SL Green Realty (SLG) 10-K 27 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 25, 2019	Jun. 30, 2018
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, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	FY
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		84,325,436
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 8,000,000,000
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, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	FY
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,022,921
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 ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Commercial real estate properties, at cost:
Land and land interests		$ 1,774,899	$ 2,357,051
Building and improvements		5,268,484	6,351,012
Building leasehold and improvements		1,423,107	1,450,614
Properties under capital lease		47,445	47,445
Total commercial real estate properties, at cost		8,513,935	10,206,122
Less: accumulated depreciation		(2,099,137)	(2,300,116)
Total commercial real estate properties, net		6,414,798	7,906,006
Assets held for sale		0	338,354
Cash and cash equivalents		129,475	127,888
Restricted cash		149,638	122,138
Investments in marketable securities		28,638	28,579
Tenant and other receivables, net of allowance of $15,702 and $18,637 in 2018 and 2017, respectively		41,589	57,644
Related party receivables		28,033	23,039
Deferred rents receivable, net of allowance of $15,457 and $17,207 in 2018 and 2017, respectively		335,985	365,337
Debt and preferred equity investments, net of discounts and deferred origination fees of $22,379 and $25,507 in 2018 and 2017, respectively, and allowance of $5,750 in 2018		2,099,393	2,114,041
Investments in unconsolidated joint ventures		3,019,020	2,362,989
Deferred costs, net		209,110	226,201
Other assets		295,679	310,688
Total assets	[1]	12,751,358	13,982,904
Liabilities
Mortgages and other loans payable, net		1,961,240	2,837,282
Revolving credit facility, net		492,196	30,336
Unsecured term loans, net		1,493,051	1,491,575
Unsecured notes, net		1,495,214	1,395,939
Accrued interest payable		23,154	38,142
Other liabilities		116,566	188,005
Accounts payable and accrued expenses		147,060	137,142
Deferred revenue		94,453	208,119
Capital lease obligations		43,616	42,843
Deferred land leases payable		3,603	3,239
Dividend and distributions payable		80,430	85,138
Security deposits		64,688	67,927
Liabilities related to assets held for sale		0	4,074
Junior subordinated deferrable interest debentures held by trusts that issued trust preferred securities		100,000	100,000
Total liabilities	[1]	6,115,271	6,629,761
Commitments and contingencies
Noncontrolling interests in Operating Partnership		387,805	461,954
Preferred units		300,427	301,735
Equity
Series I Preferred Stock, $0.01 par value, $25.00 liquidation preference, 9,200 issued and outstanding at both December 31, 2018 and 2017		221,932	221,932
Common stock, $0.01 par value, 160,000 shares authorized and 84,739 and 93,858 issued and outstanding at December 31, 2018 and 2017, respectively (including 1,055 and 1,055 shares held in treasury at December 31, 2018 and 2017, respectively)		847	939
Additional paid-in-capital		4,508,685	4,968,338
Treasury stock at cost		(124,049)	(124,049)
Accumulated other comprehensive income		15,108	18,604
Retained earnings		1,278,998	1,139,329
Total SL Green stockholders' equity		5,901,521	6,225,093
Noncontrolling interests in other partnerships		46,334	364,361
Total equity		5,947,855	6,589,454
SL Green stockholders equity:
Total liabilities and equity/capital		12,751,358	13,982,904
SL Green Operating Partnership
Commercial real estate properties, at cost:
Land and land interests		1,774,899	2,357,051
Building and improvements		5,268,484	6,351,012
Building leasehold and improvements		1,423,107	1,450,614
Properties under capital lease		47,445	47,445
Total commercial real estate properties, at cost		8,513,935	10,206,122
Less: accumulated depreciation		(2,099,137)	(2,300,116)
Total commercial real estate properties, net		6,414,798	7,906,006
Assets held for sale		0	338,354
Cash and cash equivalents		129,475	127,888
Restricted cash		149,638	122,138
Investments in marketable securities		28,638	28,579
Tenant and other receivables, net of allowance of $15,702 and $18,637 in 2018 and 2017, respectively		41,589	57,644
Related party receivables		28,033	23,039
Deferred rents receivable, net of allowance of $15,457 and $17,207 in 2018 and 2017, respectively		335,985	365,337
Debt and preferred equity investments, net of discounts and deferred origination fees of $22,379 and $25,507 in 2018 and 2017, respectively, and allowance of $5,750 in 2018		2,099,393	2,114,041
Investments in unconsolidated joint ventures		3,019,020	2,362,989
Deferred costs, net		209,110	226,201
Other assets		295,679	310,688
Total assets	[2]	12,751,358	13,982,904
Liabilities
Mortgages and other loans payable, net		1,961,240	2,837,282
Revolving credit facility, net		492,196	30,336
Unsecured term loans, net		1,493,051	1,491,575
Unsecured notes, net		1,495,214	1,395,939
Accrued interest payable		23,154	38,142
Other liabilities		116,566	188,005
Accounts payable and accrued expenses		147,060	137,142
Deferred revenue		94,453	208,119
Capital lease obligations		43,616	42,843
Deferred land leases payable		3,603	3,239
Dividend and distributions payable		80,430	85,138
Security deposits		64,688	67,927
Liabilities related to assets held for sale		0	4,074
Junior subordinated deferrable interest debentures held by trusts that issued trust preferred securities		100,000	100,000
Total liabilities	[2]	6,115,271	6,629,761
Limited partner interests in SLGOP (4,131 and 4,453 limited partner common units outstanding at December 31, 2018 and 2017, respectively)		387,805	461,954
Preferred units		300,427	301,735
Equity
Accumulated other comprehensive income		15,108	18,604
SL Green stockholders equity:
Series I Preferred Units, $25.00 liquidation preference, 9,200 issued and outstanding at both December 31, 2018 and 2017		221,932	221,932
SL Green partners' capital (878 and 973 general partner common units, and 82,806 and 91,831 limited partner common units outstanding at December 31, 2018 and 2017, respectively)		5,664,481	5,984,557
Total SLGOP partners' capital		5,901,521	6,225,093
Noncontrolling interests in other partnerships		46,334	364,361
Total capital		5,947,855	6,589,454
Total liabilities and equity/capital		$ 12,751,358	$ 13,982,904
[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: $110.0 million and $398.0 million of land, $0.3 billion and $1.4 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, $42.2 million and $330.9 million of accumulated depreciation, $721.3 million and $221.0 million of other assets included in other line items, $140.8 million and $628.9 million of real estate debt, net, $0.4 million and $2.5 million of accrued interest payable, $43.6 million and $42.8 million of capital lease obligations, and $18.4 million and $56.8 million of other liabilities included in other line items as of December 31, 2018 and December 31, 2017, 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: $110.0 million and $398.0 million of land, $0.3 billion and $1.4 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, $42.2 million and $330.9 million of accumulated depreciation, $721.3 million and $221.0 million of other assets included in other line items, $140.8 million and $628.9 million of real estate debt, net, $0.4 million and $2.5 million of accrued interest payable, $43.6 million and $42.8 million of capital lease obligations, and $18.4 million and $56.8 million of other liabilities included in other line items as of December 31, 2018 and December 31, 2017, respectively.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Tenant and other receivables, allowance	$ 15,702	$ 18,637
Deferred rents receivable, allowance	15,457	17,207
Discounts and deferred origination fees	22,379	25,507
Allowance for loan and lease losses	$ 5,750	$ 0
Preferred stock, par (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 25	$ 25
Preferred stock, shares issued (in shares)	9,200,000	9,200,000
Preferred stock, shares outstanding (in shares)	9,200,000	9,200,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	160,000,000	160,000,000
Common stock, shares issued (in shares)	84,739,000	93,858,000
Common stock, shares outstanding (in shares)	84,739,000	93,858,000
Treasury stock, shares (in shares)	1,055,000	1,055,000
Land	$ 1,774,899	$ 2,357,051
Building and improvements	5,268,484	6,351,012
Building leasehold and improvements	1,423,107	1,450,614
Properties under capital lease	47,445	47,445
Accumulated depreciation	2,099,137	2,300,116
Other assets	295,679	310,688
Real estate debt	1,961,240	2,837,282
Accrued interest payable	23,154	38,142
Capital lease obligations	43,616	42,843
Other liabilities	116,566	188,005
SL Green Operating Partnership
Tenant and other receivables, allowance	15,702	18,637
Deferred rents receivable, allowance	15,457	17,207
Discounts and deferred origination fees	22,379	$ 25,507
Allowance for loan and lease losses	$ 5,750
Limited partner interests in Operating Partnership, limited partner common units outstanding (shares)	4,131,000	4,453,000
Preferred units, liquidation preference (in dollars per share)	$ 25	$ 25
Preferred units, shares issued (in shares)	9,200,000	9,200,000
Preferred units, shares outstanding (in shares)	9,200,000	9,200,000
SL Green partner's capital, general partner common units outstanding (shares)	878,000	973,000
SL Green partners' capital, limited partner common units outstanding (shares)	82,806,000	91,831,000
Land	$ 1,774,899	$ 2,357,051
Building and improvements	5,268,484	6,351,012
Building leasehold and improvements	1,423,107	1,450,614
Properties under capital lease	47,445	47,445
Accumulated depreciation	2,099,137	2,300,116
Other assets	295,679	310,688
Real estate debt	1,961,240	2,837,282
Accrued interest payable	23,154	38,142
Capital lease obligations	43,616	42,843
Other liabilities	116,566	188,005
Consolidated VIEs
Land	110,000	398,000
Building and improvements	300,000	1,400,000
Building leasehold and improvements	2,000	2,000
Properties under capital lease	47,400	47,400
Accumulated depreciation	42,200	330,900
Other assets	721,300	221,000
Real estate debt	140,800	628,900
Accrued interest payable	400	2,500
Capital lease obligations	43,600	42,800
Other liabilities	$ 18,400	$ 56,800

