) — (3,637 ) — 14,641 Net income attributable to SLGOP 33,007 44,419 — 12,378 15,565 Perpetual preferred units distributions (3,737 ) (3,738 ) — (3,737 ) — (3,738 ) Net income attributable to SLGOP common unitholders $ 29,270 $ 40,681 — $ 8,641 $ 11,827 Net income attributable to common unitholders per common unit—basic $ 0.29 $ 0.40 — $ 0.08 — $ 0.11 Net income attributable to common unitholders per common unit—diluted $ 0.29 $ 0.40 — $ 0.08 — $ 0.11 2016 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 374,242 $ 416,681 $ 617,614 $ 455,444 Income (loss) from continuing operations before equity in net (loss) income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, depreciable real estate reserves and loss on the sale of investment in marketable securities $ 26,278 $ 46,689 $ (76,304 ) $ (1,281 ) Equity in net (loss) income from unconsolidated joint ventures (95 ) (3,968 ) 5,841 10,096 Equity in net gain on sale of interest in unconsolidated joint venture/real estate 421 225 33,448 9,915 Gain on sale of real estate, net 27,366 397 196,580 13,773 Depreciable real estate reserves — — (10,387 ) — Loss on the sale of investment in marketable securities — — (83 ) — Noncontrolling interests and preferred unit distributions (4,252 ) (3,690 ) (6,315 ) (4,622 ) Net income attributable to SLGOP 49,718 39,653 142,780 27,881 Perpetual preferred units distributions (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income attributable to SLGOP common unitholders $ 45,981 $ 35,915 $ 139,043 $ 24,143 Net income attributable to common unitholders per common unit—basic $ 0.44 $ 0.34 $ 1.33 $ 0.23 Net income attributable to common unitholders per common unit—diluted $ 0.44 $ 0.34 $ 1.33 $ 0.23

Organization and Basis of Pre62

Organization and Basis of Presentation - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017shares
Organization
Number of shares to be received on redemption of one unit of limited partnership interests (shares)	1
SL Green Operating Partnership | Service Corporation
Organization
Economic interest in variable interest entity (as a percent)	95.00%
SL Green Management
Organization
Percentage of ownership in SL Green Management LLC owned by operating partnership (percent)	100.00%

Organization and Basis of Pre63

Organization and Basis of Presentation - Schedule of Commercial Office Properties (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)ft²buildingshares	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Real estate properties
Number of Properties | building	98
Approximate Square Feet unaudited (sqft)	33,253,213
Mortgage Loans on Real Estate, Commercial and Consumer, Net Including Debt Investments, Other | $	$ 2,114,041	$ 1,640,412	$ 1,670,020
Weighted Average Occupancy unaudited (as a percent)	91.40%
Number of shares to be received on redemption of one unit of limited partnership interests (shares) | shares	1
Commercial properties
Real estate properties
Number of Properties | building	83
Approximate Square Feet unaudited (sqft)	30,124,252
Weighted Average Occupancy unaudited (as a percent)	91.80%
Residential
Real estate properties
Number of Properties | building	15
Approximate Square Feet unaudited (sqft)	3,128,961
Weighted Average Occupancy unaudited (as a percent)	87.60%
Managed office properties
Real estate properties
Approximate Square Feet unaudited (sqft)	336,000
Mortgage Loans on Real Estate, Commercial and Consumer, Net Including Debt Investments, Other | $	$ 2,300,000
Debt Investments, Other | $	$ 200,000
Consolidated properties
Real estate properties
Number of Properties | building	60
Approximate Square Feet unaudited (sqft)	18,481,009
Consolidated properties | Commercial properties
Real estate properties
Number of Properties | building	57
Approximate Square Feet unaudited (sqft)	18,008,904
Consolidated properties | Residential
Real estate properties
Number of Properties | building	3
Approximate Square Feet unaudited (sqft)	472,105
Unconsolidated properties
Real estate properties
Number of Properties | building	38
Approximate Square Feet unaudited (sqft)	14,772,204
Unconsolidated properties | Commercial properties
Real estate properties
Number of Properties | building	26
Approximate Square Feet unaudited (sqft)	12,115,348
Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	12
Approximate Square Feet unaudited (sqft)	2,656,856
Manhattan
Real estate properties
Number of Properties | building	58
Approximate Square Feet unaudited (sqft)	26,418,052
Weighted Average Occupancy unaudited (as a percent)	92.90%
Manhattan | Office
Real estate properties
Number of Properties | building	32
Approximate Square Feet unaudited (sqft)	24,661,470
Weighted Average Occupancy unaudited (as a percent)	93.90%
Manhattan | Retail
Real estate properties
Number of Properties | building	13
Approximate Square Feet unaudited (sqft)	650,553
Weighted Average Occupancy unaudited (as a percent)	94.50%
Manhattan | Development/Redevelopment
Real estate properties
Number of Properties | building	11
Approximate Square Feet unaudited (sqft)	929,499
Weighted Average Occupancy unaudited (as a percent)	63.80%
Manhattan | Fee Interest
Real estate properties
Number of Properties | building	2
Approximate Square Feet unaudited (sqft)	176,530
Weighted Average Occupancy unaudited (as a percent)	100.00%
Manhattan | Residential
Real estate properties
Number of Properties | building	15
Approximate Square Feet unaudited (sqft)	3,128,961
Weighted Average Occupancy unaudited (as a percent)	87.60%
Manhattan | Consolidated properties
Real estate properties
Number of Properties | building	35
Approximate Square Feet unaudited (sqft)	14,942,704
Manhattan | Consolidated properties | Office
Real estate properties
Number of Properties | building	23
Approximate Square Feet unaudited (sqft)	14,304,606
Manhattan | Consolidated properties | Retail
Real estate properties
Number of Properties | building	4
Approximate Square Feet unaudited (sqft)	302,583
Manhattan | Consolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	7
Approximate Square Feet unaudited (sqft)	158,985
Manhattan | Consolidated properties | Fee Interest
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	176,530
Manhattan | Consolidated properties | Residential
Real estate properties
Number of Properties | building	3
Approximate Square Feet unaudited (sqft)	472,105
Manhattan | Consolidated properties | Dual property type, retail portion
Real estate properties
Approximate Square Feet unaudited (sqft)	270,132
Manhattan | Consolidated properties | Dual property type, residential portion
Real estate properties
Approximate Square Feet unaudited (sqft)	222,855
Manhattan | Unconsolidated properties
Real estate properties
Number of Properties | building	23
Approximate Square Feet unaudited (sqft)	11,475,348
Manhattan | Unconsolidated properties | Office
Real estate properties
Number of Properties | building	9
Approximate Square Feet unaudited (sqft)	10,356,864
Manhattan | Unconsolidated properties | Retail
Real estate properties
Number of Properties | building	9
Approximate Square Feet unaudited (sqft)	347,970
Manhattan | Unconsolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	4
Approximate Square Feet unaudited (sqft)	770,514
Manhattan | Unconsolidated properties | Fee Interest
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	0
Manhattan | Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	12
Approximate Square Feet unaudited (sqft)	2,656,856
Suburban
Real estate properties
Number of Properties | building	25
Approximate Square Feet unaudited (sqft)	3,706,200
Weighted Average Occupancy unaudited (as a percent)	84.30%
Suburban | Office
Real estate properties
Number of Properties | building	22
Approximate Square Feet unaudited (sqft)	3,653,200
Weighted Average Occupancy unaudited (as a percent)	84.00%
Suburban | Retail
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	52,000
Weighted Average Occupancy unaudited (as a percent)	100.00%
Suburban | Development/Redevelopment
Real estate properties
Number of Properties | building	2
Approximate Square Feet unaudited (sqft)	1,000
Weighted Average Occupancy unaudited (as a percent)	100.00%
Suburban | Residential
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0
Weighted Average Occupancy unaudited (as a percent)	0.00%
Suburban | Consolidated properties
Real estate properties
Number of Properties | building	22
Approximate Square Feet unaudited (sqft)	3,066,200
Suburban | Consolidated properties | Office
Real estate properties
Number of Properties | building	20
Approximate Square Feet unaudited (sqft)	3,013,200
Suburban | Consolidated properties | Retail
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	52,000
Suburban | Consolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	1,000
Suburban | Consolidated properties | Residential
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0
Suburban | Unconsolidated properties
Real estate properties
Number of Properties | building	3
Approximate Square Feet unaudited (sqft)	640,000
Suburban | Unconsolidated properties | Office
Real estate properties
Number of Properties | building	2
Approximate Square Feet unaudited (sqft)	640,000
Suburban | Unconsolidated properties | Retail
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0
Suburban | Unconsolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	0
Suburban | Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0

Significant Accounting Polici64

Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Principles of Consolidation
Commercial real estate properties	$ 7,906,006	$ 10,478,638
Mortgages and other loans payable, net	2,837,282	4,073,830
Assets held for sale	338,354	0
Liabilities related to assets held for sale	4,074	0
Consolidated VIEs
Principles of Consolidation
Mortgages and other loans payable, net	$ 628,900	$ 621,800

Significant Accounting Polici65

Significant Accounting Policies - Investments in Commercial Real Estate Properties (Details) - USD ($) $ in Thousands	Nov. 30, 2015	Dec. 31, 2015	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate [Line Items]
Depreciation expense (including amortization of the capital lease asset)					$ 365,300	$ 783,500	$ 523,800
Impairment Charge				$ 10,400
Period from cessation of major construction to consider construction project as complete and available for occupancy, maximum (in years)					1 year
Weighted average amortization period for above-market leases (in years)					6 years
Weighted average amortization period for below-market leases (in years)					23 years 4 months
Weighted average amortization for in-place lease costs (in years)					16 years 4 months
Amortization of above and below Market Leases					$ 20,300	196,200	38,700
Reduction in interest expense from amortization of above-market rate mortgages					800	2,800	$ 2,300
Identified intangible assets (included in other assets):
Gross amount					325,880	651,099
Accumulated amortization					(277,038)	(410,930)
Net					48,842	240,169
Identified intangible liabilities (included in deferred revenue):
Gross amount					540,283	655,930
Accumulated amortization					(402,583)	(464,749)
Net					137,700	$ 191,181
Net intangible assets reclassed to assets held for sale					13,900
Net intangible liabilities reclassed to liabilities relates to assets held for sale					4,100
Other Identifiable Assets
Estimated annual amortization
2,018					9,700
2,019					7,716
2,020					6,783
2,021					3,927
2,022					2,365
Acquired above-market leases, net of acquired below-market leases
Below Market Lease, Net, Amortization Income, Fiscal Year Maturity [Abstract]
2,018					(13,853)
2,019					(13,250)
2,020					(12,432)
2,021					(3,950)
2,022					$ (3,647)
600 Lexington Avenue
Real Estate [Line Items]
Purchase price fair value adjustment realized	$ 40,078	$ 40,100
Maximum | Above-market leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)					14 years
Maximum | Below-market leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)					14 years
Maximum | In-place leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)					14 years
Minimum | Above-market leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)					1 year
Minimum | Below-market leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)					1 year
Minimum | In-place leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)					1 year
Building (fee ownership)
Real Estate [Line Items]
Estimated useful life (in years)					40 years
Building (leasehold interest) | Maximum
Real Estate [Line Items]
Estimated useful life (in years)					40 years
Furniture and fixtures | Maximum
Real Estate [Line Items]
Estimated useful life (in years)					7 years
Furniture and fixtures | Minimum
Real Estate [Line Items]
Estimated useful life (in years)					4 years
Building | Maximum
Real Estate [Line Items]
Estimated useful life (in years)					40 years
Building | Minimum
Real Estate [Line Items]
Estimated useful life (in years)					3 years
140-150 Grand Street
Real Estate [Line Items]
Impairment Charge			$ 19,200
388-390 Greenwich Street
Real Estate [Line Items]
Amortization of below market leases					$ 172,400

Significant Accounting Polici66

Significant Accounting Policies - Investment in Marketable Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment in Marketable Securities
Marketable securities	$ 28,579,000	$ 85,110,000
Proceeds from sale of marketable securities	55,129,000	6,965,000	$ 1,426,000
Realized gain (loss) on investment in marketable securities	3,300,000	100,000
Fair Value
Investment in Marketable Securities
Marketable securities	28,579,000	85,110,000
Equity marketable securities
Investment in Marketable Securities
Marketable securities	0	48,315,000
Cost basis	0	43,300,000
Mortgage-backed securities
Investment in Marketable Securities
Marketable securities	28,579,000	36,795,000
Cost basis	$ 27,500,000	$ 36,000,000

Significant Accounting Polici67

Significant Accounting Policies - Investments in Unconsolidated Joint Ventures/Deferred Lease Costs/Revenue Recognition/Income Taxes (Details)	12 Months Ended
	Dec. 31, 2017USD ($)joint_venture$ / shares	Dec. 31, 2016USD ($)$ / shares	Dec. 31, 2015USD ($)$ / shares
Schedule of Equity Method Investments [Line Items]
Number of joint ventures with performance guarantees under master leases | joint_venture	2
Deferred Lease Costs [Abstract]
Portion of compensation capitalized	$ 16,400,000	$ 15,400,000	$ 15,400,000
Estimated average lease term (in years)	7 years
Days past due for income recognition on debt and preferred equity investments to be suspended	90 days
Loan reserves recorded	$ 0	0	0
Income taxes
Federal, state and local tax provision	4,300,000	2,800,000	3,100,000
Interest Expense Increase (Decrease) Assumed Above Market Rate Mortgage Amortization	$ (800,000)	$ (2,800,000)	$ (2,300,000)
Dividends per share paid (in dollars per share) | $ / shares	$ 3.100000	$ 2.880000	$ 2.400000
Ordinary Income Dividend
Income taxes
Dividends per share paid (in dollars per share) | $ / shares	1.236708	2.482236	0
Capital Gains Dividend
Income taxes
Dividends per share paid (in dollars per share) | $ / shares	$ 1.863292	$ 0.40	$ 2.40000

Significant Accounting Polici68

Significant Accounting Policies - Concentrations of Credit Risk/Reclassification (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Tenantagreement	Dec. 31, 2016USD ($)	Dec. 31, 2015
Concentration of Credit Risk
Common shares	$ 939	$ 1,017
Additional paid-in-capital	4,968,338	5,624,545
Treasury shares	(124,049)	(124,049)
Retained earnings	$ 1,139,329	$ 1,578,893
Annualized rent | Customer concentration
Concentration of Credit Risk
Number of tenants (tenants) | Tenant	1
Maximum percentage of annualized rent for any one tenant not individually disclosed (percent) (more than)	5.00%
Annualized rent | 1515 Broadway | Customer concentration
Concentration of Credit Risk
Percentage of concentration	7.00%	8.80%	8.90%
Annualized rent | 388-390 Greenwich Street | Customer concentration
Concentration of Credit Risk
Percentage of concentration		6.90%	8.20%
Annualized rent | 919 Third Avenue | Customer concentration
Concentration of Credit Risk
Percentage of concentration		6.10%	6.50%
Annualized rent | 1185 Avenue of the Americas | Customer concentration
Concentration of Credit Risk
Percentage of concentration	7.10%	5.90%	6.60%
Annualized rent | 11 Madison Avenue | Customer concentration
Concentration of Credit Risk
Percentage of concentration	7.10%	5.60%
Annualized rent | 420 Lexington Avenue | Customer concentration
Concentration of Credit Risk
Percentage of concentration	6.00%		5.60%
Annualized rent | 1 Madison Ave | Customer concentration
Concentration of Credit Risk
Percentage of concentration	5.60%
Collective bargaining arrangements | Workforce concentration
Concentration of Credit Risk
Percentage of concentration	68.40%
Number of collective bargaining agreements | agreement	6
Collective bargaining arrangements expiring in December 2018 | Workforce concentration
Concentration of Credit Risk
Percentage of concentration	8.80%
Collective bargaining arrangements expiring in December 2019 | Workforce concentration
Concentration of Credit Risk
Percentage of concentration	55.00%
Tenant 1 | Annualized rent | Customer concentration
Concentration of Credit Risk
Percentage of concentration	8.00%

Significant Accounting Polici69

Significant Accounting Policies - Accounting Standards Update (Details) $ in Billions	3 Months Ended
	Mar. 31, 2018USD ($)
Scenario, Forecast | 1515 Broadway | Accounting Standards Update 2017-05
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gain on disposal	$ 0.6