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Rental revenue, net	$ 864,978,000	$ 1,100,993,000	$ 1,323,767,000
Escalation and reimbursement	113,596,000	172,939,000	196,858,000
Investment income	201,492,000	193,871,000	213,008,000
Other income	47,326,000	43,670,000	130,348,000
Total revenues	1,227,392,000	1,511,473,000	1,863,981,000
Expenses
Operating expenses, including $17,823 in 2018, $21,400 in 2017, $21,890 in 2016 of related party expenses	229,347,000	293,364,000	312,859,000
Real estate taxes	186,351,000	244,323,000	248,388,000
Ground rent	32,965,000	33,231,000	33,261,000
Interest expense, net of interest income	208,669,000	257,045,000	321,199,000
Amortization of deferred financing costs	12,408,000	16,498,000	24,564,000
Depreciation and amortization	279,507,000	403,320,000	821,041,000
Loan loss and other investment reserves, net of recoveries	6,839,000	0	0
Transaction related costs	1,099,000	(1,834,000)	7,528,000
Marketing, general and administrative	92,631,000	100,498,000	99,759,000
Total expenses	1,049,816,000	1,346,445,000	1,868,599,000
Equity in net income from unconsolidated joint ventures	7,311,000	21,892,000	11,874,000
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	303,967,000	16,166,000	44,009,000
Purchase price and other fair value adjustment	57,385,000	0	0
(Loss) gain on sale of real estate, net	(30,757,000)	73,241,000	238,116,000
Depreciable real estate reserves and impairment	(227,543,000)	(178,520,000)	(10,387,000)
Gain (loss) on sale of investment in marketable securities	0	3,262,000	(83,000)
Loss on early extinguishment of debt	(17,083,000)	0	0
Net income	270,856,000	101,069,000	278,911,000
Net (income) loss attributable to noncontrolling interests:
Noncontrolling interests in the Operating Partnership	(12,216,000)	(3,995,000)	(10,136,000)
Net (income) loss attributable to noncontrolling interests in other partnerships	6,000	15,701,000	(7,644,000)
Preferred unit distributions	(11,384,000)	(11,401,000)	(11,235,000)
Net income (loss) attributable to SL Green/SLGOP	247,262,000	101,374,000	249,896,000
Preferred stock/unit redemption costs	0	0	0
Perpetual preferred stock dividends	(14,950,000)	(14,950,000)	(14,950,000)
Net income attributable to SL Green common stockholders	$ 232,312,000	$ 86,424,000	$ 234,946,000
Basic weighted average common shares outstanding (in shares)	86,753	98,571	100,185
Diluted weighted average common shares and common share equivalents outstanding (in shares)	91,530	103,403	104,881
SL Green Operating Partnership
Revenues
Rental revenue, net	$ 864,978,000	$ 1,100,993,000	$ 1,323,767,000
Escalation and reimbursement	113,596,000	172,939,000	196,858,000
Investment income	201,492,000	193,871,000	213,008,000
Other income	47,326,000	43,670,000	130,348,000
Total revenues	1,227,392,000	1,511,473,000	1,863,981,000
Expenses
Operating expenses, including $17,823 in 2018, $21,400 in 2017, $21,890 in 2016 of related party expenses	229,347,000	293,364,000	312,859,000
Real estate taxes	186,351,000	244,323,000	248,388,000
Ground rent	32,965,000	33,231,000	33,261,000
Interest expense, net of interest income	208,669,000	257,045,000	321,199,000
Amortization of deferred financing costs	12,408,000	16,498,000	24,564,000
Depreciation and amortization	279,507,000	403,320,000	821,041,000
Loan loss and other investment reserves, net of recoveries	6,839,000	0	0
Transaction related costs	1,099,000	(1,834,000)	7,528,000
Marketing, general and administrative	92,631,000	100,498,000	99,759,000
Total expenses	1,049,816,000	1,346,445,000	1,868,599,000
Equity in net income from unconsolidated joint ventures	7,311,000	21,892,000	11,874,000
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	303,967,000	16,166,000	44,009,000
Purchase price and other fair value adjustment	57,385,000	0	0
(Loss) gain on sale of real estate, net	(30,757,000)	73,241,000	238,116,000
Depreciable real estate reserves and impairment	(227,543,000)	(178,520,000)	(10,387,000)
Gain (loss) on sale of investment in marketable securities	0	3,262,000	(83,000)
Loss on early extinguishment of debt	(17,083,000)	0	0
Net income	270,856,000	101,069,000	278,911,000
Net (income) loss attributable to noncontrolling interests:
Net (income) loss attributable to noncontrolling interests in other partnerships	6,000	15,701,000	(7,644,000)
Preferred unit distributions	(11,384,000)	(11,401,000)	(11,235,000)
Net income (loss) attributable to SL Green/SLGOP	259,478,000	105,369,000	260,032,000
Preferred stock/unit redemption costs	0	0	0
Perpetual preferred stock dividends	(14,950,000)	(14,950,000)	(14,950,000)
Net income attributable to SLGOP common unitholders	$ 244,528,000	$ 90,419,000	$ 245,082,000
Basic earnings per unit (in dollars per share)	$ 2.67	$ 0.87	$ 2.34
Diluted earnings per unit (in dollars per share)	$ 2.67	$ 0.87	$ 2.34
Basic weighted average common shares outstanding (in shares)	91,315	103,127	104,508
Basic weighted average common units outstanding (in shares)	91,315	103,127	104,508
Diluted weighted average common shares and common share equivalents outstanding (in shares)	91,530	103,403	104,881
Diluted weighted average common units and common unit equivalents outstanding (in shares)	91,530	103,403	104,881

Consolidated Statements of Op_2

Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses, paid to related parties	$ 17,823	$ 21,400	$ 21,890
SL Green Operating Partnership
Operating expenses, paid to related parties	$ 17,823	$ 21,400	$ 21,890

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net income	$ 270,856	$ 101,069	$ 278,911
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	(3,622)	1,040	28,508
Change in unrealized gain (loss) on marketable securities	60	(4,667)	3,677
Other comprehensive (loss) income	(3,562)	(3,627)	32,185
Comprehensive income	267,294	97,442	311,096
Net (income) loss attributable to noncontrolling interests and preferred units distributions	(23,594)	305	(29,015)
Net loss (income) attributable to noncontrolling interests	6	15,701	(7,644)
Other comprehensive income (loss) attributable to noncontrolling interests	66	94	(1,299)
Comprehensive income attributable to SL Green/SLGOP	243,766	97,841	280,782
SL Green Operating Partnership
Net income	270,856	101,069	278,911
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	(3,622)	1,040	28,508
Change in unrealized gain (loss) on marketable securities	60	(4,667)	3,677
Other comprehensive (loss) income	(3,562)	(3,627)	32,185
Comprehensive income	267,294	97,442	311,096
Net loss (income) attributable to noncontrolling interests	6	15,701	(7,644)
Other comprehensive income (loss) attributable to noncontrolling interests	66	94	(1,299)
Comprehensive income attributable to SL Green/SLGOP	$ 267,366	$ 113,237	$ 302,153

Consolidated Statement of Equit

Consolidated Statement of Equity - USD ($) $ 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, 2015	$ 7,719,317	$ 1,001	$ 5,439,735	$ (10,000)	$ (8,749)	$ 1,643,546	$ 431,852	$ 221,932
Beginning Balance (in shares) at Dec. 31, 2015		99,976,000
Increase (Decrease) in Stockholders' Equity
Net income (loss)	257,540					249,896	7,644
Other comprehensive income (loss)	30,886				30,886
Preferred dividends	(14,950)					(14,950)
DRSPP (in shares)		2,000
DRSPP proceeds	277		277
Conversion of units of the Operating Partnership to common stock (in shares)		295,000
Conversion of units in the Operating Partnership to common stock	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)		96,000
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	23,902	$ 1	23,901
Issuance of common stock (in shares)
Repurchases of common stock	(40)	$ 10	113,999	(114,049)
Proceeds from stock options exercised (in shares)		193,000
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 (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		100,562,000
Increase (Decrease) in Stockholders' Equity
Net income (loss)	85,673					101,374	(15,701)
Other comprehensive income (loss)	(3,533)				(3,533)
Preferred dividends	(14,950)					(14,950)
DRSPP (in shares)		2,000
DRSPP proceeds	223		223
Conversion of units of the Operating Partnership to common stock (in shares)		202,000
Conversion of units in the Operating Partnership to common stock	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)		87,000
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	$ 29,787	$ 1	29,786
Repurchases of common stock (in shares)	(8,342,411)	(8,342,000)
Repurchases of common stock	$ (848,048)	$ (83)	(621,324)			(226,641)
Proceeds from stock options exercised (in shares)		292,000
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 (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		92,803,000
Increase (Decrease) in Stockholders' Equity
Adjusted Balance	7,159,978	$ 939	4,968,338	(124,049)	18,604	1,709,853	364,361	221,932
Net income (loss)	247,256					247,262	(6)
Other comprehensive income (loss)	(3,496)				(3,496)
Preferred dividends	(14,950)					(14,950)
DRSPP (in shares)		1,000
DRSPP proceeds	136		136
Conversion of units of the Operating Partnership to common stock (in shares)		160,000
Conversion of units in the Operating Partnership to common stock	16,303	$ 2	16,301
Reallocation of noncontrolling interest in the Operating Partnership	34,236					34,236
Deferred compensation plan and stock award, net (in shares)		149,000
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	17,484	$ 1	17,483
Repurchases of common stock (in shares)		(9,745,000)
Repurchases of common stock	(937,795)	$ (98)	(522,482)			(415,215)
Proceeds from stock options exercised (in shares)		316,000
Proceeds from stock options exercised	28,912	$ 3	28,909
Contributions to consolidated joint venture interests	5,459						5,459
Deconsolidation of partially owned entity	(315,116)						(315,116)
Cash distributions to noncontrolling interests	(8,364)						(8,364)
Cash distributions declared (none of which represented a return of capital for federal income tax purposes)	(282,188)					(282,188)
Ending Balance at Dec. 31, 2018	$ 5,947,855	$ 847	$ 4,508,685	$ (124,049)	$ 15,108	$ 1,278,998	$ 46,334	$ 221,932
Ending Balance (in shares) at Dec. 31, 2018		83,684,000

Consolidated Statement of Equ_2

Consolidated Statement of Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Cash distribution declared, per common share (in dollars per share)	$ 3.2875	$ 3.1375	$ 2.94