Property Acquisitions - Additio

Property Acquisitions - Additional Information (Details) - USD ($) $ in Thousands	Nov. 30, 2015	Mar. 31, 2016	Dec. 31, 2015	Aug. 31, 2015	Jul. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2017	Jun. 30, 2016
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units								$ 221,932	$ 221,932
Impact to rental revenue for amortization of aggregate below-market leases								1,100,993	1,323,767	$ 1,245,981
Impact to depreciation expense								403,320	821,041	$ 560,887
600 Lexington Ave | As Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land									97,000
Building and building leasehold									$ 180,200
183 Broadway
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land											$ 5,799
Building and building leasehold											23,431
Above market lease value											0
Acquired in-place leases											773
Other assets, net of other liabilities											20
Assets acquired											30,023
Mark-to-market assumed debt											0
Below market lease value											(1,523)
Derivatives											0
Liabilities assumed											(1,523)
Purchase price											$ 28,500
Net consideration funded by us at closing, excluding consideration financed by debt		$ 28,500
Equity and/or debt investment held		0
Debt assumed		0
600 Lexington Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land								81,670
Building and building leasehold								182,447
Above market lease value								3,320
Acquired in-place leases								22,449
Other assets, net of other liabilities								0
Assets acquired								289,886
Mark-to-market assumed debt								(55)
Below market lease value								(5,831)
Derivatives								0
Liabilities assumed								(5,886)
Purchase price	$ 284,000							$ 284,000
Net consideration funded by us at closing, excluding consideration financed by debt	79,085		$ 79,085
Equity and/or debt investment held	54,575		54,575
Debt assumed	112,795		112,795
Ownership interest in consolidated joint venture (as a percent)								45.00%
Value of interest								$ 277,300
Purchase price fair value adjustment	$ 40,078		$ 40,100
183, 187 Broadway & 5-7 Dey Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				$ 20,266
Building and building leasehold				42,468
Above market lease value				17
Acquired in-place leases				3,621
Other assets, net of other liabilities				0
Assets acquired				66,372
Mark-to-market assumed debt				0
Below market lease value				(3,226)
Derivatives				0
Liabilities assumed				(3,226)
Purchase price				63,146
Net consideration funded by us at closing, excluding consideration financed by debt				0
Equity and/or debt investment held				0
Debt assumed				0
183, 187 Broadway & 5-7 Dey Street | As Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				22,100
Building and building leasehold				41,000
183, 187 Broadway & 5-7 Dey Street | Series R Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units								10,000
183, 187 Broadway & 5-7 Dey Street | Series S Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units								$ 26,900
11 Madison Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				675,776
Building and building leasehold				1,553,602
Above market lease value				19,764
Acquired in-place leases				366,949
Other assets, net of other liabilities				0
Assets acquired				2,616,091
Mark-to-market assumed debt				0
Below market lease value				(187,732)
Derivatives				0
Liabilities assumed				(187,732)
Purchase price				2,428,359
Net consideration funded by us at closing, excluding consideration financed by debt				0
Equity and/or debt investment held				0
Debt assumed				0
11 Madison Avenue | As Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				849,900
Building and building leasehold				$ 1,600,000
110 Greene Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land					$ 45,120
Building and building leasehold					215,470
Above market lease value					0
Acquired in-place leases					8,967
Other assets, net of other liabilities					0
Assets acquired					269,557
Mark-to-market assumed debt					0
Below market lease value					(14,557)
Derivatives					0
Liabilities assumed					(14,557)
Purchase price					255,000
Net consideration funded by us at closing, excluding consideration financed by debt					0
Equity and/or debt investment held					0
Debt assumed					$ 0
Ownership interest in consolidated joint venture (as a percent)					90.00%
110 Greene Street | As Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land					$ 89,300
Building and building leasehold					165,800
110 Greene Street | Series P Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units					5,000
110 Greene Street | Series Q Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units					$ 6,700
Upper East Side Residential
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land												$ 48,152
Building and building leasehold												0
Above market lease value												0
Acquired in-place leases												1,922
Other assets, net of other liabilities												0
Assets acquired												50,074
Mark-to-market assumed debt												0
Below market lease value												0
Derivatives												0
Liabilities assumed												0
Purchase price												$ 50,074
Net consideration funded by us at closing, excluding consideration financed by debt						$ 0
Equity and/or debt investment held						0
Debt assumed						$ 0
Ownership interest in consolidated joint venture (as a percent)												95.10%
Upper East Side Residential | Series N Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units												$ 13,800
1640 Flatbush Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land		6,226
Building and building leasehold		501
Above market lease value		0
Acquired in-place leases		146
Other assets, net of other liabilities		0
Assets acquired		6,873
Mark-to-market assumed debt		0
Below market lease value		(73)
Derivatives		0
Liabilities assumed		(73)
Purchase price		6,800
Net consideration funded by us at closing, excluding consideration financed by debt							$ 0
Equity and/or debt investment held							0
Debt assumed							$ 0
1640 Flatbush Avenue | As Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land		6,100
Building and building leasehold		$ 700

Property Acquisitions - Schedul

Property Acquisitions - Schedule of Fair Value of Equity Interest Immediately Before Acquisition Date (Details) - USD ($) $ in Thousands	Nov. 30, 2015	Dec. 31, 2015	Aug. 31, 2015	Jul. 31, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2016	Mar. 31, 2016
Property Acquisitions
Operating Leases, Income Statement, Minimum Lease Revenue						$ 1,100,993	$ 1,323,767	$ 1,245,981
Depreciation and amortization						403,320	821,041	$ 560,887
183, 187 Broadway & 5-7 Dey Street
Property Acquisitions
Land			$ 20,266
Building and building leasehold			42,468
Contract purchase price			63,146
Net consideration funded by us at closing, excluding consideration financed by debt			0
Debt assumed			0
Equity and/or debt investment held			0
600 Lexington Avenue
Property Acquisitions
Land						81,670
Building and building leasehold						182,447
Contract purchase price	$ 284,000					$ 284,000
Net consideration funded by us at closing, excluding consideration financed by debt	(79,085)	$ (79,085)
Debt assumed	(112,795)	(112,795)
Fair value of retained equity interest	92,120
Equity and/or debt investment held	(54,575)	(54,575)
Other	2,533
Purchase price fair value adjustment	$ 40,078	$ 40,100
11 Madison Avenue
Property Acquisitions
Land			675,776
Building and building leasehold			1,553,602
Contract purchase price			2,428,359
Net consideration funded by us at closing, excluding consideration financed by debt			0
Debt assumed			0
Equity and/or debt investment held			0
110 Greene Street
Property Acquisitions
Land				$ 45,120
Building and building leasehold				215,470
Contract purchase price				255,000
Net consideration funded by us at closing, excluding consideration financed by debt				0
Debt assumed				0
Equity and/or debt investment held				0
1640 Flatbush Avenue
Property Acquisitions
Land										$ 6,226
Building and building leasehold										501
Contract purchase price										6,800
Net consideration funded by us at closing, excluding consideration financed by debt					$ 0
Debt assumed					0
Equity and/or debt investment held					$ 0
Upper East Side Residential, 11 Madison Avenue, 600 Lexington Ave, 187 Broadway and 5 & 7 Dey Street, 110 Greene Street and 1640 Flatbush Avenue
Property Acquisitions
Operating Leases, Income Statement, Minimum Lease Revenue							7,800
Depreciation and amortization							$ 18,500
As Previously Reported | 183, 187 Broadway & 5-7 Dey Street
Property Acquisitions
Land			22,100
Building and building leasehold			41,000
As Previously Reported | 11 Madison Avenue
Property Acquisitions
Land			849,900
Building and building leasehold			$ 1,600,000
As Previously Reported | 110 Greene Street
Property Acquisitions
Land				89,300
Building and building leasehold				$ 165,800
As Previously Reported | Upper East Side Residential
Property Acquisitions
Land									$ 17,500
Building and building leasehold									$ 32,500
As Previously Reported | 1640 Flatbush Avenue
Property Acquisitions
Land										6,100
Building and building leasehold										$ 700

Property Acquisitions - Pro For

Property Acquisitions - Pro Forma (Details) - 11 Madison Avenue $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)$ / shares
Property Acquisitions
Actual revenues since acquisition	$ 29,865
Actual net income since acquisition	159
Pro forma revenues	1,657,937
Pro forma income from continuing operations	$ 102,440
Pro forma basic earnings per share (in usd per share) | $ / shares	$ 0.76
Pro forma diluted earnings per share (in usd per share) | $ / shares	$ 0.75
Mortgage loan
Property Acquisitions
Fixed rate debt	$ 1,400,000
Initial Term (in Years)	10 years
Interest rate, fixed rate debt (as a percent)	3.838%
SL Green Operating Partnership
Property Acquisitions
Pro forma basic earnings per share (in usd per share) | $ / shares	$ 0.76
Pro forma diluted earnings per share (in usd per share) | $ / shares	$ 0.75

Properties Held for Sale and 73

Properties Held for Sale and Property Dispositions - Properties Held for Sale (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Jun. 30, 2016	Jan. 31, 2018	Sep. 30, 2017	Apr. 30, 2017	Mar. 31, 2017
Property Dispositions and Assets Held for Sale
Impairment Charge		$ 10,400
115-117 Stevens Avenue
Property Dispositions and Assets Held for Sale
Impairment Charge	$ 17,800
1-6 International Drive
Property Dispositions and Assets Held for Sale
Impairment Charge	$ 69,100
102 Greene Street
Property Dispositions and Assets Held for Sale
Gross asset valuation				$ 43,500	$ 43,500
Ownership interest classified as held for sale						90.00%
Subsequent Event | 600 Lexington Avenue
Property Dispositions and Assets Held for Sale
Gross asset valuation			$ 305,000

Properties Held for Sale and 74

Properties Held for Sale and Property Dispositions - Property Dispositions (Details) $ in Thousands	1 Months Ended																	3 Months Ended					12 Months Ended
	Feb. 22, 2018	Dec. 31, 2017USD ($)ft²	Nov. 30, 2017	Oct. 31, 2017USD ($)ft²	Sep. 30, 2017USD ($)	Jul. 31, 2017USD ($)ft²	Apr. 30, 2017USD ($)ft²	Oct. 31, 2016USD ($)ft²	Aug. 31, 2016USD ($)ft²	Jul. 31, 2016USD ($)ft²	Jun. 30, 2016USD ($)ft²	May 31, 2016USD ($)a	Feb. 29, 2016USD ($)ft²	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Aug. 31, 2015USD ($)ft²	Jan. 31, 2015USD ($)ft²	Dec. 31, 2017USD ($)ft²	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Sep. 30, 2016USD ($)ft²	Jun. 30, 2016USD ($)ft²	Dec. 31, 2017USD ($)ft²	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²		33,253,213																33,253,213					33,253,213
Gain on Sale																							$ 0	$ 0	$ 14,122
Employee compensation award																		$ 900	$ 2,500				0	1,100	1,200
Impairment Charge																						$ 10,400
Revenues
Rental revenue																							0	0	236
Escalation and reimbursement revenues																							0	0	(127)
Other income																							0	0	0
Total revenues																							0	0	109
Operating expenses																							0	0	(631)
Real estate taxes																							0	0	250
Ground rent																							0	0	0
Transaction related costs																							0	0	(49)
Interest expense, net of interest income																							0	0	109
Amortization of deferred financing costs																							0	0	3
Depreciation and amortization																							0	0	0
Total expenses																							0	0	(318)
Net income from discontinued operations																							$ 0	$ 0	$ 427
1515 Broadway
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²		1,750,000																1,750,000					1,750,000
Gross asset valuation		$ 1,950,000																$ 1,950,000					$ 1,950,000
Gain on Sale		$ 0
Joint venture ownership percentage sold			30.13%
125 Chubb Way
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²				278,000
Gross asset valuation				$ 29,500
Gain on Sale				$ (26,100)
Impairment Charge																			$ 26,100
16 Court Street
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²				317,600
Gross asset valuation				$ 171,000
Gain on Sale				$ 64,900
680-750 Washington Boulevard
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²						325,000
Gross asset valuation						$ 97,000
Gain on Sale						$ (44,200)
Impairment Charge																				$ 44,200
520 White Plains Road
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²							180,000
Gross asset valuation							$ 21,000
Gain on Sale							$ (14,600)
Impairment Charge																				$ 14,600
102 Greene Street
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²							9,200
Gross asset valuation					$ 43,500		$ 43,500
Gain on Sale							$ 4,900
Joint venture ownership percentage sold					10.00%		90.00%
400 East 57th Street
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²								290,482
Gross asset valuation								$ 83,300
Gain on Sale								23,900
Employee compensation award								$ 1,000
Ownership percentage in disposed asset								49.00%
11 Madison Avenue
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²									2,314,000
Gross asset valuation									$ 2,605,000
Gain on Sale									3,600
Employee compensation award									$ 600
Ownership percentage in disposed asset									40.00%
500 West Putnam Avenue
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²										121,500
Gross asset valuation										$ 41,000
Gain on Sale										$ (10,400)
388 Greenwich
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²											2,635,000											2,635,000
Gross asset valuation											$ 2,002,300											$ 2,002,300
Gain on Sale											206,500
Employee compensation award											$ 1,600
7 International Drive
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | a												31
Gross asset valuation												$ 20,000
Gain on Sale												$ (6,900)
248-252 Bedford Avenue
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²													66,611
Gross asset valuation													$ 55,000
Gain on Sale													15,300
Employee compensation award													$ 1,300
885 Third Avenue
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²													607,000
Gross asset valuation													$ 453,000
Gain on Sale													$ (8,800)
140-150 Grand Street
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²		215,100																215,100					215,100
Gross asset valuation		$ 32,000																$ 32,000					$ 32,000
Gain on Sale														$ (20,100)
Impairment Charge																					$ 19,200
570 & 574 Fifth Avenue
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²		24,327																24,327					24,327
Gross asset valuation		$ 125,400																$ 125,400					$ 125,400
Gain on Sale														24,600
Employee compensation award														$ 4,000
120 West 45th Street
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²																					440,000
Gross asset valuation																					$ 365,000
Gain on Sale															$ 58,600
Employee compensation award															$ 2,000
131-137 Spring Street
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²																68,342
Gross asset valuation																$ 277,800
Gain on Sale																101,100
Employee compensation award																$ 4,100
Ownership percentage in disposed asset																80.00%
180 Maiden Lane
Properties Sold [Abstract]
(unaudited) Approximate Usable Square Feet | ft²																	1,090,000
Gross asset valuation																	$ 470,000
Gain on Sale																	17,000
Employee compensation award																	$ 800
Subsequent Event | 1515 Broadway
Properties Sold [Abstract]
Joint venture ownership percentage sold	12.87%

Debt and Preferred Equity Inv75

Debt and Preferred Equity Investments - Roll Forward of Net Book Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Mortgage Loans on Real Estate [Line Items]
Balance at beginning of period	$ 1,640,412	$ 1,670,020
Redemptions/sales/syndications/amortization	(813,418)	(1,044,482)
Balance at end of period	2,114,041	1,640,412
Debt investment
Mortgage Loans on Real Estate [Line Items]
Originations/accretion	1,142,591	1,009,176
Preferred equity investments
Mortgage Loans on Real Estate [Line Items]
Originations/accretion	$ 144,456	$ 5,698