Consolidated Statement of Capit

Consolidated Statement of Capital - USD ($) shares in Thousands, $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Increase (Decrease) in Partner's Capital
Preferred dividends	$ 838	$ (8,319)	$ (6,616)	$ 14,165
Conversion of common units					$ 16,303	$ 21,574	$ 31,806
DRSPP proceeds					136	223	277
Reallocation of noncontrolling interests in the operating partnership					34,236	5,712	(4,222)
Equity component of repurchased exchangeable senior notes						(109,776)
Proceeds from stock options exercised					28,912	23,314	14,832
Deconsolidation of partially owned entity					(315,116)	(30,203)
Cash distributions to noncontrolling interests					(8,364)	(52,446)	(15,419)
Common Stock
Increase (Decrease) in Partner's Capital
Conversion of common units					$ 2	$ 2	$ 3
DRSPP (in units)					1	2	2
DRSPP proceeds
Proceeds from stock options exercised (in shares)					316	292	193
Proceeds from stock options exercised					$ 3	$ 2	$ 2
Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Contributions to consolidated joint venture interests						36,275
Deconsolidation of partially owned entity					(315,116)	(30,203)
Cash distributions to noncontrolling interests					(8,364)	(52,446)	(15,419)
SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Beginning Balance		6,589,454		7,750,911	6,589,454	7,750,911	7,719,317
Adjusted Balance			7,159,978			7,159,978
Net income					247,256	85,673	257,540
Other comprehensive income (loss)					(3,496)	(3,533)	30,886
Preferred dividends	(2,601)	(3,047)	(5,328)	14,641	(14,950)	(14,950)	(14,950)
Conversion of common units					16,303	21,574	31,806
DRSPP proceeds					136	223	277
Reallocation of noncontrolling interests in the operating partnership					34,236	5,712	(4,222)
Equity component of repurchased exchangeable senior notes						(109,776)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings					17,484	29,787	23,902
Repurchases of common units					(937,795)	(848,048)
Proceeds from stock options exercised					28,912	23,314
Issuance of stock							(40)
Contributions to consolidated joint venture interests					5,459	36,275	2,359
Deconsolidation of partially owned entity					(315,116)	(30,203)
Proceeds from stock options exercised							14,832
Cash distributions to noncontrolling interests					(8,364)	(52,446)	(15,419)
Cash distributions declared (none of which represented a return of capital for federal income tax purposes)					(282,188)	(305,059)	(295,377)
Ending Balance	5,947,855		6,589,454		5,947,855	6,589,454	7,750,911
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
Adjusted Balance			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		$ 5,984,557		$ 7,080,406	$ 5,984,557	$ 7,080,406	$ 7,074,282
Beginning Balance (units)		92,803		100,562	92,803	100,562	99,976
Adjusted Balance			6,555,081			$ 6,555,081
Net income					$ 247,262	101,374	$ 249,896
Preferred dividends					$ (14,950)	$ (14,950)	$ (14,950)
Conversion of common units (in units)					160	202	295
Conversion of common units					$ 16,303	$ 21,574	$ 31,806
DRSPP (in units)					1		2
DRSPP proceeds					$ 136	223	$ 277
Reallocation of noncontrolling interests in the operating partnership					$ 34,236	5,712	$ (4,222)
Equity component of repurchased exchangeable senior notes						$ (109,776)
Deferred compensation plan and stock award, net, (in units)					149	87	96
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings					$ 17,484	$ 29,787	$ 23,902
Repurchases of common stock (in units)					(9,745)	(8,342)
Repurchases of common units					$ (937,795)	$ (848,048)
Proceeds from stock options exercised (in shares)					316	292
Proceeds from stock options exercised					$ 28,912	$ 23,314
Issuance of stock							$ (40)
Proceeds from stock options exercised (in units)							193
Proceeds from stock options exercised							$ 14,832
Cash distributions declared (none of which represented a return of capital for federal income tax purposes)					(282,188)	(305,059)	(295,377)
Ending Balance	$ 5,664,481		$ 5,984,557		$ 5,664,481	$ 5,984,557	$ 7,080,406
Ending Balance (units)	83,684		92,803		83,684	92,803	100,562
SL Green Operating Partnership | Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 18,604		$ 22,137	$ 18,604	$ 22,137	$ (8,749)
Adjusted Balance			$ 18,604			18,604
Other comprehensive income (loss)					(3,496)	(3,533)	30,886
Ending Balance	$ 15,108		18,604		15,108	18,604	22,137
SL Green Operating Partnership | Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 364,361		$ 426,436	364,361	426,436	431,852
Adjusted Balance			364,361			364,361
Net income					(6)	(15,701)	7,644
Contributions to consolidated joint venture interests					5,459		2,359
Deconsolidation of partially owned entity					(315,116)
Cash distributions to noncontrolling interests					(8,364)	(52,446)	(15,419)
Ending Balance	$ 46,334		$ 364,361		$ 46,334	$ 364,361	$ 426,436
Accounting Standards Update 2014-09
Increase (Decrease) in Partner's Capital
Cumulative adjustment upon adoption of ASC 610-20								$ 570,524
Accounting Standards Update 2014-09 | SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Cumulative adjustment upon adoption of ASC 610-20								570,524
Accounting Standards Update 2014-09 | SL Green Operating Partnership | Common Stock | Partners' Interest
Increase (Decrease) in Partner's Capital
Cumulative adjustment upon adoption of ASC 610-20								$ 570,524

Consolidated Statement of Cap_2

Consolidated Statement of Capital (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash distribution declared, per common share (in dollars per share)	$ 3.2875	$ 3.1375	$ 2.94
SL Green Operating Partnership
Cash distribution declared, per common share (in dollars per share)	$ 3.2875	$ 3.1375	$ 2.94