Debt and Preferred Equity Inv76

Debt and Preferred Equity Investments - Debt Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	May 31, 2017	Dec. 31, 2016	Sep. 30, 2014
Mortgage Loans on Real Estate [Line Items]
Mortgage loans on real estate, interest rate	9.31%
Debt Investments Held [Abstract]
Carrying Value	$ 2,114,041		$ 1,640,412
Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Amount participated out	1,200
Mezzanine Loan with an Initial Maturity Date of June 2024
Debt Investments Held [Abstract]
Amount participated out	12,000
Mezzanine Loan with an Initial Maturity of March 2018
Debt Investments Held [Abstract]
Amount participated out	5,100
Mezzanine Loan with an Initial Maturity Date of December 2018
Debt Investments Held [Abstract]
Amount participated out	14,600
Mezzanine Loan with an Initial Maturity Date of December 2018, 2
Debt Investments Held [Abstract]
Amount participated out	14,100
Mezzanine Loan with an Initial Maturity Date of January 2019
Debt Investments Held [Abstract]
Amount participated out	$ 21,200
Mezzanine Loan Contributed To Joint Venture In May 2017
Debt Investments Held [Abstract]
Equity Method Investment, Ownership Percentage	33.33%	33.33%
Debt investment
Debt Investments Held [Abstract]
Future Funding Obligations	$ 231,924
Senior Financing	7,140,238
Carrying Value	1,969,618		1,592,537
Total fixed rate
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	3,616,476
Carrying Value	635,368		360,359
Total fixed rate | Mortgage and Jr Mortgage Loan with an Initial Maturity Date of April 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	250,464		0
Loan acquired	259,300
Total fixed rate | Junior Mortgage Participation, Related To Mortgage Loan, February 2019
Debt Investments Held [Abstract]
Loan acquired				$ 5,700
Discount amount				5,700
Total fixed rate | Mortgage Loan With An Initial Maturity Date Of February 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	26,366		26,311
Loan acquired				26,400
Discount amount				$ 200
Total fixed rate | Mortgage Loan with an Initial Maturity of August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	239		380
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,160,000
Carrying Value	204,005		0
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of September 2021
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	15,000
Carrying Value	3,500		3,500
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of April 2022
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	147,000
Carrying Value	24,913		0
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of November 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	86,976
Carrying Value	12,699		12,692
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of June 2024
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	115,000
Carrying Value	12,932		12,925
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of January 2025
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	95,000
Carrying Value	30,000		30,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of November 2026
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	340,000
Carrying Value	15,000		15,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of June 2027
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,657,500
Carrying Value	55,250		0
Total fixed rate | Mezzanine Loan Repaid in June 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0		66,129
Total fixed rate | Junior Mortgage Participation or Mezzanine Loan repaid in March 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0		193,422
Total floating rate
Debt Investments Held [Abstract]
Future Funding Obligations	231,924
Senior Financing	3,523,762
Carrying Value	1,334,250		1,232,178
Total floating rate | Mezzanine Loan with an Initial Maturity of March 2018
Debt Investments Held [Abstract]
Future Funding Obligations	795
Senior Financing	0
Carrying Value	15,148		15,051
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000
Carrying Value	19,982		19,913
Total floating rate | Junior Mortgage Participation Loan with an Initial Maturity Date of April 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	94,546
Carrying Value	34,947		34,844
Total floating rate | Mezzanine Loan with an Initial Maturity Date of August 2018
Debt Investments Held [Abstract]
Future Funding Obligations	523
Senior Financing	20,523
Carrying Value	10,934		10,863
Total floating rate | Mortgage/Mezzanine Loan, with an Initial Maturity Date of August 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	19,940		19,840
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of August 2018, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	65,000
Carrying Value	14,955		14,880
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of September 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	16,969		16,960
Total floating rate | Mezzanine Loan with an Initial Maturity Date of September 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	37,500
Carrying Value	14,855		14,648
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of October 2018
Debt Investments Held [Abstract]
Future Funding Obligations	391
Senior Financing	0
Carrying Value	23,609		20,423
Total floating rate | Mezzanine Loan with an Initial Maturity Date of October 2018
Debt Investments Held [Abstract]
Future Funding Obligations	2,325
Senior Financing	45,025
Carrying Value	34,879		34,502
Total floating rate | Mezzanine Loan with an Initial Maturity Date of November 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	335,000
Carrying Value	74,755		74,476
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	85,000
Carrying Value	15,381		15,141
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	65,000
Carrying Value	14,869		14,656
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 3
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	33,000
Carrying Value	26,927		26,850
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 4
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	175,000
Carrying Value	59,723		56,114
Total floating rate | Mezzanine Loan with an Initial Maturity Date of January 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	45,000
Carrying Value	12,174		12,104
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of January 2019
Debt Investments Held [Abstract]
Future Funding Obligations	26,284
Senior Financing	0
Carrying Value	162,553		0
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2019, 3
Debt Investments Held [Abstract]
Future Funding Obligations	5,372
Senior Financing	25,289
Carrying Value	8,550		5,410
Total floating rate | Mezzanine Loan with an Initial Maturity of March 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	38,000
Carrying Value	21,939		21,891
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2019
Debt Investments Held [Abstract]
Future Funding Obligations	11
Senior Financing	174,947
Carrying Value	37,250		0
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2019, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	265,000
Carrying Value	24,830		24,707
Total floating rate | Mortgage/Jr Mortgage Participate Loan, Maturity Date of August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	27,617
Senior Financing	199,733
Carrying Value	71,832		65,554
Total floating rate | Mezzanine Loan, Maturity of September 2019
Debt Investments Held [Abstract]
Future Funding Obligations	2,034
Senior Financing	189,829
Carrying Value	37,851		37,322
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of September 2019
Debt Investments Held [Abstract]
Future Funding Obligations	36,391
Senior Financing	0
Carrying Value	143,919		111,819
Total floating rate | Mezzanine Loan with an Initial Maturity of October 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	350,000
Carrying Value	34,737		0
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	25,643
Senior Financing	0
Carrying Value	43,845		33,682
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	3,621
Senior Financing	555,379
Carrying Value	75,834		125,911
Amount participated out	66,100
Total floating rate | Mezzanine Loan with an Initial Maturity of July 2020
Debt Investments Held [Abstract]
Future Funding Obligations	6,913
Senior Financing	34,337
Carrying Value	11,259		0
Total floating rate | Mezzanine Loan with an Initial Maturity of November 2020
Debt Investments Held [Abstract]
Future Funding Obligations	51,494
Senior Financing	310,654
Carrying Value	75,428		63,137
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of December 2020
Debt Investments Held [Abstract]
Future Funding Obligations	42,510
Senior Financing	0
Carrying Value	88,989		0
Total floating rate | Mortgage/Mezzanine Loan 2 with an Initial Maturity of December 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	35,152		0
Total floating rate | Jr Mortgage Participation/Mezzanine Loan with an Initial Maturity of July 2021
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	60,000
Carrying Value	15,635		15,606
Total floating rate | Mezzanine Loan With An Initial Maturity Of August 2022
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	280,000
Carrying Value	34,600		0
Total floating rate | Mortgage/Mezzanine Loan Repaid in December 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0		29,998
Total floating rate | Mezzanine Loan Repaid In November 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0		64,505
Total floating rate | Mezzanine Loan, repaid in September 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0		15,369
Total floating rate | Mortgage/Mezzanine Loan repaid in June 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0		32,847
Total floating rate | Mortgage/Mezzanine Loan repaid in June 2017, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0		22,959
Total floating rate | Mezzanine Loan Contributed To Joint Venture In May 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0		14,957
Total floating rate | Mortgage/Mezzanine Loan repaid in January 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	$ 0		$ 145,239

Debt and Preferred Equity Inv77

Debt and Preferred Equity Investments - Preferred Equity Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Preferred equity investment
Mortgage loans on real estate, interest rate	9.31%
Carrying Value	$ 2,114,041	$ 1,640,412
Preferred Equity, April 2021
Preferred equity investment
Future Funding Obligations	0
Senior Financing	272,000
Carrying Value	144,423	0
Preferred Equity Redeemed in May 2017
Preferred equity investment
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	9,982
Preferred Equity Redeemed in April 2017
Preferred equity investment
Future Funding Obligations	0
Senior Financing	0
Carrying Value	$ 0	37,893
Preferred equity investments
Preferred equity investment
Mortgage loans on real estate, interest rate	6.99%
Future Funding Obligations	$ 0
Senior Financing	272,000
Carrying Value	$ 144,423	$ 47,875

Debt and Preferred Equity Inv78

Debt and Preferred Equity Investments - Rollforward of Total Allowance for Loan Loss Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loan loss reserve activity
Balance at beginning of year	$ 0	$ 0	$ 0
Expensed	0	0	0
Recoveries	0	0	0
Charge-offs and reclassifications	0	0	0
Balance at end of year	$ 0	$ 0	$ 0

Debt and Preferred Equity Inv79

Debt and Preferred Equity Investments - Narrative (Details)	1 Months Ended	12 Months Ended
	Sep. 30, 2014USD ($)	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)segment
Preferred equity investment
Carrying Value		$ 2,114,041,000	$ 1,640,412,000
Number of portfolio segments of financial receivables (segment) | segment		1	1
Additional amount of financing receivables included in other assets		$ 65,500,000	$ 99,500,000
Junior Mortgage Participation Acquired in September 2014
Preferred equity investment
Payments to acquire loans receivable	$ 0
Carrying Value		$ 0

Investments in Unconsolidated80

Investments in Unconsolidated Joint Ventures - Additional Information (Details) $ in Thousands	1 Months Ended						3 Months Ended	12 Months Ended
	Feb. 22, 2018	Nov. 30, 2017	Oct. 31, 2017	May 31, 2017USD ($)	Oct. 31, 2016ft²	Aug. 31, 2016ft²	Dec. 31, 2017USD ($)ft²unit	Dec. 31, 2017USD ($)ft²unit	Sep. 30, 2017USD ($)	Jan. 31, 2017partner	Dec. 31, 2016USD ($)
General information on each joint venture
Net equity investment in VIEs							$ 606,200	$ 606,200			$ 220,100
Approximate Square Feet (sqft) | ft²							33,253,213	33,253,213
11 Madison Avenue
General information on each joint venture
Approximate Square Feet (sqft) | ft²						2,314,000
Ownership percentage in disposed asset						40.00%
400 East 57th Street
General information on each joint venture
Approximate Square Feet (sqft) | ft²					290,482
Ownership percentage in disposed asset					49.00%
100 Park Avenue
General information on each joint venture
Ownership Interest							49.90%	49.90%
Economic Interest, percent							49.90%	49.90%
Approximate Square Feet (sqft) | ft²							834,000	834,000
Acquisition Price							$ 95,800	$ 95,800
717 Fifth Avenue
General information on each joint venture
Ownership Interest							10.92%	10.92%
Approximate Square Feet (sqft) | ft²							119,500	119,500
Acquisition Price							$ 251,900	$ 251,900
800 Third Avenue
General information on each joint venture
Ownership Interest							60.52%	60.52%
Economic Interest, percent							60.52%	60.52%
Approximate Square Feet (sqft) | ft²							526,000	526,000
Acquisition Price							$ 285,000	$ 285,000
1745 Broadway
General information on each joint venture
Ownership Interest							56.87%	56.87%
Economic Interest, percent							56.87%	56.87%
Approximate Square Feet (sqft) | ft²							674,000	674,000
Acquisition Price							$ 520,000	$ 520,000
Jericho Plaza
General information on each joint venture
Ownership Interest							11.67%	11.67%
Economic Interest, percent							11.67%	11.67%
Approximate Square Feet (sqft) | ft²							640,000	640,000
Acquisition Price							$ 210,000	$ 210,000
Investment in joint venture, investment expense							$ 6,600
11 West 34th Street
General information on each joint venture
Ownership Interest							30.00%	30.00%
Economic Interest, percent							30.00%	30.00%
Approximate Square Feet (sqft) | ft²							17,150	17,150
Acquisition Price							$ 10,800	$ 10,800
3 Columbus Circle
General information on each joint venture
Ownership Interest							48.90%	48.90%
Economic Interest, percent							48.90%	48.90%
Approximate Square Feet (sqft) | ft²							741,500	741,500
Acquisition Price							$ 500,000	$ 500,000
280 Park Avenue
General information on each joint venture
Ownership Interest							50.00%	50.00%
Economic Interest, percent							50.00%	50.00%
Approximate Square Feet (sqft) | ft²							1,219,158	1,219,158
Acquisition Price							$ 400,000	$ 400,000
1552-1560 Broadway
General information on each joint venture
Ownership Interest							50.00%	50.00%
Economic Interest, percent							50.00%	50.00%
Approximate Square Feet (sqft) | ft²							57,718	57,718
Acquisition Price							$ 136,550	$ 136,550
724 Fifth Avenue
General information on each joint venture
Ownership Interest							50.00%	50.00%
Economic Interest, percent							50.00%	50.00%
Approximate Square Feet (sqft) | ft²							65,010	65,010
Acquisition Price							$ 223,000	$ 223,000
10 East 53rd Street
General information on each joint venture
Ownership Interest							55.00%	55.00%
Economic Interest, percent							55.00%	55.00%
Approximate Square Feet (sqft) | ft²							354,300	354,300
Acquisition Price							$ 252,500	$ 252,500
521 Fifth Avenue
General information on each joint venture
Ownership Interest							50.50%	50.50%
Economic Interest, percent							50.50%	50.50%
Approximate Square Feet (sqft) | ft²							460,000	460,000
Acquisition Price							$ 315,000	$ 315,000
21 East 66th Street
General information on each joint venture
Ownership Interest							32.28%	32.28%
Economic Interest, percent							32.28%	32.28%
Approximate Square Feet (sqft) | ft²							13,069	13,069
Acquisition Price							$ 75,000	$ 75,000
21 East 66th Street | Three Retail and Two Residential Units
General information on each joint venture
Ownership Interest							32.28%	32.28%
Number of Stores | unit							3	3
Number of residential units | unit							2	2
21 East 66th Street | Three Residential Units
General information on each joint venture
Ownership Interest							16.14%	16.14%
Number of residential units | unit							3	3
650 Fifth Avenue
General information on each joint venture
Ownership Interest							50.00%	50.00%
Approximate Square Feet (sqft) | ft²							69,214	69,214
Acquisition Price							$ 0	$ 0
121 Greene Street
General information on each joint venture
Ownership Interest							50.00%	50.00%
Economic Interest, percent							50.00%	50.00%
Approximate Square Feet (sqft) | ft²							7,131	7,131
Acquisition Price							$ 27,400	$ 27,400
175-225 Third Street Brooklyn, New York
General information on each joint venture
Ownership Interest							95.00%	95.00%
Economic Interest, percent							95.00%	95.00%
Approximate Square Feet (sqft) | ft²							0	0
Acquisition Price							$ 74,600	$ 74,600
55 West 46th Street
General information on each joint venture
Ownership Interest							25.00%	25.00%
Economic Interest, percent							25.00%	25.00%
Approximate Square Feet (sqft) | ft²							347,000	347,000
Acquisition Price							$ 295,000	$ 295,000
Stonehenge Portfolio
General information on each joint venture
Ownership Interest					90.00%
Approximate Square Feet (sqft) | ft²							1,439,016	1,439,016
Acquisition Price							$ 36,668	$ 36,668
131-137 Spring Street
General information on each joint venture
Ownership Interest							20.00%	20.00%
Economic Interest, percent							20.00%	20.00%
Approximate Square Feet (sqft) | ft²							68,342	68,342
Acquisition Price							$ 277,750	$ 277,750
605 West 42nd Street
General information on each joint venture
Ownership Interest							20.00%	20.00%
Economic Interest, percent							20.00%	20.00%
Approximate Square Feet (sqft) | ft²							927,358	927,358
Acquisition Price							$ 759,000	$ 759,000
11 Madison Avenue
General information on each joint venture
Ownership Interest							60.00%	60.00%
Economic Interest, percent							60.00%	60.00%
Approximate Square Feet (sqft) | ft²							2,314,000	2,314,000
Acquisition Price							$ 2,605,000	$ 2,605,000
333 East 22nd St
General information on each joint venture
Ownership Interest							33.33%	33.33%
Economic Interest, percent							33.33%	33.33%
Approximate Square Feet (sqft) | ft²							26,926	26,926
Acquisition Price							$ 0	$ 0
400 East 57th Street
General information on each joint venture
Ownership Interest							51.00%	51.00%
Economic Interest, percent							41.00%	41.00%
Approximate Square Feet (sqft) | ft²							290,482	290,482
Acquisition Price							$ 170,000	$ 170,000
One Vanderbilt
General information on each joint venture
Ownership Interest							71.01%	71.01%
Economic Interest, percent							71.01%	71.01%
Approximate Square Feet (sqft) | ft²							0	0
Acquisition Price							$ 3,310,000	$ 3,310,000
Number of joint venture partners | partner										2
Investment in joint venture, aggregate equity committed by partner									$ 525,000
Investment in joint venture, aggregate maximum ownership percentage									29.00%
Investment in joint venture, partners' ownership percentage									3.48%
Worldwide Plaza
General information on each joint venture
Ownership Interest							24.35%	24.35%
Economic Interest, percent							24.35%	24.35%
Approximate Square Feet (sqft) | ft²							2,048,725	2,048,725
Acquisition Price							$ 1,725,000	$ 1,725,000
1515 Broadway
General information on each joint venture
Ownership Interest							69.87%	69.87%
Economic Interest, percent							69.87%	69.87%
Approximate Square Feet (sqft) | ft²							1,750,000	1,750,000
Acquisition Price							$ 1,950,000	$ 1,950,000
Equity method investments, depreciation								$ 900
1552 Broadway
General information on each joint venture
Approximate Square Feet (sqft) | ft²							13,045	13,045
Joint venture | Stonehenge Portfolio
General information on each joint venture
Ownership Interest					10.00%
Mezzanine Loan Contributed To Joint Venture In May 2017
General information on each joint venture
Ownership Interest				33.33%			33.33%	33.33%
Economic Interest, percent							33.33%	33.33%
Approximate Square Feet (sqft) | ft²							0	0
Acquisition Price							$ 15,000	$ 15,000
Equity method investment, amount sold				$ 10,000
RXR Realty | Joint venture | Worldwide Plaza
General information on each joint venture
Ownership Interest			50.00%
Ownership interest acquired (percent)			48.70%
New York REIT | Worldwide Plaza
General information on each joint venture
Ownership Interest			51.30%
Allianz Real Estate | 1515 Broadway
General information on each joint venture
Ownership percentage in disposed asset		30.13%
Subsequent Event | Allianz Real Estate | 1515 Broadway
General information on each joint venture
Ownership percentage in disposed asset	12.87%

Investments in Unconsolidated81

Investments in Unconsolidated Joint Ventures - Acquisition, Development and Construction Arrangements/Sale of Joint Venture Interest or Property (Details) $ in Thousands	1 Months Ended							3 Months Ended								9 Months Ended	12 Months Ended
	May 31, 2017USD ($)note	Sep. 30, 2016USD ($)	May 31, 2016USD ($)	Mar. 31, 2016USD ($)	Feb. 29, 2016USD ($)	Sep. 30, 2015USD ($)	Aug. 31, 2015USD ($)	Dec. 31, 2017USD ($)ft²	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)ft²	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Apr. 30, 2017USD ($)ft²
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures								$ 2,362,989				$ 1,890,186					$ 2,362,989	$ 1,890,186
Acquisition, development and construction arrangements, carrying value								171,539				170,164					171,539	170,164
Gain (Loss) on Sale								0	$ 1,030	$ 13,089	$ 2,047	421	$ 225	$ 33,448	$ 9,915		16,166	44,009	$ 15,844
Employee compensation award								$ 900		2,500							$ 0	1,100	1,200
Approximate Square Feet (sqft) | ft²								33,253,213									33,253,213
Gain on sale of real estate, net								$ 76,497	$ 0	$ (3,823)	$ 567	27,366	$ 397	$ 196,580	$ 13,773		$ 73,241	238,116	$ 175,974
76 11th Avenue
Schedule of Equity Method Investments [Line Items]
Number of notes owned | note	2
Participating Financing Due March 2017
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures								100,000				100,000					100,000	100,000
Participating Financing Due February 2022
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures								44,823				45,622					44,823	45,622
Mezzanine Loan Due July 2036
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures								$ 26,716				$ 24,542					$ 26,716	$ 24,542
747 Madison Avenue
Schedule of Equity Method Investments [Line Items]
Gain on sale of real estate, net	$ 13,000
102 Greene Street
Schedule of Equity Method Investments [Line Items]
Ownership Interest									10.00%							10.00%
Gross asset valuation									$ 43,500							$ 43,500				$ 43,500
Gain (Loss) on Sale																$ 283
Approximate Square Feet (sqft) | ft²																				9,200
Stonehenge Portfolio
Schedule of Equity Method Investments [Line Items]
Gross asset valuation	300,000
Gain (Loss) on Sale	$ 871
EOP Denver
Schedule of Equity Method Investments [Line Items]
Ownership Interest									0.48%							0.48%
Gross asset valuation									$ 180,700							$ 180,700
Gain (Loss) on Sale		$ 300
33 Beekman
Schedule of Equity Method Investments [Line Items]
Ownership Interest			45.90%
Gross asset valuation			$ 196,000
Gain (Loss) on Sale			33,000
Promote recognized			$ 10,800
EOP Denver
Schedule of Equity Method Investments [Line Items]
Ownership Interest											4.79%
Gross asset valuation											$ 180,700
Gain (Loss) on Sale				$ 2,800
7 Renaissance
Schedule of Equity Method Investments [Line Items]
Ownership Interest											50.00%
Gross asset valuation											$ 20,700
Gain (Loss) on Sale				$ 4,200
1 Jericho
Schedule of Equity Method Investments [Line Items]
Ownership Interest				11.67%	66.11%										11.67%				77.78%
Gross asset valuation					$ 95,200
Gain (Loss) on Sale					$ 3,300
The Meadows
Schedule of Equity Method Investments [Line Items]
Ownership Interest							50.00%
Gross asset valuation							$ 121,100
Gain (Loss) on Sale							$ (1,600)
315 West 36th Street
Schedule of Equity Method Investments [Line Items]
Ownership Interest		35.50%											35.50%
Gross asset valuation		$ 115,000											$ 115,000
Gain (Loss) on Sale						$ 16,300

Investments in Unconsolidated82

Investments in Unconsolidated Joint Ventures - Mortgages and Other Loans Payable (Details)	12 Months Ended
	Dec. 31, 2017USD ($)extenstion_option	Jan. 31, 2018USD ($)	Nov. 30, 2017USD ($)	Nov. 29, 2017USD ($)	Dec. 31, 2016USD ($)	Oct. 31, 2016
Debt Instrument [Line Items]
Long-term debt	$ 2,837,282,000				$ 4,073,830,000
Total fixed rate debt	2,400,560,000				3,518,127,000
Total floating rate debt	465,431,000				622,585,000
Total fixed rate and floating rate debt	2,865,991,000				4,140,712,000
Deferred financing costs, net	$ (28,709,000)				(66,882,000)
Number of extension options | extenstion_option	2
Debt Instrument, period of extension option	1 year
1745 Broadway
Debt Instrument [Line Items]
Economic Interest, percent	56.87%
Ownership Interest	56.87%
521 Fifth Avenue
Debt Instrument [Line Items]
Economic Interest, percent	50.50%
Ownership Interest	50.50%
717 Fifth Avenue
Debt Instrument [Line Items]
Ownership Interest	10.92%
717 Fifth Avenue | Mezzanine loans
Debt Instrument [Line Items]
Economic Interest, percent	10.92%
21 East 66th Street
Debt Instrument [Line Items]
Economic Interest, percent	32.28%
Ownership Interest	32.28%
3 Columbus Circle
Debt Instrument [Line Items]
Economic Interest, percent	48.90%
Ownership Interest	48.90%
1515 Broadway
Debt Instrument [Line Items]
Economic Interest, percent	69.87%
Total fixed rate debt	$ 0				888,531,000
Ownership Interest	69.87%
11 Madison Avenue
Debt Instrument [Line Items]
Economic Interest, percent	60.00%
Ownership Interest	60.00%
800 Third Avenue
Debt Instrument [Line Items]
Economic Interest, percent	60.52%
Ownership Interest	60.52%
400 East 57th Street
Debt Instrument [Line Items]
Economic Interest, percent	41.00%
Ownership Interest	51.00%
Worldwide Plaza
Debt Instrument [Line Items]
Economic Interest, percent	24.35%
Ownership Interest	24.35%
Stonehenge Portfolio
Debt Instrument [Line Items]
Ownership Interest						90.00%
Jericho Plaza
Debt Instrument [Line Items]
Economic Interest, percent	11.67%
Ownership Interest	11.67%
280 Park Avenue
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Ownership Interest	50.00%
10 East 53rd Street
Debt Instrument [Line Items]
Economic Interest, percent	55.00%
Ownership Interest	55.00%
724 Fifth Avenue
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Ownership Interest	50.00%
55 West 46th Street
Debt Instrument [Line Items]
Economic Interest, percent	25.00%
Ownership Interest	25.00%
175-225 Third Street Brooklyn, New York
Debt Instrument [Line Items]
Economic Interest, percent	95.00%
Ownership Interest	95.00%
605 West 42nd Street
Debt Instrument [Line Items]
Economic Interest, percent	20.00%
Ownership Interest	20.00%
650 Fifth Avenue
Debt Instrument [Line Items]
Ownership Interest	50.00%
650 Fifth Avenue | Mortgage loan
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
121 Greene Street
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Ownership Interest	50.00%
131-137 Spring Street
Debt Instrument [Line Items]
Economic Interest, percent	20.00%
Ownership Interest	20.00%
1552-1560 Broadway
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Ownership Interest	50.00%
11 West 34th Street
Debt Instrument [Line Items]
Economic Interest, percent	30.00%
Ownership Interest	30.00%
100 Park Avenue
Debt Instrument [Line Items]
Economic Interest, percent	49.90%
Ownership Interest	49.90%
One Vanderbilt
Debt Instrument [Line Items]
Economic Interest, percent	71.01%
Total floating rate debt	$ 0				64,030,000
Ownership Interest	71.01%
Joint venture
Debt Instrument [Line Items]
Total fixed rate debt	$ 5,569,138,000				3,566,846,000
Total floating rate debt	3,979,066,000				2,982,528,000
Total fixed rate and floating rate debt	9,548,204,000				6,549,374,000
Deferred financing costs, net	(136,103,000)				(95,408,000)
Total joint venture mortgages and other loans payable, net	$ 9,412,101,000				6,453,966,000
Joint venture | 1745 Broadway
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.85%
Total fixed rate debt	$ 0				340,000,000
Total floating rate debt	345,000,000				0
Committed amount	375,000,000
Unused borrowing capacity, amount	$ 30,000,000
Joint venture | 521 Fifth Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.73%
Total fixed rate debt	$ 170,000,000				170,000,000
Joint venture | 717 Fifth Avenue | Mortgage loan
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.45%
Total fixed rate debt	$ 300,000,000				300,000,000
Committed amount	$ 300,000,000
Joint venture | 717 Fifth Avenue | Mezzanine loans
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.50%
Total fixed rate debt	$ 355,328,000				355,328,000
Committed amount	$ 355,300,000
Joint venture | 21 East 66th Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.60%
Total fixed rate debt	$ 12,000,000				12,000,000
Total floating rate debt	$ 1,648,000				1,726,000
Joint venture | 3 Columbus Circle
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.61%
Total fixed rate debt	$ 350,000,000				350,000,000
Joint venture | 1515 Broadway
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.93%
Total fixed rate debt	$ 872,528,000				0
Joint venture | 11 Madison Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.84%
Total fixed rate debt	$ 1,400,000,000				1,400,000,000
Joint venture | 800 Third Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.37%
Total fixed rate debt	$ 177,000,000				177,000,000
Joint venture | 400 East 57th Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.00%
Total fixed rate debt	$ 100,000,000				100,000,000
Joint venture | Worldwide Plaza
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.98%
Total fixed rate debt	$ 1,200,000,000				0
Joint venture | Stonehenge Portfolio
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.17%
Total fixed rate debt	$ 357,282,000				362,518,000
Total floating rate debt	55,340,000				65,577,000
Ownership Interest						10.00%
Joint venture | Stonehenge Portfolio | Initial Maturity August 2019
Debt Instrument [Line Items]
Total fixed rate debt	137,100,000
Joint venture | Stonehenge Portfolio | Initial Maturity June 2024
Debt Instrument [Line Items]
Total fixed rate debt	171,600,000
Joint venture | Stonehenge Portfolio | Secured Debt, Initial Maturity January 2018
Debt Instrument [Line Items]
Total fixed rate debt	33,800,000
Joint venture | Stonehenge Portfolio | Secured Debt, Initial Maturity February 2027
Debt Instrument [Line Items]
Total fixed rate debt	14,800,000
Joint venture | Jericho Plaza
Debt Instrument [Line Items]
Total floating rate debt	$ 81,100,000
Initial Term (in Years)	2 years
Face amount of loan	$ 100,000,000
Joint venture | 280 Park Avenue
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.73%
Total floating rate debt	$ 1,200,000,000				900,000,000
Joint venture | 10 East 53rd Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.25%
Total floating rate debt	$ 170,000,000				125,000,000
Joint venture | 724 Fifth Avenue
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.42%
Total floating rate debt	$ 275,000,000				275,000,000
Joint venture | 55 West 46th Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.13%
Total floating rate debt	$ 171,444,000				157,322,000
Committed amount	195,000,000
Unused borrowing capacity, amount	$ 23,600,000
Joint venture | 175-225 Third Street Brooklyn, New York
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.00%
Total floating rate debt	$ 40,000,000				40,000,000
Joint venture | Jericho Plaza
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	4.15%
Total floating rate debt	$ 81,099,000				76,993,000
Joint venture | 605 West 42nd Street
Debt Instrument [Line Items]
Total floating rate debt	550,000,000				539,000,000
Joint venture | 650 Fifth Avenue
Debt Instrument [Line Items]
Total floating rate debt	$ 0				77,500,000
Joint venture | 650 Fifth Avenue | Mortgage loan
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.46%		4.46%
Long-term debt			$ 210,000,000	$ 225,000,000
Total fixed rate debt	$ 210,000,000				0
Joint venture | 650 Fifth Avenue | Mezzanine loans
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.45%
Total fixed rate debt	$ 65,000,000				0
Joint venture | 650 Fifth Avenue | Mezzanine Loan, Initial Maturity October 2022 | Mezzanine loans
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)			5.45%
Long-term debt			$ 65,000,000
Face amount of loan			$ 65,000,000
Joint venture | 121 Greene Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.50%
Total floating rate debt	$ 15,000,000				15,000,000
Joint venture | 131-137 Spring Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.55%
Total floating rate debt	$ 141,000,000				141,000,000
Joint venture | 1552-1560 Broadway
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.65%
Total floating rate debt	$ 195,000,000				185,410,000
Joint venture | 11 West 34th Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.45%
Total floating rate debt	$ 23,000,000				23,000,000
Joint venture | 100 Park Avenue
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.75%
Total floating rate debt	$ 360,000,000				360,000,000
Joint venture | One Vanderbilt
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	3.50%
Total floating rate debt	$ 355,535,000				$ 0
Joint venture | One Vanderbilt | Line of Credit
Debt Instrument [Line Items]
Long-term debt	$ 1,500,000,000
Initial Term (in Years)	5 years
Number of extension options	2
Debt Instrument, period of extension option	1 year
Joint venture | Weighted Average | 21 East 66th Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.75%
Joint venture | Weighted Average | Stonehenge Portfolio
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.25%
Joint venture | Weighted Average | 605 West 42nd Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.44%
Joint venture | LIBOR | One Vanderbilt | Line of Credit
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.50%
Joint venture | LIBOR | Subsequent Event | Stonehenge Portfolio | Mortgage Loan, Initial Maturity January 2021 | Mortgage loan
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)		1.40%
Face amount of loan		$ 38,000,000

Investments in Unconsolidated83

Investments in Unconsolidated Joint Ventures - Schedules of Combined Financial Statements for the Unconsolidated Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Commercial real estate property, net	$ 7,906,006				$ 10,478,638				$ 7,906,006	$ 10,478,638
Cash and cash equivalents	127,888				279,443				127,888	279,443	$ 255,399	$ 281,409
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	57,644				53,772				57,644	53,772
Carrying Value	2,114,041				1,640,412				2,114,041	1,640,412
Other assets	310,688				614,067				310,688	614,067
Liabilities and members' equity
Mortgages and other loans payable, net	2,837,282				4,073,830				2,837,282	4,073,830
Deferred revenue	208,119				217,955				208,119	217,955
Other liabilities	188,005				206,238				188,005	206,238
Company's investments in unconsolidated joint ventures	2,362,989				1,890,186				2,362,989	1,890,186
Combined statements of income for the unconsolidated joint ventures
Ground rent									33,231	33,261	32,834
Real estate taxes									244,323	248,388	232,702
Interest expense, net of interest income									257,045	321,199	323,870
Amortization of deferred financing costs									16,498	24,564	27,348
Transaction related costs									(1,834)	7,528	11,430
Depreciation and amortization									403,320	821,041	560,887
Total expenses									1,346,445	1,868,599	1,585,568
Company's equity in net income from unconsolidated joint ventures	7,788	$ 4,078	$ 3,412	$ 6,614	(95)	$ (3,968)	$ 5,841	$ 10,096	21,892	11,874	13,028
Joint venture
Investment in Unconsolidated Joint Ventures
Management fees, base revenue									22,600	4,000	3,400
Assets
Commercial real estate property, net	12,822,133				9,131,717				12,822,133	9,131,717
Cash and cash equivalents	494,909				328,455				494,909	328,455
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	349,944				232,778				349,944	232,778
Carrying Value	202,539				336,164				202,539	336,164
Other assets	1,407,806				683,481				1,407,806	683,481
Total assets	15,277,331				10,712,595				15,277,331	10,712,595
Liabilities and members' equity
Mortgages and other loans payable, net	9,412,101				6,453,966				9,412,101	6,453,966
Deferred revenue	985,648				356,414				985,648	356,414
Other liabilities	411,053				391,500				411,053	391,500
Members' equity	4,468,529				3,510,715				4,468,529	3,510,715
Total liabilities and members' equity	$ 15,277,331				$ 10,712,595				15,277,331	10,712,595
Combined statements of income for the unconsolidated joint ventures
Total revenues									904,230	712,689	576,845
Operating expenses									157,610	126,913	106,613
Ground rent									16,794	14,924	14,083
Real estate taxes									142,774	111,673	89,734
Interest expense, net of interest income									250,063	197,741	199,126
Amortization of deferred financing costs									23,026	24,829	13,394
Transaction related costs									146	5,566	615
Depreciation and amortization									279,419	199,011	149,023
Total expenses									869,832	680,657	572,588
Loss on early extinguishment of debt									(7,899)	(1,606)	(1,089)
Net income before gain on sale									26,499	30,426	3,168
Company's equity in net income from unconsolidated joint ventures									$ 21,892	$ 11,874	$ 13,028

Deferred Costs (Details)

Deferred Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred leasing costs	$ 443,341	$ 468,971
Less: accumulated amortization	(217,140)	(201,371)
Deferred costs, net	$ 226,201	$ 267,600