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Operating Activities
Net income		$ 270,856		$ 101,069	$ 278,911
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		291,915		419,818	845,605
Equity in net income from unconsolidated joint ventures		(7,311)		(21,892)	(11,874)
Distributions of cumulative earnings from unconsolidated joint ventures		10,277		20,309	24,337
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate		(303,967)		(16,166)	(44,009)
Purchase price and other fair value adjustment		(57,385)		0	0
Depreciable real estate reserves and impairment		227,543		178,520	10,387
Loss (gain) on sale of real estate, net		30,757		(73,241)	(238,116)
Loan loss reserves and other investment reserves, net of recoveries		6,839		0	0
(Gain) loss on sale of investments in marketable securities		0		(3,262)	83
Loss on early extinguishment of debt		17,083		0	0
Deferred rents receivable		(18,216)		(38,009)	26,716
Other non-cash adjustments	[1]	2,932		19,621	(152,428)
Changes in operating assets and liabilities:
Tenant and other receivables		6,968		(5,717)	4,780
Related party receivables		(1,044)		(7,209)	(5,183)
Deferred lease costs		(44,158)		(41,939)	(70,707)
Other assets		(8,310)		(23,068)	9,899
Accounts payable, accrued expenses and other liabilities and security deposits		4,410		(12,440)	(35,628)
Deferred revenue and land leases payable		12,348		46,607	1,237
Net cash provided by operating activities		441,537		543,001	644,010
Investing Activities
Acquisitions of real estate property		(60,486)		(28,680)	(39,890)
Additions to land, buildings and improvements		(254,460)		(336,001)	(411,950)
Investments in unconsolidated joint ventures		(400,429)		(389,249)	(145,375)
Distributions in excess of cumulative earnings from unconsolidated joint ventures		233,118		319,745	196,211
Proceeds from disposition of real estate/joint venture interest		1,231,004		692,796	2,475,954
Proceeds from sale of marketable securities		0		55,129	6,965
Purchases of marketable securities		0		0	(43,341)
Other investments		(38,912)		25,330	7,704
Origination of debt and preferred equity investments		(731,216)		(1,129,970)	(977,413)
Repayments or redemption of debt and preferred equity investments		703,043		812,914	904,517
Net cash provided by investing activities		681,662		22,014	1,973,382
Financing Activities
Proceeds from mortgages and other loans payable		564,391		870,459	408,293
Repayments of mortgages and other loans payable		(868,842)		(902,460)	(1,822,303)
Proceeds from revolving credit facility, term loans and senior unsecured notes		3,120,000		2,784,599	1,325,300
Repayments of revolving credit facility, term loans and senior unsecured notes		(2,560,000)		(2,276,782)	(2,334,604)
Payments of debt extinguishment costs		13,918		0	0
Proceeds from stock options exercised and DRSPP issuance		29,048		23,537	15,109
Repurchase of common stock		(979,541)		(806,302)	0
Redemption of preferred stock		(1,208)		(275)	(3,299)
Redemption of OP units		(33,972)		0	0
Distributions to noncontrolling interests in other partnerships		(8,364)		(52,446)	(15,419)
Contributions from noncontrolling interests in other partnerships		5,459		36,275	2,359
Distributions to noncontrolling interests in the Operating Partnership		(15,000)		(14,266)	(12,671)
Dividends/Distributions paid on common and preferred stock/units		(313,230)		(333,543)	(314,079)
Other obligations related to mortgage loan participations		16		17,227	59,150
Payment of tax witholdings for restricted share awards		(3,842)		(3,879)	(3,162)
Deferred loan costs and capitalized lease obligation		(15,109)		(27,100)	(41,076)
Net cash used in by financing activities		(1,094,112)		(684,956)	(2,736,402)
Net increase (decrease) in cash and cash equivalents		29,087		(119,941)	(119,010)
Cash, restricted cash, and cash equivalents at beginning of year		250,026		369,967
Cash, restricted cash, and cash equivalents at end of period		279,113		250,026	369,967
Supplemental Cash Flow Information [Abstract]
Interest paid		259,776		273,819	344,295
Income taxes paid		1,418		2,448	2,009
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the operating partnership		0		25,723	78,495
Redemption of units in the operating partnership		16,303		21,574	31,806
Redemption of units in the operating partnership for a joint venture sale		10,445		0	0
Exchange of debt investment for real estate or equity in joint venture		298,956		0	68,581
Tenant improvements and capital expenditures payable		0		6,667	15,972
Fair value adjustment to noncontrolling interest in operating partnership		34,236		5,712	4,222
Deconsolidation of a subsidiary	[2]	298,404		695,204	1,226,425
Transfer of assets to assets held for sale		0		611,809	2,048,376
Transfer of liabilities related to assets held for sale		0		5,364	1,677,528
Removal of fully depreciated commercial real estate properties		124,249		15,488	31,474
Issuance of SLG's common stock to a consolidated joint venture		0		0	114,049
Share repurchase payable		0		41,746	0
SL Green Operating Partnership
Operating Activities
Net income		270,856		101,069	278,911
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		291,915		419,818	845,605
Equity in net income from unconsolidated joint ventures		(7,311)		(21,892)	(11,874)
Distributions of cumulative earnings from unconsolidated joint ventures		10,277		20,309	24,337
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate		(303,967)		(16,166)	(44,009)
Purchase price and other fair value adjustment		(57,385)		0	0
Depreciable real estate reserves and impairment		227,543		178,520	10,387
Loss (gain) on sale of real estate, net		30,757		(73,241)	(238,116)
Loan loss reserves and other investment reserves, net of recoveries		6,839		0	0
(Gain) loss on sale of investments in marketable securities		0		(3,262)	83
Loss on early extinguishment of debt		17,083		0	0
Deferred rents receivable		(18,216)		(38,009)	26,716
Other non-cash adjustments		2,932	[1]	19,621	(152,428)
Changes in operating assets and liabilities:
Tenant and other receivables		6,968		(5,717)	4,780
Related party receivables		(1,044)		(7,209)	(5,183)
Deferred lease costs		(44,158)		(41,939)	(70,707)
Other assets		(8,310)		(23,068)	9,899
Accounts payable, accrued expenses and other liabilities and security deposits		4,410		(12,440)	(35,628)
Deferred revenue and land leases payable		12,348		46,607	1,237
Net cash provided by operating activities		441,537		543,001	644,010
Investing Activities
Acquisitions of real estate property		(60,486)		(28,680)	(39,890)
Additions to land, buildings and improvements		(254,460)		(336,001)	(411,950)
Investments in unconsolidated joint ventures		(400,429)		(389,249)	(145,375)
Distributions in excess of cumulative earnings from unconsolidated joint ventures		233,118		319,745	196,211
Proceeds from disposition of real estate/joint venture interest		1,231,004		692,796	2,475,954
Proceeds from sale of marketable securities		0		55,129	6,965
Purchases of marketable securities		0		0	(43,341)
Other investments		(38,912)		25,330	7,704
Origination of debt and preferred equity investments		(731,216)		(1,129,970)	(977,413)
Repayments or redemption of debt and preferred equity investments		703,043		812,914	904,517
Net cash provided by investing activities		681,662		22,014	1,973,382
Financing Activities
Proceeds from mortgages and other loans payable		564,391		870,459	408,293
Repayments of mortgages and other loans payable		(868,842)		(902,460)	(1,822,303)
Proceeds from revolving credit facility, term loans and senior unsecured notes		3,120,000		2,784,599	1,325,300
Repayments of revolving credit facility, term loans and senior unsecured notes		(2,560,000)		(2,276,782)	(2,334,604)
Payments of debt extinguishment costs		13,918		0	0
Proceeds from stock options exercised and DRSPP issuance		29,048		23,537	15,109
Repurchase of common stock		(979,541)		(806,302)	0
Redemption of preferred stock		(1,208)		(275)	(3,299)
Redemption of OP units		(33,972)		0	0
Distributions to noncontrolling interests in other partnerships		(8,364)		(52,446)	(15,419)
Contributions from noncontrolling interests in other partnerships		5,459		36,275	2,359
Dividends/Distributions paid on common and preferred stock/units		(328,230)		(347,809)	(326,750)
Other obligations related to mortgage loan participations		16		17,227	59,150
Payment of tax witholdings for restricted share awards		(3,842)		(3,879)	(3,162)
Deferred loan costs and capitalized lease obligation		(15,109)		(27,100)	(41,076)
Net cash used in by financing activities		(1,094,112)		(684,956)	(2,736,402)
Net increase (decrease) in cash and cash equivalents		29,087		(119,941)	(119,010)
Cash, restricted cash, and cash equivalents at beginning of year		250,026		369,967	488,977
Cash, restricted cash, and cash equivalents at end of period		279,113		250,026	369,967
Supplemental Cash Flow Information [Abstract]
Interest paid		259,776		273,819	344,295
Income taxes paid		1,418		2,448	2,009
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the operating partnership		0		25,723	78,495
Redemption of units in the operating partnership		16,303		21,574	31,806
Redemption of units in the operating partnership for a joint venture sale		10,445		0	0
Exchange of debt investment for real estate or equity in joint venture		298,956		0	68,581
Tenant improvements and capital expenditures payable		0		6,667	15,972
Fair value adjustment to noncontrolling interest in operating partnership		34,236		5,712	4,222
Deconsolidation of a subsidiary	[2]	298,404		695,204	1,226,425
Transfer of assets to assets held for sale		0		611,809	2,048,376
Transfer of liabilities related to assets held for sale		0		5,364	1,677,528
Removal of fully depreciated commercial real estate properties		124,249		15,488	31,474
Issuance of SLG's common stock to a consolidated joint venture		0		0	114,049
Share repurchase payable		0		41,746	0
Preferred Units
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition		0		0	22,793
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		$ 0	$ 22,793
[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 Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
		Nov. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly distributions declared, per share/unit (usd per share/unit)			$ 0.85	$ 0.8125	$ 0.775
Deconsolidation of a subsidiary	[1]		$ 298,404	$ 695,204	$ 1,226,425
SL Green Operating Partnership
Quarterly distributions declared, per share/unit (usd per share/unit)			$ 0.85	$ 0.8125	$ 0.775
Deconsolidation of a subsidiary	[1]		$ 298,404	$ 695,204	$ 1,226,425
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, 2018
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, 2018 , noncontrolling investors held, in the aggregate, a 4.70% 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, 2018 , 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 20 12,387,091 10 11,329,183 30 23,716,274 94.5 % Retail 7 (2) 325,648 9 352,174 16 677,822 96.7 % Development/Redevelopment 5 486,101 2 347,000 7 833,101 54.1 % Fee Interest — — 1 — 1 — — % 32 13,198,840 22 12,028,357 54 25,227,197 93.2 % Suburban Office 13 2,295,200 — — 13 2,295,200 91.3 % Retail 1 52,000 — — 1 52,000 100.0 % Development/Redevelopment 1 1,000 — — 1 1,000 — % 15 2,348,200 — — 15 2,348,200 91.4 % Total commercial properties 47 15,547,040 22 12,028,357 69 27,575,397 93.1 % Residential: Manhattan Residential 2 (2) 445,105 10 2,156,751 12 2,601,856 91.5 % Suburban Residential — — — — — — — % Total residential properties 2 445,105 10 2,156,751 12 2,601,856 91.5 % Total portfolio 49 15,992,145 32 14,185,108 81 30,177,253 92.9 % (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) As of December 31, 2018 , we owned a building at 315 West 33rd Street, also known as The Olivia, 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 this 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. As of December 31, 2018 , we also managed two office buildings owned by third parties encompassing approximately 2.1 million square feet (unaudited) and held debt and preferred equity investments with a book value of $2.1 billion , including $0.1 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 SL Green's common stock on a one-for- one basis.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
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 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. 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, 2018 , the weighted average amortization period for above-market leases, below-market leases, and in-place lease costs is 1.8 years, 4.6 years, and 5.8 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 $242.8 million , $365.3 million , and $783.5 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. On a periodic basis, we assess whether there are any indications that the value of our real estate properties may be 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. We recognized $6.8 million , $20.3 million , and $196.2 million of rental revenue for the years ended December 31, 2018 , 2017 , and 2016 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 $0.0 million , $0.8 million , and $2.8 million for the years ended December 31, 2018 , 2017 and 2016 , 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, 2018 and 2017 (in thousands): December 31, 2018 2017 Identified intangible assets (included in other assets): Gross amount $ 266,540 $ 325,880 Accumulated amortization (241,040 ) (277,038 ) Net (1) $ 25,500 $ 48,842 Identified intangible liabilities (included in deferred revenue): Gross amount $ 276,245 $ 540,283 Accumulated amortization (253,767 ) (402,583 ) Net (1) $ 22,478 $ 137,700 (1) As of December 31, 2018 , no net intangible assets and no net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale. 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): 2019 $ (5,227 ) 2020 (3,655 ) 2021 (1,631 ) 2022 (1,328 ) 2023 (749 ) 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): 2019 $ 9,825 2020 4,817 2021 3,454 2022 1,892 2023 1,507 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, 2018 , 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. The cost of marketable securities sold and the amount reclassified out of accumulated other comprehensive income into earnings is determined using the specific identification method. Any unrealized losses that are determined to be other-than-temporary are recognized in earnings up to their credit component. The Company adopted ASU 2016-01 effective January 1, 2018 which required entities to measure investments in equity securities at fair value and recognize any changes in fair value in net income. Upon adoption we did not hold investments in equity securities and therefore did not record a cumulative-effect adjustment. We did not hold investments in equity securities as of December 31, 2018 . At December 31, 2018 and 2017 , we held the following marketable securities (in thousands): December 31, 2018 2017 Commercial mortgage-backed securities $ 28,638 $ 28,579 Total marketable securities available-for-sale $ 28,638 $ 28,579 The cost basis of the commercial mortgage-backed securities was $27.5 million and $27.5 million at December 31, 2018 and 2017 , respectively. These securities mature at various times through 2035. We held no equity marketable securities at December 31, 2018 and 2017 . During the year ended December 31, 2018 , we did not dispose of any marketable securities. During the year ended December 31, 2017 , we disposed of marketable securities for aggregate net proceeds of $55.1 million and realized a loss 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 and includes adjustments related to basis differences that were identified as part of the initial accounting for the investment. 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 a master lease at one joint venture. 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, 2018 . 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, 2018 , 2017 and 2016 , $15.7 million , $16.4 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 financing 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 record a gain on sale of real estate assets when we no longer hold a controlling financial interest in the entity holding the real estate, a contract exists with a third party and that third party has control of the assets acquired. Investment 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. Allowance for Loan Loss and Other Investment Reserves The expense for loan loss and other investment reserves in connection with debt and preferred equity investments is the charge to earnings to adjust the allowance for possible losses to the level that we estimate to be adequate, based on Level 3 data, considering delinquencies, loss experience and collateral quality. The Company evaluates debt and preferred equity investments that are classified as held to maturity for possible impairment or credit deterioration associated with the performance and/or value of the underlying collateral property as well as the financial and operating capability of the borrower/sponsor. Quarterly, the Company assigns each loan a risk rating. Based on a 3-point scale, loans are rated “1” through “3,” from less risk to greater risk, which ratings are defined as follows: 1 - Low Risk Assets - Low probability of loss, 2 - Watch List Assets - Higher potential for loss, 3 - High Risk Assets - Loss more likely than not. When it is probable that we will be unable to collect all amounts contractually due, the investment is considered impaired. 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. Debt and preferred equity investments that are classified as 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. We have elected, and may elect in the future, to treat certain of our 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, 2018 , 2017 and 2016 , we recorded Federal, state and local tax provisions of $2.8 million , $4.3 million , and $2.8 million , respectively. For the year ended December 31, 2018 , the Company paid distributions on its common stock of $3.25 per share which represented $1.46 per share of ordinary income and $1.79 per share of capital gains. 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

Property Acquisitions

Property Acquisitions	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Property Acquisitions	Property Acquisitions 2018 Acquisitions During the year ended December 31, 2018 , the properties listed below were acquired from third parties. Property Acquisition Date Property Type Approximate Square Feet Acquisition Price (in millions) 2 Herald Square (1) May 2018 Leasehold Interest 369,000 $ 266.0 1231 Third Avenue (2)(3) July 2018 Fee Interest 39,000 55.4 Upper East Side Residential (3)(4) August 2018 Fee Interest 0.2 acres 30.2 133 Greene Street (2) October 2018 Fee Interest 6,425 31.0 712 Madison Avenue (2) December 2018 Fee Interest 6,600 58.0 (1) In May 2018, the Company was the successful bidder for the leasehold interest in 2 Herald Square, at the foreclosure of the asset. In April and May 2017, the Company had purchased, at par, loans in maturity default that were secured by the leasehold interest in 2 Herald Square. 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 believed that the fair value of the leasehold exceeded the carrying amount of the loans. In May 2018, the Company was the successful bidder at the foreclosure of the asset. We recorded the assets acquired and liabilities assumed at fair value. This resulted in the recognition of a fair value adjustment of $8.1 million , which is reflected in the Company's consolidated statement of operations within purchase price and other fair value adjustments. See Note 16, "Fair Value Measurements." The Company subsequently sold a 49% interest in the property in November 2018. See Note 4, "Properties Held for Sale and Dispositions." and Note 6, "Investments in Unconsolidated Joint Ventures." (2) The Company accepted an assignment of the equity interests in the property in lieu of repayment of the Company's debt investment, and recorded the assets received and liabilities assumed at fair value. (3) This property was subsequently sold in October 2018. See Note 4, "Properties Held for Sale and Dispositions." (4) In August 2018, the Company acquired the fee interest in three additional land parcels at the Upper East Side Residential Assemblage. 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 $ —