Mortgages and Other Loans Pay85

Mortgages and Other Loans Payable (Details)	1 Months Ended			12 Months Ended
	Feb. 22, 2018	Jan. 31, 2018	Nov. 30, 2017	Dec. 31, 2017USD ($)extenstion_optiondebt_instrument$ / shares	Jun. 30, 2017USD ($)	Jan. 31, 2017partner	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jul. 31, 2016USD ($)
Debt Instrument [Line Items]
Total fixed rate debt				$ 2,400,560,000			$ 3,518,127,000
Total floating rate debt				465,431,000			622,585,000
Total fixed rate and floating rate debt				2,865,991,000			4,140,712,000
Mortgages reclassed to liabilities related to assets held for sale				0			0
Total mortgages and other loans payable				2,865,991,000			4,140,712,000
Total mortgages and other loans payable				$ 2,837,282,000			4,073,830,000
Number of extension options | extenstion_option				2
Debt Instrument, period of extension option				1 year
Revolving credit facility, net				$ 30,336,000			0
Deferred financing costs, net				28,709,000			66,882,000
Collateral already posted, aggregate fair value				4,800,000,000			6,000,000,000
Series J Preferred Units
Debt Instrument [Line Items]
Total fixed rate debt				4,000,000			4,000,000
Temporary equity, carrying amount, attributable to noncontrolling interest				$ 4,000,000
Preferred Units (as a percent)				3.75%
Preferred Units, liquidation preference (in dollars per unit) | $ / shares				$ 1,000
Series J Preferred Units | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				3.75%
FHLB Advance Maturing in January 2017
Debt Instrument [Line Items]
Total fixed rate debt				$ 0			105,000,000
FHLB Advance Maturing in January 2017, 2
Debt Instrument [Line Items]
Total fixed rate debt				0			100,000,000
Uncommitted Master Repurchase Agreement 2017
Debt Instrument [Line Items]
Total floating rate debt				$ 90,809,000			0
Initial Term (in Years)				1 year
Maximum facility capacity					$ 300,000,000
Revolving credit facility, net				$ 90,100,000
Uncommitted Master Repurchase Agreement 2017 | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)				2.38%
Unsecured Debt
Debt Instrument [Line Items]
Total fixed rate debt				$ 16,000,000			16,000,000
Unsecured Debt | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				4.81%
Master Repurchase Agreement
Debt Instrument [Line Items]
Total floating rate debt				$ 0			184,642,000
Initial Term (in Years)				2 years
Maximum facility capacity									$ 300,000,000
Debt Instrument, period of extension option				1 year
Revolving credit facility, net				$ (1,200,000)
Basis Point Fee (as a percent)				0.25%
Threshold amount for basis point fee to be applicable (less than)				$ 150,000,000
Master Repurchase Agreement | Minimum | LIBOR
Debt Instrument [Line Items]
Credit facility, interest rate (as a percent)				2.25%
Master Repurchase Agreement | Maximum | LIBOR
Debt Instrument [Line Items]
Credit facility, interest rate (as a percent)				4.00%
Uncommitted Master Repurchase Agreements
Debt Instrument [Line Items]
Debt instrument, number of instruments | debt_instrument				2
485 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt				$ 450,000,000			450,000,000
485 Lexington Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				4.25%
762 Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt				$ 771,000			7,694,000
762 Madison Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				5.00%
One Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt				$ 486,153,000			517,806,000
One Madison Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				5.91%
100 Church Street
Debt Instrument [Line Items]
Total fixed rate debt				$ 217,273,000			221,446,000
100 Church Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				4.68%
919 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt				$ 500,000,000			500,000,000
Interest in property (as a percent)				51.00%
919 Third Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				5.12%
420 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt				$ 300,000,000			300,000,000
420 Lexington Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				3.99%
1515 Broadway
Debt Instrument [Line Items]
Total fixed rate debt				$ 0			888,531,000
400 East 58th Street
Debt Instrument [Line Items]
Total fixed rate debt				$ 40,000,000			40,000,000
400 East 58th Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				3.00%
Initial Term (in Years)				5 years
Landmark Square
Debt Instrument [Line Items]
Total fixed rate debt				$ 100,000,000			100,000,000
Landmark Square | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				4.90%
885 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt				$ 0			267,650,000
885 Third Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)
719 Seventh Avenue
Debt Instrument [Line Items]
Total floating rate debt				$ 41,622,000			37,388,000
719 Seventh Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)				3.05%
183, 187 Broadway & 5-7 Dey Street
Debt Instrument [Line Items]
Total floating rate debt				$ 58,000,000			58,000,000
183, 187 Broadway & 5-7 Dey Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)				2.70%
1080 Amsterdam
Debt Instrument [Line Items]
Total fixed rate debt				$ 36,363,000			0
Total floating rate debt				0			3,525,000
Secured debt, bearing fixed interest, mortgage amount				35,500,000
Secured debt, bearing fixed interest, subordinate loan amount				$ 900,000
1080 Amsterdam | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				3.58%
Initial Term (in Years)				5 years
1080 Amsterdam | Mortgage loan | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				3.50%
1080 Amsterdam | Senior Subordinated Loans | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				7.00%
315 West 33rd Street
Debt Instrument [Line Items]
Total fixed rate debt				$ 250,000,000			0
315 West 33rd Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)				4.17%
220 East 42nd Street
Debt Instrument [Line Items]
Total floating rate debt				$ 275,000,000			275,000,000
220 East 42nd Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)				1.60%
One Vanderbilt
Debt Instrument [Line Items]
Total floating rate debt				$ 0			$ 64,030,000
Number of joint venture partners | partner						2
One Vanderbilt | Construction Loans
Debt Instrument [Line Items]
Maximum facility capacity								$ 1,500,000,000
Number of joint venture partners | partner						2
Subsequent Event | 719 Seventh Avenue
Debt Instrument [Line Items]
Debt Instrument, period of extension option		1 year
Allianz Real Estate | 1515 Broadway
Debt Instrument [Line Items]
Ownership percentage in disposed asset			30.13%
Allianz Real Estate | Subsequent Event | 1515 Broadway
Debt Instrument [Line Items]
Ownership percentage in disposed asset	12.87%

Corporate Indebtedness - Additi

Corporate Indebtedness - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017USD ($)extension	Sep. 30, 2017USD ($)	Dec. 31, 2016USD ($)
Corporate Indebtedness
Outstanding under line of credit facility	$ 30,336,000		$ 0
Long-term debt	$ 2,837,282,000		4,073,830,000
Revolving credit facility
Corporate Indebtedness
Facility fee (as a percent)	0.20%
Outstanding under line of credit facility		$ 40,000,000
Revolving credit facility | Minimum
Corporate Indebtedness
Facility fee (as a percent)	0.125%
Revolving credit facility | Maximum
Corporate Indebtedness
Facility fee (as a percent)	0.30%
2012 Credit Facility
Corporate Indebtedness
Credit facility, maximum borrowing capacity	$ 1,500,000,000
Letters of credit	11,800,000
Ability to borrow under line of credit facility	1,400,000,000
Line of Credit | Revolving credit facility
Corporate Indebtedness
Long-term debt	30,300,000		(6,300,000)
Line of Credit | Term loan
Corporate Indebtedness
Long-term debt	1,500,000,000		$ 1,200,000,000
Term loan | Term Loan A, Maturity March 31, 2023
Corporate Indebtedness
Credit facility, maximum borrowing capacity	$ 1,300,000,000
Term loan | Term Loan A, Maturity March 31, 2023 | LIBOR
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.10%
Term loan | Term Loan A, Maturity March 31, 2023 | LIBOR | Minimum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	0.90%
Term loan | Term Loan A, Maturity March 31, 2023 | LIBOR | Maximum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.75%
Term loan | Term Loan B, Maturity November 21, 2024
Corporate Indebtedness
Credit facility, maximum borrowing capacity	$ 200,000,000
Term loan | Term Loan B, Maturity November 21, 2024 | LIBOR
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.65%
Term loan | Term Loan B, Maturity November 21, 2024 | LIBOR | Minimum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.50%
Term loan | Term Loan B, Maturity November 21, 2024 | LIBOR | Maximum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	2.45%
Revolving credit facility | Line of Credit | Revolving Credit Facility, Maturity March 31, 2022
Corporate Indebtedness
Credit facility, maximum borrowing capacity	$ 1,500,000,000
Number of extensions | extension	2
Term of extension	6 months
Maximum borrowing capacity, optional expansion	$ 4,500,000,000
Revolving credit facility | Line of Credit | Revolving Credit Facility, Maturity March 31, 2022 | LIBOR
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.00%
Revolving credit facility | Line of Credit | Revolving Credit Facility, Maturity March 31, 2022 | LIBOR | Minimum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	0.825%
Revolving credit facility | Line of Credit | Revolving Credit Facility, Maturity March 31, 2022 | LIBOR | Maximum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	1.55%

Corporate Indebtedness - Senior

Corporate Indebtedness - Senior Unsecured Notes (Details) - USD ($)	1 Months Ended	12 Months Ended
	Oct. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 5,905,991,000
Accreted Balance		1,395,939,000	$ 1,128,315,000
Deferred financing costs, net		(28,709,000)	(66,882,000)
Senior Unsecured Bonds | 4.50 Percent Senior Unsecured Bonds Due December 2022
Debt disclosures by scheduled maturity date
Coupon Rate (as a percent)	4.50%
Face amount of loan	$ 100,000,000
Redemption price, percentage	105.334%
Senior unsecured notes
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		1,400,000,000
Accreted Balance		1,404,605,000	1,133,957,000
Deferred financing costs, net		(8,666,000)	(5,642,000)
Senior Notes, Net of Deferred Finance Costs		1,395,939,000	1,128,315,000
Senior unsecured notes | 3.00% Senior unsecured notes maturing on October 15, 2017
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		0
Accreted Balance		0	334,077,000
Repayments of debt	$ 350,800,000
Senior unsecured notes | 5.00% Senior unsecured notes maturing on August 15, 2018
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		250,000,000
Accreted Balance		$ 249,953,000	249,880,000
Coupon Rate (as a percent)		5.00%
Initial Term (in Years)		7 years
Senior unsecured notes | 7.75% Senior unsecured notes maturing on March 15, 2020
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 250,000,000
Accreted Balance		$ 250,000,000	250,000,000
Coupon Rate (as a percent)		7.75%
Initial Term (in Years)		10 years
Senior unsecured notes | 3.25 Percent Senior Unsecured Notes Due October 2022 [Member]
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 500,000,000
Accreted Balance		$ 499,489,000	0
Coupon Rate (as a percent)		3.25%
Initial Term (in Years)		5 years
Senior unsecured notes | 4.50% Senior unsecured notes maturing on December 1, 2022
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 300,000,000
Accreted Balance		$ 305,163,000	200,000,000
Coupon Rate (as a percent)		4.50%
Initial Term (in Years)		10 years
Senior unsecured notes | 4.27% Senior unsecured notes maturing on December 17, 2025
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 100,000,000
Accreted Balance		$ 100,000,000	$ 100,000,000
Coupon Rate (as a percent)		4.27%
Initial Term (in Years)		10 years

Corporate Indebtedness - Junior

Corporate Indebtedness - Junior Subordinated Deferrable Interest Debentures and Principal Maturities (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2005	Dec. 31, 2017
Principal Repayments and Joint Venture Debt
2,018		$ 494,402,000
2,018		42,289,000
2,019		953,018,000
2,020		11,656,000
2,021		1,008,003,000
Thereafter		3,396,623,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		$ 5,905,991,000
Trust Preferred Securities
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 100,000,000
Trust Preferred Securities | LIBOR
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)		1.25%
Joint venture
Principal Repayments and Joint Venture Debt
2,018		$ 200,250,000
2,018		717,682,000
2,019		473,809,000
2,020		449,740,000
2,021		223,330,000
Thereafter		2,119,481,000
Long Term Debt, Maturities, Repayments of Principal		4,184,292,000
Joint venture | Trust Preferred Securities
Principal Repayments and Joint Venture Debt
2,018		0
2,018		0
2,019		0
2,020		0
2,021		0
Thereafter		100,000,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		100,000,000
Joint venture | Mortgages and other loans payable
Scheduled Amortization
2,018		37,971,000
2,018		42,289,000
2,019		23,487,000
2,020		11,656,000
2,021		9,448,000
Thereafter		16,675,000
Principal Repayments and Joint Venture Debt
2,018		206,431,000
2,018		0
2,019		679,531,000
2,020		0
2,021		198,555,000
Thereafter		1,639,948,000
Future Amortization of Debt		141,526,000
Long Term Debt, Maturities, Repayments of Principal		2,724,465,000
Joint venture | Revolving Credit Facility
Principal Repayments and Joint Venture Debt
2,018		0
2,018		0
2,019		0
2,020		0
2,021		0
Thereafter		40,000,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		40,000,000
Joint venture | Unsecured Term Loans
Principal Repayments and Joint Venture Debt
2,018		0
2,018		0
2,019		0
2,020		0
2,021		0
Thereafter		1,500,000,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		1,500,000,000
Joint venture | Senior Unsecured Notes
Principal Repayments and Joint Venture Debt
2,018		250,000,000
2,018		0
2,019		250,000,000
2,020		0
2,021		800,000,000
Thereafter		100,000,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		$ 1,400,000,000

Corporate Indebtedness - Schedu

Corporate Indebtedness - Schedule of Consolidated Interest Expense, Excluding Capitalized Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest expense
Interest expense before capitalized interest	$ 284,649	$ 348,062	$ 357,926
Interest capitalized	(26,020)	(24,067)	(31,108)
Interest income	(1,584)	(2,796)	(2,948)
Interest expense, net	$ 257,045	$ 321,199	$ 323,870

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Operating expenses, paid to related parties		$ 21,400	$ 21,890	$ 20,071
Amounts due from/to related parties
Due from joint ventures	$ 1,240	15,025	1,240
Other	14,616	8,014	14,616
Related party receivables	15,856	23,039	15,856
Alliance Building Services
Related Party Transaction [Line Items]
Profit participation from related party		3,900	3,500	3,800
Operating expenses, paid to related parties		22,600	23,400	21,300
Entity with Stephen L Green ownership interest
Related Party Transaction [Line Items]
Property management fees from related party		$ 500	700	$ 500
One Vanderbilt
Amounts due from/to related parties
Stabilization of property, within three years after stabilization, percent		50.00%
Stabilization of property, three years or more after stabilization, percent		100.00%
Stabilization of property, anniversary period		7 years
One Vanderbilt | Marc Holliday
Related Party Transaction [Line Items]
Due from (to) related party	1,400		1,400
One Vanderbilt | Andrew Mathias
Related Party Transaction [Line Items]
Due from (to) related party	$ 1,000		$ 1,000
One Vanderbilt | Minimum | Marc Holliday
Related Party Transaction [Line Items]
Percentage of profits due to investors	150.00%
One Vanderbilt | Minimum | Andrew Mathias
Related Party Transaction [Line Items]
Percentage of profits due to investors	100.00%
One Vanderbilt | Maximum | Marc Holliday
Related Party Transaction [Line Items]
Percentage of profits due to investors	180.00%
One Vanderbilt | Maximum | Andrew Mathias
Related Party Transaction [Line Items]
Percentage of profits due to investors	120.00%

Noncontrolling Interests on t91

Noncontrolling Interests on the Company's Consolidated Financial Statements - Additional Information (Details)	1 Months Ended	12 Months Ended
	Jan. 31, 2012$ / sharesshares	Dec. 31, 2017USD ($)shares$ / shares	Dec. 31, 2016USD ($)unit$ / sharesshares	Dec. 31, 2015USD ($)shares	Mar. 31, 2017shares	Jun. 30, 2016shares	Aug. 31, 2015shares	Jul. 31, 2015shares	Feb. 28, 2015shares	Aug. 31, 2014shares
Organization
Basic weighted average common shares outstanding (in shares)		98,571,000	100,185,000	99,345,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $		$ 473,882,000
Distributions | $		(52,446,000)	$ (15,419,000)	$ (119,784,000)
Redemption of common units | $				(20,650,000)
Net income | $		3,995,000	10,136,000	10,565,000
Accumulated other comprehensive income allocation | $		(94,000)	1,299,000	$ (67,000)
Balance at end of period | $		$ 461,954,000	$ 473,882,000
Number of company common stock issued on conversion of Series B preferred units		6.71348
Diluted weighted average common stock outstanding (shares)		103,403,000	104,881,000	103,734,000
SL Green Operating Partnership
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $		$ 473,882,000	$ 424,206,000
Distributions | $		(14,266,000)	(12,671,000)
Issuance of common units | $		25,723,000	78,495,000
Redemption of common units | $		(21,574,000)	(31,805,000)
Net income | $		3,995,000	10,136,000
Accumulated other comprehensive income allocation | $		(94,000)	1,299,000
Fair value adjustment | $		(5,712,000)	4,222,000
Balance at end of period | $		$ 461,954,000	$ 473,882,000	$ 424,206,000
SL Green Operating Partnership | Series G Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)	1,902,000
Dividend rate preferred units (as a percent)	4.50%
Liquidation preference of preferred units (in dollars per share) | $ / shares	$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		$ 1.125
Operating partnership common stock value use for conversion of preferred units (in dollars per share) | $ / shares		$ 88.50
Number of company common stock issue on redemption of operation partnership common units		1
SL Green Operating Partnership | Series F Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)		60
Mandatory liquidation preference (in dollars per share) | $		$ 1,000
SL Green Operating Partnership | Series K Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)										563,954
Dividend rate preferred units (as a percent)		3.50%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		0.875
Operating partnership common stock value use for conversion of preferred units (in dollars per share) | $ / shares		$ 134.67
Preferred Units, shares authorized		700,000
SL Green Operating Partnership | Series L Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)										378,634
Dividend rate preferred units (as a percent)		4.00%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		$ 1
Preferred Units, shares authorized		500,000
SL Green Operating Partnership | Series M Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)									1,600,000
Dividend rate preferred units (as a percent)		3.75%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		$ 0.9375
Preferred Units, shares authorized		1,600,000
SL Green Operating Partnership | Series N Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)						552,303
Dividend rate preferred units (as a percent)		3.00%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		$ 0.75
Preferred Units, shares authorized		552,303
SL Green Operating Partnership | Series O Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)		6.25%
Preferred Units, shares authorized		1
SL Green Operating Partnership | Series P Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)		200,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)								200,000
Dividend rate preferred units (as a percent)		4.00%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		$ 1
SL Green Operating Partnership | Series Q Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)		268,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)								268,000
Dividend rate preferred units (as a percent)		3.50%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		0.875
Operating partnership common stock value use for conversion of preferred units (in dollars per share) | $ / shares		$ 148.95
SL Green Operating Partnership | Series R Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)		400,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)							400,000
Dividend rate preferred units (as a percent)		3.50%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		0.875
Operating partnership common stock value use for conversion of preferred units (in dollars per share) | $ / shares		$ 154.89
SL Green Operating Partnership | Series S Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)		1,077,280
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)							1,077,280
Dividend rate preferred units (as a percent)		4.00%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		$ 1
SL Green Operating Partnership | Series T Preferred Stock
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)		230,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)					230,000
Dividend rate preferred units (as a percent)		2.75%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		0.6875
Operating partnership common stock value use for conversion of preferred units (in dollars per share) | $ / shares		$ 119.02
SL Green Operating Partnership | Series U Preferred Stock
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)		680,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)					680,000
Dividend rate preferred units (as a percent)		4.50%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25
Annual dividends on preferred units (in dollars per share) | $ / shares		$ 1.125
SL Green Operating Partnership | Series A Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)		109,161
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)							109,161
Dividend rate preferred units (as a percent)		3.50%
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 1,000
Annual dividends on preferred units (in dollars per share) | $ / shares		$ 35
SL Green Operating Partnership | Series B Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)		0
SL Green Operating Partnership
Organization
Basic weighted average common shares outstanding (in shares)		103,127,000	104,508,000	103,244,000
Noncontrolling interest in the operating partnership (as a percent)		4.58%	4.16%
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares)		4,452,979	4,363,716
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)		4,452,979
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Distributions | $		$ (52,446,000)	$ (15,419,000)	$ (119,784,000)
Redemption of common units | $				(20,650,000)
Accumulated other comprehensive income allocation | $		$ (94,000)	$ 1,299,000	$ (67,000)
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25	$ 25
Stock-based compensation plans (shares)		276,000	373,000	490,000
Diluted weighted average common stock outstanding (shares)		103,403,000	104,881,000	103,734,000
Minimum | SL Green Operating Partnership | Series U Preferred Stock
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Annual dividends on preferred units (in dollars per share) | $ / shares		$ 0.75