Properties Held for Sale and Pr

Properties Held for Sale and Property Dispositions	12 Months Ended
	Dec. 31, 2018
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, 2018 , no properties were classified as held for sale. Property Dispositions The following table summarizes the properties sold during the years ended December 31, 2018 , 2017 , and 2016 : Property Disposition Date Property Type Unaudited Approximate Usable Square Feet Sales Price (1) (in millions) Gain (Loss) on Sale (2) (in millions) 2 Herald Square (3) November 2018 Office/Retail 369,000 $ 265.0 $ — 400 Summit Lake Drive November 2018 Land 39.5 acres 3.0 (36.2 ) Upper East Side Assemblage (4)(5) October 2018 Development 70,142 143.8 (6.3 ) 1-6 International Drive July 2018 Office 540,000 55.0 (2.6 ) 635 Madison Avenue June 2018 Retail 176,530 153.0 (14.1 ) 115-117 Stevens Avenue May 2018 Office 178,000 12.0 (0.7 ) 600 Lexington Avenue January 2018 Office 303,515 305.0 23.8 1515 Broadway (6) December 2017 Office 1,750,000 1,950.0 — 125 Chubb Way 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 July 2017 Office 325,000 97.0 (44.2 ) 520 White Plains Road 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 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 (9) February 2016 Leased Fee Interest 607,000 453.0 (8.8 ) (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 600 Lexington, 16 Court Street, 102 Greene Street, 400 East 57th Street, 11 Madison Avenue, 388 Greenwich, and 248-252 Bedford Avenue are net of $1.3 million , $2.5 million , $0.9 million , $1.0 million , $0.6 million , $1.6 million , and $1.3 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 2018, the company sold a 49% interest in 2 Herald Square to an Israeli institutional investor. See Note 6, "Investments in Unconsolidated Joint Ventures." (4) Upper East Side Assemblage consists of 260 East 72nd Street, 31,076 square feet of development rights, 252-254 East 72nd Street, 257 East 71st Street, 259 East 71st Street, and 1231 Third Avenue. (5) The Company recorded a $5.8 million charge in 2018 that is included in depreciable real estate reserves and impairment in the consolidated statement of operations. (6) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. At that time, 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." (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. At that time, 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) In February 2016, we closed on the sale of 885 Third Avenue. At that time, 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.

Debt and Preferred Equity Inves

Debt and Preferred Equity Investments	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Debt and Preferred Equity Investments	Debt and Preferred Equity Investments Below is a summary of the activity relating to our debt and preferred equity investments as of December 31, 2018 and 2017 (in thousands): December 31, 2018 December 31, 2017 Balance at beginning of period (1) $ 2,114,041 $ 1,640,412 Debt investment originations/accretion (2) 834,304 1,142,591 Preferred equity investment originations/accretion (2) 151,704 144,456 Redemptions/sales/syndications/amortization (3) (994,906 ) (813,418 ) Net change in loan loss reserves (5,750 ) — Balance at end of period (1) $ 2,099,393 $ 2,114,041 (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 and are included in other assets and other liabilities on the consolidated balance sheets. The following table is a rollforward of our total loan loss reserves at December 31, 2018 , 2017 and 2016 (in thousands): December 31, 2018 2017 2016 Balance at beginning of year $ — $ — $ — Expensed 6,839 — — Recoveries — — — Charge-offs and reclassifications (1,089 ) — — Balance at end of period $ 5,750 $ — $ — At December 31, 2018 , all debt and preferred equity investments were performing in accordance with the terms of the relevant investments. At December 31, 2018 the Company's loan loss reserves of $5.8 million were attributable to two investments with an unpaid principal balance of $159.9 million that are being marketed for sale, are performing in accordance with their respective terms, and were not put on nonaccrual. At December 31, 2017 , all debt and preferred equity investments were performing in accordance with the terms of the relevant investments, with the exception of our investment in 2 Herald Square which was purchased in maturity default in May 2017 and April 2017, respectively, for which we subsequently were the successful bidder for the leasehold interest at the foreclosure of the asset as discussed in Note 3, "Property Acquisitions," and a junior mortgage participation acquired in September 2014, which was acquired for zero , had a carrying value of zero and was canceled in 2018. We have determined that we have one portfolio segment of financing receivables at December 31, 2018 and 2017 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 $88.8 million and $65.5 million at December 31, 2018 and 2017 , respectively. No financing receivables were 90 days past due at December 31, 2018 with the exception of a $28.4 million financing receivable which was put on nonaccrual in August as a result of interest default. The loan was evaluated in accordance with our loan review procedures and the Company concluded that the fair value of the collateral exceeded the carrying amount of the loan. As of December 31, 2018 , Management estimated the weighted average risk rating for our debt and preferred equity investments to be 1.2 . Debt Investments As of December 31, 2018 and 2017 , we held the following debt investments with an aggregate weighted average current yield of 8.99% , at December 31, 2018 (in thousands): Loan Type December 31, 2018 Future Funding Obligations December 31, 2018 Senior Financing December 31, 2018 Carrying Value (1) December 31, 2017 Carrying Value (1) Maturity Date (2) Fixed Rate Investments: Mezzanine Loan (3a) $ — $ 1,160,000 $ 213,185 $ 204,005 March 2020 Mezzanine Loan — 15,000 3,500 3,500 September 2021 Mezzanine Loan — 147,000 24,932 24,913 April 2022 Mezzanine Loan — 280,000 36,585 34,600 August 2022 Mezzanine Loan — 85,097 12,706 12,699 November 2023 Mezzanine Loan — 180,000 30,000 — December 2023 Mezzanine Loan (3b) — 115,000 12,941 12,932 June 2024 Mezzanine Loan — 95,000 30,000 30,000 January 2025 Mezzanine Loan — 340,000 11,000 15,000 November 2026 Mezzanine Loan — 1,712,750 55,250 55,250 June 2027 Mortgage/Jr. Mortgage Loan (4) — — — 250,464 Mortgage Loan (5) — — — 26,366 Mortgage Loan (5) — — — 239 Total fixed rate $ — $ 4,129,847 $ 430,099 $ 669,968 Floating Rate Investments: Mezzanine Loan (6) $ — $ 45,025 $ 37,499 $ 34,879 January 2019 Mezzanine Loan (3c)(7) — 85,000 15,333 15,381 March 2019 Mezzanine Loan (3d)(7) — 65,000 14,822 14,869 March 2019 Mezzanine Loan (8) — 38,000 21,990 21,939 March 2019 Mezzanine Loan (7) — 40,000 19,986 19,982 April 2019 Mezzanine Loan — 265,000 24,961 24,830 April 2019 Mortgage/Jr. Mortgage Participation Loan 40,530 233,086 84,012 71,832 August 2019 Mezzanine Loan (7)(8) — 65,000 14,998 14,955 August 2019 Mortgage/Mezzanine Loan (7) — — 19,999 19,940 August 2019 Mortgage/Mezzanine Loan 1,027 — 154,070 143,919 September 2019 Mezzanine Loan — 350,000 34,886 34,737 October 2019 Mortgage/Mezzanine Loan (9) 7,243 — 62,493 43,845 January 2020 Mezzanine Loan (9) 559 575,955 79,164 75,834 January 2020 Mortgage Loan 11,204 — 88,501 — February 2020 Mezzanine Loan 1,277 322,300 53,402 — March 2020 Mortgage/Mezzanine Loan 14,860 — 277,694 — April 2020 Mortgage/Mezzanine Loan (7) — — 37,094 — June 2020 Mezzanine Loan 7,887 38,167 12,627 11,259 July 2020 Mortgage/Mezzanine Loan — — 83,449 — October 2020 Mezzanine Loan 38,575 362,908 88,817 75,428 November 2020 Mortgage/Mezzanine Loan 33,131 — 98,804 88,989 December 2020 Mortgage/Mezzanine Loan — — 35,266 35,152 December 2020 Jr. Mortgage Participation/Mezzanine Loan — 60,000 15,665 15,635 July 2021 Mezzanine Loan (8) — 38,596 7,305 34,947 December 2021 Mortgage/Mezzanine Loan (5) — — — 162,553 Mortgage/Mezzanine Loan (5) — — — 74,755 Mortgage/Mezzanine Loan (10) — — — 23,609 Loan Type December 31, 2018 Future Funding Obligations December 31, 2018 Senior Financing December 31, 2018 Carrying Value (1) December 31, 2017 Carrying Value (1) Maturity Date (2) Mortgage/Mezzanine Loan (5) — — — 16,969 Mezzanine Loan (5) — — — 59,723 Mezzanine Loan (5) — — — 37,851 Mezzanine Loan (5) — — — 14,855 Mezzanine Loan (11) — — — 12,174 Mezzanine Loan (11) — — — 10,934 Mezzanine Loan (5) — — — 37,250 Mezzanine Loan (5) — — — 15,148 Mezzanine Loan (5) — — — 8,550 Mezzanine Loan (11) — — — 26,927 Total floating rate $ 156,293 $ 2,584,037 $ 1,382,837 $ 1,299,650 Total $ 156,293 $ 6,713,884 $ 1,812,936 $ 1,969,618 (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) 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) $1.3 million , (b) $12.0 million , (c) $14.6 million , and (d) $14.1 million . (4) 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 believed that the fair value of the property exceeded the carrying amount of the loans. In May 2018, the Company was the successful bidder at the foreclosure of the asset, at which time the loans were credited to our equity investment in the property. (5) This loan was repaid in 2018. (6) As of January 2019, this loan is in maturity default. No impairment was recorded as the Company believes that the fair value of the property exceeded the carrying amount of the loans. (7) This loan was extended in 2018. (8) This loan was repaid in 2019. (9) This loan was modified in 2019. (10) This loan was sold in 2018. (11) In 2018, the Company accepted an assignment of the equity interests in the property in lieu of repayment of the loan, and recorded the assets received and liabilities assumed at fair value. Preferred Equity Investments As of December 31, 2018 and 2017 , we held the following preferred equity investments with an aggregate weighted average current yield of 9.12% at December 31, 2018 (in thousands): Type December 31, 2018 Future Funding Obligations December 31, 2018 December 31, 2018 (1) December 31, 2017 (1) Mandatory Redemption (2) Preferred Equity (3) $ — $ 272,000 $ 143,183 $ 144,423 April 2021 Preferred Equity — 1,768,000 143,274 — June 2022 $ — $ 2,040,000 $ 286,457 $ 144,423 (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.