Noncontrolling Interests on t92

Noncontrolling Interests on the Company's Consolidated Financial Statements - Preferred Unit Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units			$ (20,650)
SL Green Operating Partnership
Rollforward Analysis of Preferred Unit Activity
Issuance of preferred units	$ 25,723	$ 78,495
Redemption of preferred units	(21,574)	(31,805)
SL Green Operating Partnership | Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period	302,010	282,516
Issuance of preferred units	0	22,793
Redemption of preferred units	(275)	(3,299)
Balance at end of period	$ 301,735	$ 302,010	$ 282,516

Stockholders' Equity of the C93

Stockholders' Equity of the Company - Additional Information (Details) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Authorized capital stock (shares)	260,000,000
Authorized shares, par value (in dollars per share)	$ 0.01
Common stock, shares authorized	160,000,000	160,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Excess stock, shares authorized (shares)	75,000,000
Excess stock, par value (in dollars per share)	$ 0.01
Preferred stock, shares authorized (shares)	25,000,000
Preferred stock, par	$ 0.01	$ 0.01
Excess shares issued (shares)	0

Stockholders' Equity of the C94

Stockholders' Equity of the Company - Stock Repurchase Program (Details) - USD ($)	1 Months Ended	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Aug. 31, 2016
Class of Stock [Line Items]
Number of shares purchased (in shares)		4,942,410	951,866	2,384,323	63,812
Maximum approximate dollar value of shares that may yet be purchased under the plan		$ 100.76	$ 101.67	$ 103.40	$ 103.84
2016 Repurchase Program
Class of Stock [Line Items]
Stock repurchase program, authorized amount	$ 500,000,000	$ 500,000,000				$ 1,000,000,000
Stock repurchase program, authorized amount, total	1,500,000,000	$ 1,500,000,000
Number of shares purchased (in shares)		8,342,411	3,400,001	2,448,135	63,812
Average price paid per share (in dollars per share)	$ 652,000,000	$ 652,000,000	$ 1,150,000,000	$ 1,246,800,000	$ 1,493,400,000
Repurchase of stock (in shares)	413,700

Stockholders' Equity of the C95

Stockholders' Equity of the Company - At-the-Market Equity Offering Program and Perpetual Preferred Stock (Details) - USD ($)	1 Months Ended	12 Months Ended
	Aug. 31, 2012	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Jun. 30, 2014	Jul. 31, 2011
Stockholders' Equity
Proceeds from sale of common stock		$ 0	$ 0	$ 124,761,000
Preferred stock, shares outstanding		9,200,000	9,200,000
Perpetual Preferred stock, liquidation preference (in dollars per share)		$ 25	$ 25
2011 ATM Equity Offering Program
Stockholders' Equity
Aggregate value of the shares of common stock to be sold							$ 250,000,000
Contributions - net proceeds from common stock offering (in shares)				25,659
Proceeds from sale of common stock				$ 2,800,000
2014 ATM Equity Offering Program
Stockholders' Equity
Aggregate value of the shares of common stock to be sold						$ 300,000,000
Contributions - net proceeds from common stock offering (in shares)				895,956
Proceeds from sale of common stock				$ 113,400,000
2015 ATM Equity Offering Program
Stockholders' Equity
Aggregate value of the shares of common stock to be sold					$ 300,000,000
Series I Preferred Stock
Stockholders' Equity
Preferred stock, shares outstanding	9,200,000	9,200,000
Dividend rate preferred units (as a percent)	6.50%	6.50%
Perpetual Preferred stock, liquidation preference (in dollars per share)		$ 25
Perpetual Preferred stock, annual dividends per share (in dollars per share)		$ 1.625
Contributions of net proceeds from sale of preferred stock	$ 221,900,000

Stockholders' Equity of the C96

Stockholders' Equity of the Company - Schedule of Common Stock Issued and Proceeds Received Dividend Reinvestments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 28, 2015
Stockholders' Equity
Common stock, shares authorized	160,000,000	160,000,000
Dividend reinvestments/stock purchases under the DRSPP	$ 0	$ 0	$ 124,761
Dividend Reinvestment and Stock Purchase Plan (DRIP)
Stockholders' Equity
Common stock, shares authorized				3,500,000
Issuance of common stock (in shares)	2,141	2,687	775,760
Dividend reinvestments/stock purchases under the DRSPP	$ 223	$ 277	$ 99,555

Stockholders' Equity of the C97

Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basic Earnings:
Income attributable to SL Green common stockholders	$ 27,982	$ 38,869	$ 8,222	$ 11,351	$ 44,016	$ 34,252	$ 133,457	$ 23,221	$ 86,424	$ 234,946	$ 269,132
Effect of Dilutive Securities:
Redemption of units to common shares									3,995	10,136	10,565
Diluted Earnings:
Income attributable to SL Green common stockholders									$ 90,419	$ 245,082	$ 279,697
Basic Shares:
Weighted average common shares outstanding (shares)									98,571,000	100,185,000	99,345,000
Effect of Dilutive Securities:
Redemption of units to common shares (shares)									4,556,000	4,323,000	3,899,000
Stock-based compensation plans (shares)									276,000	373,000	490,000
Diluted weighted average common stock outstanding (shares)									103,403,000	104,881,000	103,734,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,092,870	774,782	263,991

Partners' Capital of the Oper98

Partners' Capital of the Operating Partnership - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017shares	Dec. 31, 2016unitshares	Dec. 31, 2015shares	Dec. 31, 2014shares
Common Stock
Stockholders' Equity
Units outstanding (units)	92,803,000	100,562,000	99,976,000	97,325,000
SL Green Operating Partnership
Stockholders' Equity
Noncontrolling interest in the operating partnership (as a percent)	4.58%	4.16%
Number of units of operating partnership owned by the noncontrolling interest unit holders (units)	4,452,979	4,363,716
SL Green Operating Partnership | Series I Preferred Units
Stockholders' Equity
Units outstanding (units)	9,200,000
Common units redemption, period of restriction	1 year
Conversion of stock, shares issued (in shares)	1
SL Green Operating Partnership | Common Stock
Stockholders' Equity
Units outstanding (units)	92,803,299

Partners' Capital of the Oper99

Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Weighted average common shares outstanding (shares)									98,571,000	100,185,000	99,345,000
Diluted weighted average common stock outstanding (shares)									103,403,000	104,881,000	103,734,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,092,870	774,782	263,991
SL Green Operating Partnership
Net Income (Loss) Attributable to Parent [Abstract]
Net Income (Loss) Allocated to, Common Unitholders	$ 29,270	$ 40,681	$ 8,641	$ 11,827	$ 45,981	$ 35,915	$ 139,043	$ 24,143	$ 90,419	$ 245,082	$ 279,697
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Weighted average common shares outstanding (shares)									103,127,000	104,508,000	103,244,000
Stock-based compensation plans (shares)									276,000	373,000	490,000
Diluted weighted average common stock outstanding (shares)									103,403,000	104,881,000	103,734,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,092,870	774,782	263,991

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Details)	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2014shares	Aug. 31, 2011USD ($)	Dec. 31, 2017USD ($)unit / sharesfungible_unit$ / sharesshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares	Sep. 30, 2015shares	Jun. 30, 2015shares	Dec. 31, 2014shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options					$ 7,200,000	$ 6,000,000	$ 6,500,000
Stock options, stock appreciation rights and other awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of option (in years)					5 years
All other awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fungible units per share (in fungible units per share) | unit / shares					1
Expected life of option (in years)					10 years
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of option (in years)					4 years 4 months 24 days	3 years 8 months 12 days	3 years 7 months 6 days
Period of commencement of option vesting, from date of grant (in years)					1 year
Exercise price of options granted, low end of the range (in dollars per share) | $ / shares					$ 20.67
Exercise price of options granted, high end of the range (in dollars per share) | $ / shares					$ 137.18
Remaining weighted average contractual life of the options outstanding (in years)					3 years 7 months 12 days
Remaining weighted average contractual life of the options exercisable (in years)					3 years 1 month 24 days
Total unrecognized compensation cost related to unvested stock awards					$ 8,600,000
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)					1 year 6 months 6 days
Weighted average fair value of options granted during the period					$ 3,816,652	$ 8,363,036	$ 9,522,613
Stock options | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period (in years)					5 years
Options vesting period (in years)					1 year
Stock options | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period (in years)					10 years
Options vesting period (in years)					5 years
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual award vesting rate, low end of range (as a percent)					15.00%
Annual award vesting rate, high end of range (as a percent)					35.00%
Class O LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred unit distributions as a percentage of common unit distributions					10.00%
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense					$ 9,809,749	7,153,966	7,540,747
Total unrecognized compensation cost related to unvested stock awards					$ 21,100,000
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)					2 years 2 months 12 days
Fair value of restricted stock vested during the period					$ 9,400,000	7,600,000	7,400,000
Weighted average fair value of options granted during the period					$ 9,905,986	$ 10,650,077	$ 16,061,201
Awards granted (in shares) | shares					96,185	98,800	143,053
Awards outstanding (in shares) | shares					3,298,216	3,202,031	3,137,881			3,000,979
LTIP units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)					1 year 5 months 24 days
Weighted average fair value of options granted during the period					$ 20,500,000	$ 34,900,000
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost related to unvested stock awards					4,600,000
Share-based Compensation					$ 26,100,000	26,500,000	$ 30,200,000
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | shares					500,000
Shares of common stock available for issuance (shares)					85.00%
Duration of each offering period starting the first day of each calendar quarter (in months)					3 months
Shares of common stock issued (shares) | shares					104,597
Fourth Amended and Restated 2003 Stock Option and Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum fungible units that may be granted (in shares) | fungible_unit					27,030,000
Fungible units per share (in fungible units per share) | unit / shares					3.74
Shares that may be issued if equal to fungible units (shares) (less than) | shares					27,030,000
Fungible units | fungible_unit					8,300,000
Stock options, stock appreciation rights and other awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fungible units per share (in fungible units per share) | unit / shares					0.73
Third Amendment and Restated 2005 Stock Option and Incentive Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense					$ 7,800,000	8,900,000	8,000,000
2011 Outperformance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense					0	0	4,500,000
Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options						26,700,000
Approximate amount of LTIP units that may be earned by the recipients based on stock price appreciation				$ 85,000,000
LTIP units earned (in shares) | shares								280,454	560,908
Value of LTIP Units that could be earned expressed as percentage of outperformance amount in excess of the 30% benchmark (percent)				10.00%
Duration period return to stockholders exceeds 25% (in years)				3 years
Cumulative return to stockholders (percent)				25.00%
Return to stockholders				$ 85,000,000
Performance period (in years)				3 years
2011 Outperformance Plan | Vested on August 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of units vested				50.00%
2011 Outperformance Plan | Vesting on August 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of units vested				50.00%
2011 Outperformance Plan | Earned anytime after beginning of second year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of units vested				33.33%
2011 Outperformance Plan | Earned any time after beginning of third year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of units vested				66.67%
2014 Outperformance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense					13,600,000	$ 8,400,000	$ 5,900,000
Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options					27,900,000
Award period (in years)			3 years
Percentage of LTIP units that may be earned based on the Company's absolute total return to stockholders			66.67%
Percentage of LTIP units that may be earned based on relative total return to stockholders compared to constituents of the MSCI REIT index			33.33%
Awards granted (in shares) | shares			610,000
2014 Outperformance Plan | Vesting on August 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of units vested		50.00%
Deferred Stock Compensation Plan for Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense					$ 2,400,000
Maximum percentage of the annual retainer fee, chairman fees and meeting fees that may be deferred by non-employee directors (percent)					100.00%
Awards granted (in shares) | shares					12,727
Shares issued (in shares) | shares					9,509
Awards outstanding (in shares) | shares					99,853
Scenario, Forecast | 2014 Outperformance Plan | Vesting on August 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of units vested	50.00%

Share-based Compensation - Acti

Share-based Compensation - Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares held in employee trust (in shares)	104,597
Stock options
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Dividend yield (as a percent)	2.51%	2.37%	1.97%
Expected life of option (in years)	4 years 4 months 24 days	3 years 8 months 12 days	3 years 7 months 6 days
Risk-free interest rate (as a percent)	1.73%	1.57%	1.43%
Expected stock price volatility (as a percent)	28.10%	26.76%	32.34%
Options Outstanding
Balance at beginning of year (in shares)	1,737,213	1,595,007	1,462,726
Granted (in shares)	174,000	445,100	389,836
Exercised (in shares)	(292,193)	(192,875)	(217,438)
Lapsed or cancelled (in shares)	(70,301)	(110,019)	(40,117)
Balance at end of period (in shares)	1,548,719	1,737,213	1,595,007
Options exercisable at end of period (in shares)	800,902	748,617	589,055
Weighted average fair value of options granted during the period	$ 3,816,652	$ 8,363,036	$ 9,522,613
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 98.44	$ 95.52	$ 87.98
Granted (in dollars per share)	105.66	105.86	112.54
Exercised (in dollars per share)	81.07	76.90	74.69
Lapsed or cancelled (in dollars per share)	121.68	123.86	98.61
Balance at end of period (in dollars per share)	101.48	98.44	95.52
Options exercisable at end of period (in dollars per share)	$ 94.33	$ 87.72	$ 89.85
Restricted Stock Awards
Options Outstanding
Weighted average fair value of options granted during the period	$ 9,905,986	$ 10,650,077	$ 16,061,201
Summary of restricted stock
Balance at beginning of year (in shares)	3,202,031	3,137,881	3,000,979
Granted (in shares)	96,185	98,800	143,053
Cancelled (in shares)	0	(34,650)	(6,151)
Balance at end of period (in shares)	3,298,216	3,202,031	3,137,881
Vested during the period (in shares)	95,736	83,822	87,081
Compensation expense recorded	$ 9,809,749	$ 7,153,966	$ 7,540,747

Accumulated Other Comprehens102

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	$ 22,137	$ (8,749)	$ (6,980)
Other comprehensive income before reclassifications	(2,733)	18,211	(13,467)
Amounts reclassified from accumulated other comprehensive income	(800)	12,675	11,698
Ending Balance	18,604	22,137	(8,749)
Deferred net losses from terminated hedges	3,200	7,100
Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	12,596	(10,160)	(9,498)
Other comprehensive income before reclassifications	(1,618)	13,534	(11,143)
Amounts reclassified from accumulated other comprehensive income	1,564	9,222	10,481
Ending Balance	12,542	12,596	(10,160)
Net unrealized gain on marketable securities
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	5,520	2,003	2,613
Other comprehensive income before reclassifications	(1,348)	3,517	(610)
Amounts reclassified from accumulated other comprehensive income	(3,130)	0	0
Ending Balance	1,042	5,520	2,003
Joint venture | Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	4,021	(592)	(95)
Other comprehensive income before reclassifications	233	1,160	(1,714)
Amounts reclassified from accumulated other comprehensive income	766	3,453	1,217
Ending Balance	$ 5,020	$ 4,021	$ (592)

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value of Financial Instruments
Marketable securities	$ 28,579	$ 85,110
Interest rate cap and swap agreements (included in other assets)	16,692	21,090
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		1
Debt and preferred equity investments	2,114,041	1,640,412
Carrying Value
Fair Value of Financial Instruments
Fixed rate debt	4,305,165	5,452,084
Variable rate debt	1,605,431	1,105,585
Total	5,910,596	6,557,669
Fair Value
Fair Value of Financial Instruments
Marketable securities	28,579	85,110
Total	6,034,090	6,832,604
Level 1
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in other assets)	0	0
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		0
Level 2
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in other assets)	16,692	21,090
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		1
Level 3
Fair Value of Financial Instruments
Marketable securities	0	0
Interest rate cap and swap agreements (included in other assets)	0	0
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		0
Level 3 | Carrying Value
Fair Value of Financial Instruments
Debt and preferred equity investments		1,640,412
Level 3 | Fair Value
Fair Value of Financial Instruments
Fixed rate debt	4,421,866	5,722,494
Variable rate debt	1,612,224	1,110,110
Equity marketable securities
Fair Value of Financial Instruments
Marketable securities	0	48,315
Equity marketable securities | Level 1
Fair Value of Financial Instruments
Marketable securities	0	48,315
Mortgage-backed securities
Fair Value of Financial Instruments
Marketable securities	28,579	36,795
Mortgage-backed securities | Level 2
Fair Value of Financial Instruments
Marketable securities	28,579	36,795
Minimum | Fair Value
Fair Value of Financial Instruments
Estimated fair value of debt and preferred equity investments, low end of range	2,100,000	1,600,000
Maximum | Fair Value
Fair Value of Financial Instruments
Estimated fair value of debt and preferred equity investments, high end of range	2,300,000	$ 1,800,000
Total fixed rate | Mortgage and Jr Mortgage Loan with an Initial Maturity Date of April 2017
Fair Value of Financial Instruments
Notes receivable	250,000
Loans outstanding balance, amount in nonaccrual status	$ 259,300

Financial Instruments_ Deriv104

Financial Instruments: Derivatives and Hedging (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financial Instruments: Derivatives and Hedging
Fair Value	$ 16,692,000	$ 21,090,000
Gain (loss) from changes in fair value	(500,000)	500,000	$ 100,000
Fair value of derivatives in a net liability position	0
Aggregate termination value	0
Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion)	(2,482,000)	16,628,000	(13,386,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	2,856,000	11,502,000	12,157,000
Amount of (Loss) Gain Recognized into Income (Ineffective Portion)	60,000	757,000	(441,000)
Interest Rate Swap Expiring in July 2023
Financial Instruments: Derivatives and Hedging
Notional Value	$ 200,000,000
Strike Rate	1.131%
Fair Value	$ 10,747,000
Interest Rate Swap Expiring in July 2023, 2
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000,000
Strike Rate	1.161%
Fair Value	$ 5,217,000
Interest Rate Swap Expiring January 2019
Financial Instruments: Derivatives and Hedging
Notional Value	$ 21,394,000
Strike Rate	12.00%
Fair Value	$ 167,000
Interest Rate Cap Expiring September 2019
Financial Instruments: Derivatives and Hedging
Notional Value	$ 137,500,000
Strike Rate	4.00%
Fair Value	$ 2,000
Interest Rate Swap Expiring November 2020
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000,000
Strike Rate	1.928%
Fair Value	$ 288,000
Interest Rate Swap Expiring November 2020, 2
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000,000
Strike Rate	1.934%
Fair Value	$ 271,000
Interest Rate Swap
Financial Instruments: Derivatives and Hedging
Fair Value	16,692,000
Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion)	(2,282,000)	14,616,000	(11,607,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	1,821,000	9,521,000	10,892,000
Amount of (Loss) Gain Recognized into Income (Ineffective Portion)	5,000	(28,000)	(422,000)
Interest Expense
Financial Instruments: Derivatives and Hedging
Estimated current balance held in accumulated other comprehensive loss to be reclassified into earnings within the next 12 months	500,000
Income Loss From Equity Method Investments
Financial Instruments: Derivatives and Hedging
Estimated current balance held in accumulated other comprehensive loss to be reclassified into earnings within the next 12 months	(300,000)
Joint venture
Financial Instruments: Derivatives and Hedging
Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion)	(200,000)	2,012,000	(1,779,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	1,035,000	1,981,000	1,265,000
Amount of (Loss) Gain Recognized into Income (Ineffective Portion)	$ 55,000	$ 785,000	$ (19,000)

Rental Income (Details)

Rental Income (Details) $ in Thousands	Dec. 31, 2017USD ($)
Consolidated properties
Operating Leased Assets [Line Items]
2,018	$ 901,092
2,019	865,254
2,020	790,714
2,021	657,283
2,022	558,993
Thereafter	3,339,829
Total minimum lease payments	7,113,165
Unconsolidated properties
Operating Leased Assets [Line Items]
2,018	433,764
2,019	386,564
2,020	424,201
2,021	426,078
2,022	414,889
Thereafter	3,102,309
Total minimum lease payments	$ 5,187,805

Benefit Plans (Details)

Benefit Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Jun. 30, 2014
Multiemployer Plans [Line Items]
Plan contributions	$ 16,745,000		$ 17,092,000		$ 17,184,000
401 (K) Plan
Employee contribution limit per calendar year	15.00%
Employer matching contribution, percent of match	50.00%
Percentage of eligible compensation matched by employer	6.00%
Matching contribution	$ 728,782		566,000		550,000
Health Plan
Multiemployer Plans [Line Items]
Plan contributions	$ 11,426,000		11,530,000		8,736,000
Multiemployer plan, contributions by employer		$ 1,300,000,000		$ 1,200,000,000		$ 1,100,000,000
Percentage of contributions required for multiple collective-bargaining arrangements	5.00%
Other plans
Multiemployer Plans [Line Items]
Plan contributions	$ 1,463,000		1,583,000		5,716,000
Multiemployer Plans, Pension
Multiemployer Plans [Line Items]
Multiemployer plans, surcharge	No
Plan contributions	$ 3,856,000		$ 3,979,000	$ 257,800,000	$ 2,732,000	$ 249,500,000	$ 221,900,000
Multiemployer plans, contributions by employer, percent	5.00%

Commitments and Contingencie107

Commitments and Contingencies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)options	Dec. 31, 2016USD ($)
Other Commitments [Line Items]
Employment agreements with certain executives, minimum cash-based compensation for next fiscal year	$ 5,400
Employment agreements with certain executives, grant date value of deferred compensation awards	1,600
Capital lease obligations	$ 42,843	$ 42,132
Initial term of non cancellable operating leases, minimum (in years)	1 year
Capital lease
2,018	$ 2,387
2,017	2,411
2,018	2,620
2,019	2,794
2,020	2,794
Thereafter	819,894
Total minimum lease payments	832,900
Amount representing interest	(790,057)
Capital lease obligations	42,843
Non-cancellable operating leases
2,018	31,049
2,017	31,066
2,018	31,436
2,019	31,628
2,020	29,472
Thereafter	703,254
Total minimum lease payments	$ 857,905
30 East 40th Street
Other Commitments [Line Items]
Land as percentage of fair market value of property under lease	63.60%
Capital lease obligations	$ 20,000
Non-cancellable operating leases
Total minimum lease payments	$ 76,000
420 Lexington Avenue
Other Commitments [Line Items]
Land as percentage of fair market value of property under lease	6.00%
Annual ground lease payments through December 2019	$ 10,900
Annual ground lease payments through December 2029	11,200
Annual ground lease payments due thereafter	$ 12,300
Number of renewal options available (extension option) | options	2
Term of first renewal option (in years)	35 years
Term of second renewal option (in years)	35 years
1080 Amsterdam Avenue
Other Commitments [Line Items]
Land as percentage of fair market value of property under lease	40.00%
Non-cancellable operating leases
Total minimum lease payments	$ 41,600
711 Third Avenue
Other Commitments [Line Items]
Number of renewal options available (extension option) | options	5
Term of first renewal option (in years)	10 years
Percentage of the fee not owned by the entity (percent)	50.00%
Term of second renewal option (in years)	10 years
Term of third renewal option	10 years
711 Third Avenue | Through July 2016
Other Commitments [Line Items]
Required annual ground lease payments	$ 5,250
711 Third Avenue | After July 2016
Other Commitments [Line Items]
Required annual ground lease payments	$ 5,500
461 Fifth Avenue
Other Commitments [Line Items]
Number of renewal options available (extension option) | options	2
Term of first renewal option (in years)	21 years
Required annual ground lease payments	$ 2,100
Term of second renewal option (in years)	21 years
Term of third renewal option	15 years
625 Madison Avenue
Other Commitments [Line Items]
Number of renewal options available (extension option) | options	2
Term of first renewal option (in years)	23 years
Required annual ground lease payments	$ 4,600
Term of second renewal option (in years)	23 years
1185 Avenue of the Americas
Other Commitments [Line Items]
Term of first renewal option (in years)	23 years
Required annual ground lease payments	$ 6,900
1055 Washington Boulevard
Other Commitments [Line Items]
Required annual ground lease payments	600
Belmont
Other Commitments [Line Items]
Loss reserves	$ 5,500	$ 6,300

Segment Information - Additiona

Segment Information - Additional Information (Details) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Segment information
Number of reportable segments (segment) | segment										2
Total revenues		$ 361,342	$ 374,600	$ 398,150	$ 377,381	$ 374,242	$ 416,681	$ 617,614	$ 455,444	$ 1,511,473	$ 1,863,981	$ 1,662,829
Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and gain (loss) on sale of marketable securities										186,920	7,256	90,289
Total assets	[1]	13,982,904				15,857,787				13,982,904	15,857,787
Marketing, general and administrative										100,498	99,759	94,873
Operating Segments | Real Estate Segment
Segment information
Total revenues										1,317,602	1,650,973	1,481,701
Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and gain (loss) on sale of marketable securities										16,557	(197,000)	(71,634)
Total assets		11,696,560				13,868,672				11,696,560	13,868,672
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues										193,871	213,008	181,128
Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and gain (loss) on sale of marketable securities										170,363	204,256	$ 161,923
Total assets		$ 2,286,344				$ 1,989,115				$ 2,286,344	$ 1,989,115
[1]	The Company's consolidated balance sheets include assets and liabilities of consolidated variable interest entities ("VIEs"). See Note 2. The consolidated balance sheets include the following amounts related to our consolidated VIEs, excluding the Operating Partnership: $398.0 million and $412.3 million of land, $1.4 billion and $1.5 billion of building and improvements, $2.0 million and $2.0 million of building and leasehold improvements, $47.4 million and $47.4 million of properties under capital lease, $330.9 million and $327.2 million of accumulated depreciation, $221.0 million and $226.8 million of other assets included in other line items, $628.9 million and $621.8 million of real estate debt, net, $2.5 million and $2.2 million of accrued interest payable, $42.8 million and $42.1 million of capital lease obligations, and $56.8 million and $72.2 million of other liabilities included in other line items as of December 31, 2017 and December 31, 2016, respectively.

Segment Information - Schedule

Segment Information - Schedule of Reconciliation of Income from Continuing Operations to Net Income Attributable to SL Green Common Stockholders (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of income from continuing operations to net income attributable to SL Green common stockholders
Income from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves, loss on early extinguishment of debt, and gain (loss) on sale of marketable securities									$ 186,920	$ 7,256	$ 90,289
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	$ 0	$ 1,030	$ 13,089	$ 2,047	$ 421	$ 225	$ 33,448	$ 9,915	16,166	44,009	15,844
Purchase price fair value adjustment									0	0	40,078
Gain on sale of real estate, net	76,497	0	(3,823)	567	27,366	397	196,580	13,773	73,241	238,116	175,974
Depreciable real estate reserves	$ (93,184)	$ 0	$ (29,064)	$ (56,272)	$ 0	$ 0	$ (10,387)	$ 0	(178,520)	(10,387)	(19,226)
Loss on early extinguishment of debt									0	0	(49)
(Loss) gain on sale of investment in marketable securities									3,262	(83)	0
Income from continuing operations									101,069	278,911	302,910
Net income from discontinued operations									0	0	427
Gain on sale of discontinued operations									0	0	14,122
Net income									$ 101,069	$ 278,911	$ 317,459

Quarterly Financial Data of 110

Quarterly Financial Data of the Company (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Income Statements, Captions [Line Items]
Total revenues	$ 361,342	$ 374,600	$ 398,150	$ 377,381	$ 374,242	$ 416,681	$ 617,614	$ 455,444	$ 1,511,473	$ 1,863,981	$ 1,662,829
Income (loss) from continuing operations before equity in net income from unconsolidated joint ventures, equity in net (loss) gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves and gain (loss) on early extinguishment of debt	47,234	40,687	32,401	44,706	26,278	46,689	(76,304)	(1,281)	165,028	(4,618)	77,261
Equity in net income from unconsolidated joint ventures	7,788	4,078	3,412	6,614	(95)	(3,968)	5,841	10,096	21,892	11,874	13,028
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	0	1,030	13,089	2,047	421	225	33,448	9,915	16,166	44,009	15,844
Gain on sale of real estate, net	76,497	0	(3,823)	567	27,366	397	196,580	13,773	73,241	238,116	175,974
Depreciable real estate reserves	(93,184)	0	(29,064)	(56,272)	0	0	(10,387)	0	(178,520)	(10,387)	(19,226)
Change in unrealized gain (loss) on marketable securities	0	0	0	3,262	0	0	(83)	0
Distributions Preferred Units	(6,616)	(3,188)	(4,056)	14,165	(6,217)	(5,353)	(11,901)	(5,544)
Net income from discontinued operations									0	0	427
Gain on sale of discontinued operations									0	0	14,122
Net income (loss) attributable to SL Green/SLGOP	31,719	42,607	11,959	15,089	47,753	37,990	137,194	26,959	101,374	249,896	284,084
Perpetual preferred stock dividends	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(14,950)	(14,950)	(14,952)
Net income attributable to SL Green common stockholders	$ 27,982	$ 38,869	$ 8,222	$ 11,351	$ 44,016	$ 34,252	$ 133,457	$ 23,221	$ 86,424	$ 234,946	$ 269,132
Net income (loss) attributable to common stockholders per common share - basic (usd per share)	$ 0.29	$ 0.40	$ 0.08	$ 0.11	$ 0.44	$ 0.34	$ 1.33	$ 0.23	$ 0.88	$ 2.35	$ 2.71
Net income (loss) attributable to common stockholders per common share - diluted (usd per share)	$ 0.29	$ 0.40	$ 0.08	$ 0.11	$ 0.44	$ 0.34	$ 1.33	$ 0.23	$ 0.87	$ 2.34	$ 2.70

Quarterly Financial Data of 111

Quarterly Financial Data of the Operating Partnership (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Income Statements, Captions [Line Items]
Total revenues	$ 361,342	$ 374,600	$ 398,150	$ 377,381	$ 374,242	$ 416,681	$ 617,614	$ 455,444	$ 1,511,473	$ 1,863,981	$ 1,662,829
Income (loss) from continuing operations before equity in net income from unconsolidated joint ventures, equity in net (loss) gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves and gain (loss) on early extinguishment of debt	47,234	40,687	32,401	44,706	26,278	46,689	(76,304)	(1,281)	165,028	(4,618)	77,261
Equity in net income from unconsolidated joint ventures	7,788	4,078	3,412	6,614	(95)	(3,968)	5,841	10,096	21,892	11,874	13,028
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	0	1,030	13,089	2,047	421	225	33,448	9,915	16,166	44,009	15,844
Purchase price fair value adjustment									0	0	38,563
Gain (loss) on sale of real estate, net	76,497	0	(3,823)	567	27,366	397	196,580	13,773	73,241	238,116	175,974
Depreciable real estate reserves	(93,184)	0	(29,064)	(56,272)	0	0	(10,387)	0	(178,520)	(10,387)	(19,226)
Loss on early extinguishment of debt									0	0	(49)
Distributions Preferred Units	(6,616)	(3,188)	(4,056)	14,165	(6,217)	(5,353)	(11,901)	(5,544)
Net income (loss) attributable to SL Green/SLGOP	31,719	42,607	11,959	15,089	47,753	37,990	137,194	26,959	101,374	249,896	284,084
Preferred stock/unit redemption costs									0	0	0
SL Green Operating Partnership
Condensed Income Statements, Captions [Line Items]
Total revenues	361,342	374,600	398,150	377,381	374,242	416,681	617,614	455,444	1,511,473	1,863,981	1,662,829
Income (loss) from continuing operations before equity in net income from unconsolidated joint ventures, equity in net (loss) gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves and gain (loss) on early extinguishment of debt	47,234	40,687	32,401	44,706	26,278	46,689	(76,304)	(1,281)	165,028	(4,618)	77,261
Equity in net income from unconsolidated joint ventures	7,788	4,078	3,412	6,614	(95)	(3,968)	5,841	10,096	21,892	11,874	13,028
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	0	1,030	13,089	2,047	421	225	33,448	9,915	16,166	44,009	15,844
Purchase price fair value adjustment									0	0	40,078
Gain (loss) on sale of real estate, net	76,497	0	(3,823)	567	27,366	397	196,580	13,773	73,241	238,116	175,974
Depreciable real estate reserves	(93,184)	0	(29,064)	(56,272)	0	0	(10,387)	0	(178,520)	(10,387)	(19,226)
Loss on early extinguishment of debt	0	0	0	3,262	0	0	(83)	0	0	0	(49)
Distributions Preferred Units	(5,328)	(1,376)	(3,637)	14,641	(4,252)	(3,690)	(6,315)	(4,622)	(14,950)	(14,950)	(14,952)
Net income (loss) attributable to SL Green/SLGOP	33,007	44,419	12,378	15,565	49,718	39,653	142,780	27,881	105,369	260,032	294,649
Preferred stock/unit redemption costs									0	0	0
Perpetual preferred units distributions	3,737	3,738	3,737	3,738	3,737	3,738	3,737	3,738	(14,950)	(14,950)	(14,952)
Net income attributable to SLGOP common unitholders	$ 29,270	$ 40,681	$ 8,641	$ 11,827	$ 45,981	$ 35,915	$ 139,043	$ 24,143	$ 90,419	$ 245,082	$ 279,697
Net income attributable to common unitholders per common unit - basic (usd per share)	$ 0.29	$ 0.40	$ 0.08	$ 0.11	$ 0.44	$ 0.34	$ 1.33	$ 0.23	$ 0.88	$ 2.35	$ 2.71
Net Income (Loss), Net of Tax, Per Outstanding Limited Partnership Unit, Diluted	$ 0.29	$ 0.40	$ 0.08	$ 0.11	$ 0.44	$ 0.34	$ 1.33	$ 0.23	$ 0.87	$ 2.34	$ 2.70