Investments in Unconsolidated J

Investments in Unconsolidated Joint Ventures	12 Months Ended
	Dec. 31, 2018
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, 2018 , the book value of these investments was $3.0 billion , net of investments with negative book values totaling $85.8 million for which we have an implicit commitment to fund future capital needs. As of December 31, 2018 and 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 $808.3 million as of December 31, 2018 and $606.2 million as of December 31, 2017 . 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, 2018 : 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 285,000 919 Third Avenue (3) New York State Teacher's Retirement System 51.00% 51.00% 1,454,000 January 2007 1,256,727 11 West 34th Street Private Investor/ Jeff Sutton 30.00% 30.00% 17,150 December 2010 10,800 280 Park Avenue Vornado Realty Trust 50.00% 50.00% 1,219,158 March 2011 400,000 1552-1560 Broadway (4) Jeff Sutton 50.00% 50.00% 57,718 August 2011 136,550 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 (5) Private Investors 32.28% 32.28% 13,069 December 2012 75,000 650 Fifth Avenue (6) 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 55 West 46th Street Prudential Real Estate Investors 25.00% 25.00% 347,000 November 2014 295,000 Stonehenge Portfolio (7) Various Various Various 1,439,016 February 2015 36,668 131-137 Spring Street (8) 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 Private Investors 33.33% 33.33% 26,926 August 2016 — 400 East 57th Street (9) BlackRock, Inc and Stonehenge Partners 51.00% 41.00% 290,482 October 2016 170,000 One Vanderbilt (10) National Pension Service of Korea/Hines Interest LP 71.01% 71.01% — January 2017 3,310,000 Worldwide Plaza RXR Realty / New York REIT / Private Investor 24.35% 24.35% 2,048,725 October 2017 1,725,000 1515 Broadway (11) Allianz Real Estate of America 56.87% 56.87% 1,750,000 November 2017 1,950,000 2 Herald Square Israeli Institutional Investor 51.00% 51.00% 369,000 November 2018 266,000 (1) Ownership interest and economic interest represent the Company's interests in the joint venture as of December 31, 2018 . 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) In January 2018, the partnership agreement for our investment was modified resulting in the Company no longer having a controlling interest in this investment. As a result the investment was deconsolidated as of January 1, 2018. The Company recorded its non-controlling interest at fair value resulting in a $49.3 million fair value adjustment in the consolidated statement of operations. This fair value was allocated to the assets and liabilities, including identified intangibles of the property. (4) 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. (5) 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. (6) 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. (7) In February and March 2018, the Company, together with its joint venture partner, closed on the sale of two properties from the Stonehenge Portfolio. These sales are further described under Sale of Joint Venture Interest of Properties below. (8) In January 2019, we closed on the sale of our interest in this property to our joint venture partner. The transaction generated net cash proceeds to the Company of $15.2 million . (9) In October 2016, the Company sold a 49% interest in this property to an investment account managed by 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. (10) 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, 2018 the total of the two partners' ownership interests based on equity contributed was 23.4% . (11) In November 2017, the Company sold a 30% 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. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and recorded a $0.6 billion gain from the sale of the partial interest and related step-up in basis to fair value of the retained non-controlling interest as an adjustment to beginning retained earnings based on the application of the modified retrospective adoption approach. The Company closed on the sale of an additional 13% 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, 2018 and 2017 , the carrying value for acquisition, development and construction arrangements were as follows (in thousands): Loan Type December 31, 2018 December 31, 2017 Maturity Date Mezzanine Loan (1) $ 44,357 44,823 February 2022 Mezzanine Loan and Preferred Equity (2) — 100,000 Mezzanine Loan (3) — 26,716 $ 44,357 $ 171,539 (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 mezzanine loan was repaid and the preferred equity interest was redeemed in March 2018. (3) The Company was redeemed on this investment in July 2018. Disposition of Joint Venture Interests or Properties The following table summarizes the investments in unconsolidated joint ventures sold during the years ended December 31, 2018 , 2017 , and 2016 : Property Ownership Interest Sold Disposition Date Type of Sale Gross Asset Valuation (in thousands) (1) Gain (Loss) on Sale (in thousands) (2) 3 Columbus Circle 48.90% November 2018 Ownership Interest $ 851,000 $ 160,368 Mezzanine Loan (3) 33.33% August 2018 Repayment 15,000 N/A 724 Fifth Avenue 49.90% July 2018 Ownership Interest 365,000 64,587 Jericho Plaza (4) 11.67% June 2018 Ownership Interest 117,400 147 1745 Broadway 56.87% May 2018 Property 633,000 52,038 175-225 Third Street Brooklyn, New York 95.00% April 2018 Property 115,000 19,483 Stonehenge Village (5) 0.50% March 2018 Property 287,000 (5,701 ) 1515 Broadway (6) 13.00% February 2018 Ownership Interest 1,950,000 — 1274 Fifth Avenue (5) 9.83% February 2018 Property 44,100 (362 ) 102 Greene Street 10.00% September 2017 Ownership Interest 43,500 283 76 11th Avenue (7) 33.33% May 2017 Repayment 138,240 N/A Stonehenge Portfolio (partial) (6) Various March 2017 Ownership Interest 300,000 871 EOP Denver 0.48% September 2016 Ownership Interest 180,700 300 33 Beekman (8) 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 Jericho Plaza (4) 66.11% February 2016 Ownership Interest 95,200 3,300 (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 $11.7 million , $0 , and $1.1 million of employee compensation accrued in connection with the realization of these investment gains in the years ended December 31, 2018 , 2017 , and 2016 , respectively. Additionally, gain (loss) amounts do not include adjustments for expenses recorded in subsequent periods. (3) Our investment in a joint venture that owned a mezzanine loan secured by a commercial property in midtown Manhattan was repaid after the joint venture received repayment of the underlying loan. (4) We sold our 11.67 % interest in June 2018. In the first quarter of 2016, our ownership percentage was reduced from 77.78 % to 11.67 %, upon completion of a restructuring of the joint venture. (5) Properties were part of the Stonehenge Portfolio. (6) Our investment in 1515 Broadway was marked to fair value on January 1, 2018 upon adoption of ASC 610-20. (7) 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. (8) In connection with the sale of the property, we also recognized a promote of $10.8 million . 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 may provide 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, 2018 and 2017 , respectively, are as follows (amounts in thousands): Property Economic Interest (1) Maturity Date Interest Rate (2) December 31, 2018 December 31, 2017 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% 210,000 210,000 650 Fifth Avenue (4) 50.00 % October 2022 5.45% 65,000 65,000 21 East 66th Street 32.28 % April 2023 3.60% 12,000 12,000 919 Third Avenue 51.00 % June 2023 5.12% 500,000 — 1515 Broadway 56.87 % March 2025 3.93% 855,876 872,528 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% 99,828 100,000 Worldwide Plaza 24.35 % November 2027 3.98% 1,200,000 1,200,000 Stonehenge Portfolio (5) Various Various 4.20% 321,076 357,282 3 Columbus Circle (6) — 350,000 Total fixed rate debt $ 5,666,108 $ 5,569,138 Floating Rate Debt: 280 Park Avenue 50.00 % September 2019 L+ 1.73% $ 1,200,000 $ 1,200,000 121 Greene Street 50.00 % November 2019 L+ 1.50% 15,000 15,000 10 East 53rd Street 55.00 % February 2020 L+ 2.25% 170,000 170,000 131-137 Spring Street (7) 20.00 % August 2020 L+ 1.55% 141,000 141,000 1552 Broadway 50.00 % October 2020 L+ 2.65% 195,000 195,000 55 West 46th Street (8) 25.00 % November 2020 L+ 2.13% 185,569 171,444 11 West 34th Street 30.00 % January 2021 L+ 1.45% 23,000 23,000 103 East 86th Street (9) 1.00 % January 2021 L+ 1.40% 38,000 55,340 100 Park Avenue 49.90 % February 2021 L+ 1.75% 360,000 360,000 One Vanderbilt (10) 71.01 % September 2021 L+ 2.75% 375,000 355,535 2 Herald Square (11) 51.00 % November 2021 L+ 1.55% 133,565 — 605 West 42nd Street 20.00 % August 2027 L+ 1.44% 550,000 550,000 21 East 66th Street 32.28 % June 2033 1 Year Treasury+ 2.75% 1,571 1,648 175-225 Third Street Brooklyn, New York (12) — 40,000 1745 Broadway (12) — 345,000 Jericho Plaza (13) — 81,099 724 Fifth Avenue (14) — 275,000 Total floating rate debt $ 3,387,705 $ 3,979,066 Total joint venture mortgages and other loans payable $ 9,053,813 $ 9,548,204 Deferred financing costs, net (103,191 ) (136,103 ) Total joint venture mortgages and other loans payable, net $ 8,950,622 $ 9,412,101 (1) Economic interest represents the Company's interests in the joint venture as of December 31, 2018 . Changes in ownership or economic interests, if any, within the current year are disclosed in the notes to the investment in unconsolidated joint ventures table above. (2) Interest rate as of December 31, 2018 , 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) These loans are comprised of a $210.0 million fixed rate mortgage loan and $65.0 million fixed rate mezzanine loan. (5) Amount is comprised of $134.3 million , $54.1 million , and $132.6 million in fixed-rated mortgages that mature in August 2019, June 2024, and April 2028, respectively. (6) In November 2018, we closed on the sale of our interest in the property to our joint venture partner. (7) In January 2019, we closed on the sale of our interest in this property to our joint venture partner. (8) This loan has a committed amount of $195.0 million , of which $9.4 million was unfunded as of December 31, 2018 . (9) In February 2019, along with our joint venture partner, we closed on the sale of the property. (10) This loan is a $1.75 billion construction facility, with reductions in interest cost 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) This loan has a committed amount of $150.0 million . (12) In 2018, along with our joint venture partner, we closed on the sale of the property. (13) In 2018, we closed on the sale of our interest in the property. (14) In 2018, we closed on the sale of substantially all of our interest in the property to our joint venture partner. We act as the operating partner and day-to-day manager for all our joint ventures, except for Worldwide Plaza, 800 Third Avenue, 280 Park Avenue, 21 East 66th 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 $14.2 million , $22.6 million and $4.0 million from these services, net of our ownership share of the joint ventures, for the years ended December 31, 2018 , 2017 , and 2016 , 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, 2018 and 2017 , are as follows (in thousands): December 31, 2018 December 31, 2017 Assets (1) Commercial real estate property, net $ 14,347,673 $ 12,822,133 Cash and restricted cash 381,301 494,909 Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance 273,141 349,944 Debt and preferred equity investments, net 44,357 202,539 Other assets 2,187,166 1,407,806 Total assets $ 17,233,638 $ 15,277,331 Liabilities and equity (1) Mortgages and other loans payable, net $ 8,950,622 $ 9,412,101 Deferred revenue/gain 1,660,838 985,648 Other liabilities 946,313 411,053 Equity 5,675,865 4,468,529 Total liabilities and equity $ 17,233,638 $ 15,277,331 Company's investments in unconsolidated joint ventures $ 3,019,020 $ 2,362,989 (1) The combined assets, liabilities and equity for the unconsolidated joint ventures reflects the effect of step ups in basis on the retained non-controlling interests in deconsolidated investments as a result of the adoption of ASC 610-20 in January 2018. The combined statements of operations for the unconsolidated joint ventures, from acquisition date through the years ended December 31, 2018 , 2017 , and 2016 are as follows (in thousands): Year Ended December 31, 2018 2017 2016 Total revenues $ 1,244,804 $ 904,230 $ 712,689 Operating expenses 219,440 157,610 126,913 Real estate taxes 226,961 142,774 111,673 Ground rent 18,697 16,794 14,924 Interest expense, net of interest income 363,055 250,063 197,741 Amortization of deferred financing costs 21,634 23,026 24,829 Transaction related costs — 146 5,566 Depreciation and amortization 421,458 279,419 199,011 Total expenses $ 1,271,245 $ 869,832 $ 680,657 Loss on early extinguishment of debt — (7,899 ) (1,606 ) Net (loss) income before gain on sale (1) $ (26,441 ) $ 26,499 $ 30,426 Company's equity in net income from unconsolidated joint ventures (1) $ 7,311 $ 21,892 $ 11,874 (1) The combined statements of operations and the Company's equity in net income for the unconsolidated joint ventures reflects the effect of step ups in basis on the retained non-controlling interests in deconsolidated investments as a result of the adoption of ASC 610-20 in January 2018.

Deferred Costs

Deferred Costs	12 Months Ended
	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred Costs	Deferred Costs Deferred costs at December 31, 2018 and 2017 consisted of the following (in thousands): December 31, 2018 2017 Deferred leasing costs $ 453,833 $ 443,341 Less: accumulated amortization (244,723 ) (217,140 ) Deferred costs, net $ 209,110 $ 226,201

Mortgages and Other Loans Payab

Mortgages and Other Loans Payable	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) December 31, 2018 December 31, 2017 Fixed Rate Debt: 762 Madison Avenue February 2022 5.00% 771 771 100 Church Street July 2022 4.68% 213,208 217,273 420 Lexington Avenue October 2024 3.99% 300,000 300,000 400 East 58th Street (2) November 2026 3.00% 39,931 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 (3) February 2027 3.58% 35,807 36,363 315 West 33rd Street February 2027 4.17% 250,000 250,000 919 Third Avenue (4) — 500,000 Unsecured Loan (5) — 16,000 Series J Preferred Units (6) — 4,000 One Madison Avenue (7) — 486,153 Total fixed rate debt $ 1,389,717 $ 2,400,560 Floating Rate Debt: FHLB Facility May 2019 L+ 0.27% $ 13,000 $ — 2017 Master Repurchase Agreement June 2019 L+ 2.34% 300,000 90,809 FHLB Facility December 2019 L+ 0.18% 14,500 — 133 Greene Street August 2020 L+ 2.00% 15,523 — 185 Broadway (8) November 2021 L+ 2.85% 111,869 58,000 712 Madison December 2021 L+ 2.50% 28,000 — 115 Spring Street September 2023 L+ 3.40% 65,550 — 719 Seventh Avenue September 2023 L+ 1.20% 50,000 41,622 220 East 42nd Street (9) — 275,000 Total floating rate debt $ 598,442 $ 465,431 Total fixed rate and floating rate debt $ 1,988,159 $ 2,865,991 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 1,988,159 $ 2,865,991 Deferred financing costs, net of amortization (26,919 ) (28,709 ) Total mortgages and other loans payable, net $ 1,961,240 $ 2,837,282 (1) Interest rate as of December 31, 2018 , 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) 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 . (3) 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 . (4) Our investment in the property was deconsolidated as of January 1, 2018. See Note 6, "Investments in Unconsolidated Joint Ventures". (5) In May 2018, the loan was repaid in connection with the sale of the property. (6) In June 2018, the Series J Preferred Units were redeemed in connection with the sale of the property. (7) In 2018, the Company recognized a $14.9 million loss on extinguishment of debt related to the early repayment of this loan. (8) This loan is a $225.0 million construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial three -year term with two one -year extension options. Advances under the loan are subject to incurred costs and funded equity requirements. (9) In 2018, the mortgage was repaid. At December 31, 2018 and 2017 , 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 $3.9 billion and $4.8 billion , respectively. Federal Home Loan Bank of New York Facility The Company’s wholly-owned subsidiary, Ticonderoga Insurance Company, or Ticonderoga, a Vermont licensed captive insurance company, is a member of the Federal Home Loan Bank of New York, or FHLBNY. As a member, Ticonderoga may borrow funds from the FHLBNY in the form of secured advances. As of December 31, 2018 , we had $13.0 million and $14.5 million in outstanding secured advances with a borrowing rate of 30-day LIBOR over 27 basis points and 30-day LIBOR over 18 basis points, respectively. 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 . In April 2018, we increased the maximum facility capacity to $400.0 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. In June 2018, we exercised a one year extension option. At December 31, 2018 , the facility had a carrying value of $299.6 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 . In June 2018, we terminated the restated 2016 MRA. The facility bore interest ranging from 225 and 400 basis points over 30-day LIBOR depending on the pledged collateral and had an initial two -year term, with a one year extension option. Since December 6, 2015, we had 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 was less than $150.0 million . 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, 2018 , 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, 2018 , 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, 2018 , 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, 2018 , the facility fee was 20 basis points. As of December 31, 2018 , we had $11.8 million of outstanding letters of credit, $500.0 million drawn under the revolving credit facility and $1.5 billion outstanding under the term loan facilities, with total undrawn capacity of $1.0 billion under the 2017 credit facility. At December 31, 2018 and December 31, 2017 , the revolving credit facility had a carrying value of $492.2 million and $30.3 million , respectively, net of deferred financing costs. At December 31, 2018 and December 31, 2017 , the term loan facilities had a carrying value of $1.5 billion and $1.5 billion , respectively, net of deferred financing costs. The Company and the Operating Partnership are borrowers jointly and severally obligated 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, 2018 and 2017 , respectively, by scheduled maturity date (amounts in thousands): Issuance December 31, 2018 Unpaid Principal Balance December 31, 2018 Accreted Balance December 31, 2017 Accreted Balance Interest Rate (1) Initial Term (in Years) Maturity Date March 16, 2010 (2) $ 250,000 $ 250,000 $ 250,000 7.75 % 10 March 2020 August 7, 2018 (3) (4) 350,000 350,000 — L+ 0.98 % 3 August 2021 October 5, 2017 (3) 500,000 499,591 499,489 3.25 % 5 October 2022 November 15, 2012 (5) 300,000 304,168 305,163 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 August 5, 2011 (2) (6) — — 249,953 $ 1,500,000 $ 1,503,759 $ 1,404,605 Deferred financing costs, net (8,545 ) (8,666 ) $ 1,500,000 $ 1,495,214 $ 1,395,939 (1) Interest rate as of December 31, 2018 , taking into account interest rate hedges in effect during the period. Floating rate notes are presented with the stated spread over 3-month LIBOR, unless otherwise specified. 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 and the Operating Partnership as co-obligors. (3) Issued by the Operating Partnership with the Company as the guarantor. (4) Beginning on August 8, 2019 and at any time thereafter, the notes are subject to redemption at the Company's option, in whole but not in part, at a redemption price equal to 100% of the principal amount of the notes, plus unpaid accrued interest thereon to the redemption date. (5) In October 2017, the Company and the Operating Partnership 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% . (6) The balance was repaid in August 2018. 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, 2018 and 2017 , 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, 2018 , 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 2019 $ 6,241 $ 27,500 $ — $ — $ — $ — $ 33,741 $ 115,295 2020 11,117 315,523 — — — 250,000 576,640 278,791 2021 11,636 139,869 — — — 350,000 501,505 518,371 2022 9,429 198,588 — — — 800,000 1,008,017 220,810 2023 7,301 115,550 500,000 1,300,000 — — 1,922,851 277,996 Thereafter 9,290 1,136,115 — 200,000 100,000 100,000 1,545,405 2,430,198 $ 55,014 $ 1,933,145 $ 500,000 $ 1,500,000 $ 100,000 $ 1,500,000 $ 5,588,159 $ 3,841,461 Consolidated interest expense, excluding capitalized interest, was comprised of the following (in thousands): Year Ended December 31, 2018 2017 2016 Interest expense before capitalized interest $ 244,788 $ 284,649 $ 348,062 Interest capitalized (34,162 ) (26,020 ) (24,067 ) Interest income (1,957 ) (1,584 ) (2,796 ) Interest expense, net $ 208,669 $ 257,045 $ 321,199