Schedule II - Valuation and 112

Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tenant and other receivables—allowance
Changes in valuation allowance
Balance at Beginning of Year	$ 16,592	$ 17,618	$ 18,068
Additions Charged Against Operations	6,106	10,630	8,139
Uncollectible Accounts Written-off/Recovery (1)	(4,061)	(11,656)	(8,589)
Balance at End of Year	18,637	16,592	17,618
Deferred rent receivable—allowance
Changes in valuation allowance
Balance at Beginning of Year	25,203	21,730	27,411
Additions Charged Against Operations	2,321	13,620	2,789
Uncollectible Accounts Written-off/Recovery (1)	(10,317)	(10,147)	(8,470)
Balance at End of Year	$ 17,207	$ 25,203	$ 21,730

Schedule III - Real Estate a113

Schedule III - Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 2,755,182
Initial Cost
Land	2,374,414
Building & Improvements	6,492,236
Cost Capitalized Subsequent To Acquisition
Land	(17,363)
Building & Improvements	1,356,835
Gross Amount at Which Carried at Close of Period
Land	2,357,051
Building & Improvements	7,849,071
Total	10,206,122	$ 12,743,332	$ 16,681,602	$ 14,069,141
Accumulated Depreciation	2,300,116	$ 2,264,694	$ 2,060,706	$ 1,905,165
420 Lexington Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	300,000
Initial Cost
Land	0
Building & Improvements	107,832
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	253,314
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	361,146
Total	361,146
Accumulated Depreciation	157,502
711 Third Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	19,844
Building & Improvements	42,499
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	66,553
Gross Amount at Which Carried at Close of Period
Land	19,844
Building & Improvements	109,052
Total	128,896
Accumulated Depreciation	$ 39,396
Interest in property (as a percent)	50.00%
Third Avenue, 919 [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 500,000
Initial Cost
Land	223,529
Building & Improvements	1,033,198
Cost Capitalized Subsequent To Acquisition
Land	35,410
Building & Improvements	68,413
Gross Amount at Which Carried at Close of Period
Land	258,939
Building & Improvements	1,101,611
Total	1,360,550
Accumulated Depreciation	$ 303,424
Interest in property (as a percent)	51.00%
555 W. 57th Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost
Land	18,846
Building & Improvements	78,704
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	61,424
Gross Amount at Which Carried at Close of Period
Land	18,846
Building & Improvements	140,128
Total	158,974
Accumulated Depreciation	64,281
220 East 42nd Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	275,000
Initial Cost
Land	50,373
Building & Improvements	203,727
Cost Capitalized Subsequent To Acquisition
Land	635
Building & Improvements	143,059
Gross Amount at Which Carried at Close of Period
Land	51,008
Building & Improvements	346,786
Total	397,794
Accumulated Depreciation	97,895
461 Fifth Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	0
Building & Improvements	62,695
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	16,185
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	78,880
Total	78,880
Accumulated Depreciation	28,378
750 Third Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	51,093
Building & Improvements	205,972
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	42,543
Gross Amount at Which Carried at Close of Period
Land	51,093
Building & Improvements	248,515
Total	299,608
Accumulated Depreciation	93,469
625 Madison Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	0
Building & Improvements	246,673
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	43,175
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	289,848
Total	289,848
Accumulated Depreciation	107,791
485 Lexington Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	450,000
Initial Cost
Land	77,517
Building & Improvements	326,825
Cost Capitalized Subsequent To Acquisition
Land	765
Building & Improvements	110,648
Gross Amount at Which Carried at Close of Period
Land	78,282
Building & Improvements	437,473
Total	515,755
Accumulated Depreciation	168,921
609 Fifth Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	36,677
Building & Improvements	145,954
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	10,435
Gross Amount at Which Carried at Close of Period
Land	36,677
Building & Improvements	156,389
Total	193,066
Accumulated Depreciation	46,059
810 Seventh Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	114,077
Building & Improvements	476,386
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	71,735
Gross Amount at Which Carried at Close of Period
Land	114,077
Building & Improvements	548,121
Total	662,198
Accumulated Depreciation	162,606
1185 Avenue of the Americas
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	0
Building & Improvements	728,213
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	47,793
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	776,006
Total	776,006
Accumulated Depreciation	242,681
1350 Avenue of the Americas
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	91,038
Building & Improvements	380,744
Cost Capitalized Subsequent To Acquisition
Land	(97)
Building & Improvements	41,911
Gross Amount at Which Carried at Close of Period
Land	90,941
Building & Improvements	422,655
Total	513,596
Accumulated Depreciation	124,638
100 Summit Lake Drive
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	10,526
Building & Improvements	43,109
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	11,215
Gross Amount at Which Carried at Close of Period
Land	10,526
Building & Improvements	54,324
Total	64,850
Accumulated Depreciation	16,963
200 Summit Lake Drive
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	11,183
Building & Improvements	47,906
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	11,177
Gross Amount at Which Carried at Close of Period
Land	11,183
Building & Improvements	59,083
Total	70,266
Accumulated Depreciation	18,818
500 Summit Lake Drive
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	9,777
Building & Improvements	39,048
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	6,358
Gross Amount at Which Carried at Close of Period
Land	9,777
Building & Improvements	45,406
Total	55,183
Accumulated Depreciation	13,074
360 Hamilton Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	29,497
Building & Improvements	118,250
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	15,392
Gross Amount at Which Carried at Close of Period
Land	29,497
Building & Improvements	133,642
Total	163,139
Accumulated Depreciation	39,811
1-6 Landmark Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	100,000
Initial Cost
Land	50,947
Building & Improvements	195,167
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	51,515
Gross Amount at Which Carried at Close of Period
Land	50,947
Building & Improvements	246,682
Total	297,629
Accumulated Depreciation	70,120
7 Landmark Square
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	2,088
Building & Improvements	7,748
Cost Capitalized Subsequent To Acquisition
Land	(367)
Building & Improvements	670
Gross Amount at Which Carried at Close of Period
Land	1,721
Building & Improvements	8,418
Total	10,139
Accumulated Depreciation	$ 1,286
680 Washington Boulevard
Gross Amount at Which Carried at Close of Period
Interest in property (as a percent)	51.00%
750 Washington Boulevard
Gross Amount at Which Carried at Close of Period
Interest in property (as a percent)	51.00%
1010 Washington Boulevard
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost
Land	7,747
Building & Improvements	30,423
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	7,378
Gross Amount at Which Carried at Close of Period
Land	7,747
Building & Improvements	37,801
Total	45,548
Accumulated Depreciation	11,044
400 Summit Lake Drive
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	38,889
Building & Improvements	1
Cost Capitalized Subsequent To Acquisition
Land	285
Building & Improvements	2
Gross Amount at Which Carried at Close of Period
Land	39,174
Building & Improvements	3
Total	39,177
Accumulated Depreciation	0
1055 Washington Boulevard
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	13,516
Building & Improvements	53,228
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	8,390
Gross Amount at Which Carried at Close of Period
Land	13,516
Building & Improvements	61,618
Total	75,134
Accumulated Depreciation	18,075
1 Madison Ave
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	486,153
Initial Cost
Land	172,641
Building & Improvements	654,394
Cost Capitalized Subsequent To Acquisition
Land	905
Building & Improvements	15,801
Gross Amount at Which Carried at Close of Period
Land	173,546
Building & Improvements	670,195
Total	843,741
Accumulated Depreciation	175,971
100 Church Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	217,273
Initial Cost
Land	32,494
Building & Improvements	79,996
Cost Capitalized Subsequent To Acquisition
Land	2,500
Building & Improvements	96,027
Gross Amount at Which Carried at Close of Period
Land	34,994
Building & Improvements	176,023
Total	211,017
Accumulated Depreciation	46,825
125 Park Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	120,900
Building & Improvements	189,714
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	74,660
Gross Amount at Which Carried at Close of Period
Land	120,900
Building & Improvements	264,374
Total	385,274
Accumulated Depreciation	65,529
Williamsburg
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	3,677
Building & Improvements	14,708
Cost Capitalized Subsequent To Acquisition
Land	2,523
Building & Improvements	(4,550)
Gross Amount at Which Carried at Close of Period
Land	6,200
Building & Improvements	10,158
Total	16,358
Accumulated Depreciation	1,865
110 East 42nd Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	34,000
Building & Improvements	46,411
Cost Capitalized Subsequent To Acquisition
Land	2,196
Building & Improvements	27,253
Gross Amount at Which Carried at Close of Period
Land	36,196
Building & Improvements	73,664
Total	109,860
Accumulated Depreciation	17,603
East 400 Street 58 [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	40,000
Initial Cost
Land	17,549
Building & Improvements	30,916
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	7,590
Gross Amount at Which Carried at Close of Period
Land	17,549
Building & Improvements	38,506
Total	56,055
Accumulated Depreciation	$ 5,154
Interest in property (as a percent)	90.00%
752 Madison Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost
Land	282,415
Building & Improvements	7,131
Cost Capitalized Subsequent To Acquisition
Land	1,871
Building & Improvements	58
Gross Amount at Which Carried at Close of Period
Land	284,286
Building & Improvements	7,189
Total	291,475
Accumulated Depreciation	1,180
762 Madison Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	771
Initial Cost
Land	6,153
Building & Improvements	10,461
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	131
Gross Amount at Which Carried at Close of Period
Land	6,153
Building & Improvements	10,592
Total	16,745
Accumulated Depreciation	$ 1,627
Interest in property (as a percent)	90.00%
19-21 East 65th Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost
Land	0
Building & Improvements	7,389
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	364
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	7,753
Total	7,753
Accumulated Depreciation	$ 1,141
Interest in property (as a percent)	90.00%
304 Park Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost
Land	54,189
Building & Improvements	75,619
Cost Capitalized Subsequent To Acquisition
Land	300
Building & Improvements	14,550
Gross Amount at Which Carried at Close of Period
Land	54,489
Building & Improvements	90,169
Total	144,658
Accumulated Depreciation	16,445
635 Sixth Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	24,180
Building & Improvements	37,158
Cost Capitalized Subsequent To Acquisition
Land	163
Building & Improvements	51,805
Gross Amount at Which Carried at Close of Period
Land	24,343
Building & Improvements	88,963
Total	113,306
Accumulated Depreciation	7,854
641 Sixth Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	45,668
Building & Improvements	67,316
Cost Capitalized Subsequent To Acquisition
Land	308
Building & Improvements	6,029
Gross Amount at Which Carried at Close of Period
Land	45,976
Building & Improvements	73,345
Total	119,321
Accumulated Depreciation	12,097
1080 Amsterdam
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	36,363
Initial Cost
Land	0
Building & Improvements	27,445
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	20,489
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	47,934
Total	47,934
Accumulated Depreciation	$ 4,216
Interest in property (as a percent)	92.50%
315 West 33rd Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 250,000
Initial Cost
Land	195,834
Building & Improvements	164,429
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	11,583
Gross Amount at Which Carried at Close of Period
Land	195,834
Building & Improvements	176,012
Total	371,846
Accumulated Depreciation	19,966
562 Fifth Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	57,052
Building & Improvements	10,487
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	1,213
Gross Amount at Which Carried at Close of Period
Land	57,052
Building & Improvements	11,700
Total	68,752
Accumulated Depreciation	3,596
719 Seventh Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	41,622
Initial Cost
Land	41,850
Building & Improvements	0
Cost Capitalized Subsequent To Acquisition
Land	2,336
Building & Improvements	34,055
Gross Amount at Which Carried at Close of Period
Land	44,186
Building & Improvements	34,055
Total	78,241
Accumulated Depreciation	$ 215
Interest in property (as a percent)	75.00%
115 Spring Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost
Land	11,078
Building & Improvements	44,799
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	1,759
Gross Amount at Which Carried at Close of Period
Land	11,078
Building & Improvements	46,558
Total	57,636
Accumulated Depreciation	4,083
635 Madison Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	205,632
Building & Improvements	15,805
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	0
Gross Amount at Which Carried at Close of Period
Land	205,632
Building & Improvements	15,805
Total	221,437
Accumulated Depreciation	1,306
1640 Flatbush Avenue
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	6,226
Building & Improvements	501
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	231
Gross Amount at Which Carried at Close of Period
Land	6,226
Building & Improvements	732
Total	6,958
Accumulated Depreciation	35
One Vanderbilt
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	80,069
Building & Improvements	116,557
Cost Capitalized Subsequent To Acquisition
Land	(80,069)
Building & Improvements	(116,558)
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	(1)
Total	(1)
Accumulated Depreciation	0
Upper East Side Residential
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	48,152
Building & Improvements	0
Cost Capitalized Subsequent To Acquisition
Land	13,323
Building & Improvements	0
Gross Amount at Which Carried at Close of Period
Land	61,475
Building & Improvements	0
Total	61,475
Accumulated Depreciation	$ 0
Interest in property (as a percent)	95.10%
110 Greene Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost
Land	45,120
Building & Improvements	215,470
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	9,611
Gross Amount at Which Carried at Close of Period
Land	45,120
Building & Improvements	225,081
Total	270,201
Accumulated Depreciation	$ 15,693
Interest in property (as a percent)	90.00%
187 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost
Land	7,600
Building & Improvements	9,412
Cost Capitalized Subsequent To Acquisition
Land	(7,600)
Building & Improvements	(154)
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	9,258
Total	9,258
Accumulated Depreciation	9,258
5- 7 Dey Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	58,000
Initial Cost
Land	13,400
Building & Improvements	34,175
Cost Capitalized Subsequent To Acquisition
Land	13,050
Building & Improvements	10,481
Gross Amount at Which Carried at Close of Period
Land	26,450
Building & Improvements	44,656
Total	71,106
Accumulated Depreciation	34,136
30 East 40th Street
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	4,650
Building & Improvements	20,000
Cost Capitalized Subsequent To Acquisition
Land	2
Building & Improvements	4,197
Gross Amount at Which Carried at Close of Period
Land	4,652
Building & Improvements	24,197
Total	28,849
Accumulated Depreciation	534
183 Broadway
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	5,799
Building & Improvements	23,431
Cost Capitalized Subsequent To Acquisition
Land	(5,799)
Building & Improvements	923
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	24,354
Total	24,354
Accumulated Depreciation	24,354
Other
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	922
Building & Improvements	14,210
Cost Capitalized Subsequent To Acquisition
Land	(3)
Building & Improvements	2
Gross Amount at Which Carried at Close of Period
Land	919
Building & Improvements	14,212
Total	15,131
Accumulated Depreciation	$ 3,201

Schedule III - Real Estate a114

Schedule III - Real Estate and Accumulated Depreciation (Activity in Real Estate and Accumulated Depreciation)(Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in real estate
Balance at beginning of year	$ 12,743,332	$ 16,681,602
Property acquisitions	13,323	29,230	$ 3,064,137
Improvements	342,014	426,060	396,555
Retirements/disposals/deconsolidation	(2,892,547)	(4,393,560)	(848,231)
Balance at end of year	10,206,122	12,743,332	16,681,602
Aggregate cost of land, buildings and improvements before depreciation	9,200,000
Changes in accumulated depreciation
Balance at beginning of year	2,264,694	2,060,706
Depreciation for year	347,015	353,502	480,523
Retirements/disposals/deconsolidation	(311,593)	(149,514)	(324,982)
Balance at end of year	$ 2,300,116	$ 2,264,694	$ 2,060,706