Corporate Indebtedness

Corporate Indebtedness	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) December 31, 2018 December 31, 2017 Fixed Rate Debt: 762 Madison Avenue February 2022 5.00% 771 771 100 Church Street July 2022 4.68% 213,208 217,273 420 Lexington Avenue October 2024 3.99% 300,000 300,000 400 East 58th Street (2) November 2026 3.00% 39,931 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 (3) February 2027 3.58% 35,807 36,363 315 West 33rd Street February 2027 4.17% 250,000 250,000 919 Third Avenue (4) — 500,000 Unsecured Loan (5) — 16,000 Series J Preferred Units (6) — 4,000 One Madison Avenue (7) — 486,153 Total fixed rate debt $ 1,389,717 $ 2,400,560 Floating Rate Debt: FHLB Facility May 2019 L+ 0.27% $ 13,000 $ — 2017 Master Repurchase Agreement June 2019 L+ 2.34% 300,000 90,809 FHLB Facility December 2019 L+ 0.18% 14,500 — 133 Greene Street August 2020 L+ 2.00% 15,523 — 185 Broadway (8) November 2021 L+ 2.85% 111,869 58,000 712 Madison December 2021 L+ 2.50% 28,000 — 115 Spring Street September 2023 L+ 3.40% 65,550 — 719 Seventh Avenue September 2023 L+ 1.20% 50,000 41,622 220 East 42nd Street (9) — 275,000 Total floating rate debt $ 598,442 $ 465,431 Total fixed rate and floating rate debt $ 1,988,159 $ 2,865,991 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 1,988,159 $ 2,865,991 Deferred financing costs, net of amortization (26,919 ) (28,709 ) Total mortgages and other loans payable, net $ 1,961,240 $ 2,837,282 (1) Interest rate as of December 31, 2018 , 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) 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 . (3) 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 . (4) Our investment in the property was deconsolidated as of January 1, 2018. See Note 6, "Investments in Unconsolidated Joint Ventures". (5) In May 2018, the loan was repaid in connection with the sale of the property. (6) In June 2018, the Series J Preferred Units were redeemed in connection with the sale of the property. (7) In 2018, the Company recognized a $14.9 million loss on extinguishment of debt related to the early repayment of this loan. (8) This loan is a $225.0 million construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial three -year term with two one -year extension options. Advances under the loan are subject to incurred costs and funded equity requirements. (9) In 2018, the mortgage was repaid. At December 31, 2018 and 2017 , 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 $3.9 billion and $4.8 billion , respectively. Federal Home Loan Bank of New York Facility The Company’s wholly-owned subsidiary, Ticonderoga Insurance Company, or Ticonderoga, a Vermont licensed captive insurance company, is a member of the Federal Home Loan Bank of New York, or FHLBNY. As a member, Ticonderoga may borrow funds from the FHLBNY in the form of secured advances. As of December 31, 2018 , we had $13.0 million and $14.5 million in outstanding secured advances with a borrowing rate of 30-day LIBOR over 27 basis points and 30-day LIBOR over 18 basis points, respectively. 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 . In April 2018, we increased the maximum facility capacity to $400.0 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. In June 2018, we exercised a one year extension option. At December 31, 2018 , the facility had a carrying value of $299.6 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 . In June 2018, we terminated the restated 2016 MRA. The facility bore interest ranging from 225 and 400 basis points over 30-day LIBOR depending on the pledged collateral and had an initial two -year term, with a one year extension option. Since December 6, 2015, we had 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 was less than $150.0 million . 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, 2018 , 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, 2018 , 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, 2018 , 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, 2018 , the facility fee was 20 basis points. As of December 31, 2018 , we had $11.8 million of outstanding letters of credit, $500.0 million drawn under the revolving credit facility and $1.5 billion outstanding under the term loan facilities, with total undrawn capacity of $1.0 billion under the 2017 credit facility. At December 31, 2018 and December 31, 2017 , the revolving credit facility had a carrying value of $492.2 million and $30.3 million , respectively, net of deferred financing costs. At December 31, 2018 and December 31, 2017 , the term loan facilities had a carrying value of $1.5 billion and $1.5 billion , respectively, net of deferred financing costs. The Company and the Operating Partnership are borrowers jointly and severally obligated 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, 2018 and 2017 , respectively, by scheduled maturity date (amounts in thousands): Issuance December 31, 2018 Unpaid Principal Balance December 31, 2018 Accreted Balance December 31, 2017 Accreted Balance Interest Rate (1) Initial Term (in Years) Maturity Date March 16, 2010 (2) $ 250,000 $ 250,000 $ 250,000 7.75 % 10 March 2020 August 7, 2018 (3) (4) 350,000 350,000 — L+ 0.98 % 3 August 2021 October 5, 2017 (3) 500,000 499,591 499,489 3.25 % 5 October 2022 November 15, 2012 (5) 300,000 304,168 305,163 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 August 5, 2011 (2) (6) — — 249,953 $ 1,500,000 $ 1,503,759 $ 1,404,605 Deferred financing costs, net (8,545 ) (8,666 ) $ 1,500,000 $ 1,495,214 $ 1,395,939 (1) Interest rate as of December 31, 2018 , taking into account interest rate hedges in effect during the period. Floating rate notes are presented with the stated spread over 3-month LIBOR, unless otherwise specified. 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 and the Operating Partnership as co-obligors. (3) Issued by the Operating Partnership with the Company as the guarantor. (4) Beginning on August 8, 2019 and at any time thereafter, the notes are subject to redemption at the Company's option, in whole but not in part, at a redemption price equal to 100% of the principal amount of the notes, plus unpaid accrued interest thereon to the redemption date. (5) In October 2017, the Company and the Operating Partnership 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% . (6) The balance was repaid in August 2018. 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, 2018 and 2017 , 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, 2018 , 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 2019 $ 6,241 $ 27,500 $ — $ — $ — $ — $ 33,741 $ 115,295 2020 11,117 315,523 — — — 250,000 576,640 278,791 2021 11,636 139,869 — — — 350,000 501,505 518,371 2022 9,429 198,588 — — — 800,000 1,008,017 220,810 2023 7,301 115,550 500,000 1,300,000 — — 1,922,851 277,996 Thereafter 9,290 1,136,115 — 200,000 100,000 100,000 1,545,405 2,430,198 $ 55,014 $ 1,933,145 $ 500,000 $ 1,500,000 $ 100,000 $ 1,500,000 $ 5,588,159 $ 3,841,461 Consolidated interest expense, excluding capitalized interest, was comprised of the following (in thousands): Year Ended December 31, 2018 2017 2016 Interest expense before capitalized interest $ 244,788 $ 284,649 $ 348,062 Interest capitalized (34,162 ) (26,020 ) (24,067 ) Interest income (1,957 ) (1,584 ) (2,796 ) Interest expense, net $ 208,669 $ 257,045 $ 321,199

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
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, who serves as a member and as the chairman emeritus 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 , $3.9 million and $3.5 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. We also recorded expenses, inclusive of capitalized expenses, of $18.8 million , $22.6 million and $23.4 million the years ended December 31, 2018 , 2017 and 2016 , 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 $0.6 million , $0.5 million and $0.7 million for the years ended December 31, 2018 , 2017 , and 2016 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, 2018 and 2017 consisted of the following (in thousands): December 31, 2018 2017 Due from joint ventures $ 18,655 $ 15,025 Other 9,378 8,014 Related party receivables $ 28,033 $ 23,039

Noncontrolling Interests on the

Noncontrolling Interests on the Company's Consolidated Financial Statements	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 , the noncontrolling interest unit holders owned 4.70% , or 4,130,579 units, and 4.58% , or 4,452,979 units, of the Operating Partnership, respectively. As of December 31, 2018 , 4,130,579 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 a summary of the activity relating to the noncontrolling interests in the Operating Partnership as of December 31, 2018 and 2017 (in thousands): December 31, 2018 2017 Balance at beginning of period $ 461,954 $ 473,882 Distributions (15,000 ) (14,266 ) Issuance of common units 23,655 25,723 Redemption of common units (60,718 ) (21,574 ) Net income 12,216 3,995 Accumulated other comprehensive income allocation (66 ) (94 ) Fair value adjustment (34,236 ) (5,712 ) Balance at end of period $ 387,805 $ 461,954 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, 2018 , no Subsidiary Series B Preferred Units have been issued. Below is a summary of the activity relating to the preferred units in the Operating Partnership as of December 31, 2018 and 2017 (in thousands): December 31, 2018 2017 Balance at beginning of period $ 301,735 $ 302,010 Issuance of preferred units — — Redemption of preferred units (1,308 ) (275 ) Balance at end of period $ 300,427 $ 301,735

Stockholders' Equity of the Com

Stockholders' Equity of the Company	12 Months Ended
	Dec. 31, 2018
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, 2018 , 83,683,847 shares of common stock and no shares of excess stock were issued and outstanding. Share Repurchase Program In August 2016, our Board of Directors approved a share repurchase plan under which we can buy up to $1.0 billion of shares of our common stock. The Board of Directors has since authorized three separate $500.0 million increases to the size of the share repurchase program in the fourth quarter of 2017, second quarter of 2018, and fourth quarter of 2018, bringing the program total to $2.5 billion . At December 31, 2018 repurchases executed under the plan were as follows: Period Shares repurchased Average price paid per share Cumulative number of shares repurchased as part of the repurchase plan or programs Year ended 2017 8,342,411 $101.64 8,342,411 First quarter 2018 3,653,928 $97.07 11,996,339 Second quarter 2018 3,479,552 $97.22 15,475,891 Third quarter 2018 252,947 $99.75 15,728,838 Fourth quarter 2018 2,358,484 $93.04 18,087,322 At-The-Market Equity Offering Program In March 2015, the Company, along with the Operating Partnership, entered into an "at-the-market" equity offering program, or 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 the ATM program in the years ended December 31, 2018 , 2017 , or 2016 . 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 ("DRSPP") In February 2018, 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 years ended December 31, 2018 , 2017 , and 2016 , respectively (dollars in thousands): Year Ended December 31, 2018 2017 2016 Shares of common stock issued 1,399 2,141 2,687 Dividend reinvestments/stock purchases under the DRSPP $ 136 $ 223 $ 277 Earnings per Share We use the two-class method of computing earnings per share (“EPS”), which is an earnings allocation formula that determines EPS for common stock and any participating securities according to dividends declared (whether paid or unpaid). Under the two-class method, basic EPS is computed by dividing the income available to common stockholders by the weighted-average number of common stock shares outstanding for the period. Diluted EPS reflects the potential dilution that could occur from share equivalent activity. SL Green's earnings per share for the years ended December 31, 2018 , 2017 , and 2016 are computed as follows (in thousands): Year Ended December 31, Numerator 2018 2017 2016 Basic Earnings: Income attributable to SL Green common stockholders $ 232,312 $ 86,424 $ 234,946 Less: distributed earnings allocated to participating securities (552 ) $ (471 ) $ (634 ) Net income attributable to SL Green common stockholders (numerator for basic earnings per share) $ 231,760 $ 85,953 $ 234,312 Add back: undistributed earnings allocated to participating securities 552 471 634 Add back: Effect of dilutive securities (redemption of units to common shares) 12,216 3,995 10,136 Income attributable to SL Green common stockholders (numerator for diluted earnings per share) $ 244,528 $ 90,419 $ 245,082 Year Ended December 31, Denominator 2018 2017 2016 Basic Shares: Weighted average common stock outstanding 86,753 98,571 100,185 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,562 4,556 4,323 Stock-based compensation plans 215 276 373 Diluted weighted average common stock outstanding 91,530 103,403 104,881 SL Green has excluded 1,138,647 , 774,782 and 263,991 common stock equivalents from the diluted shares outstanding for the years ended December 31, 2018 , 2017 , and 2016 respectively, as they were anti-dilutive.

Partners' Capital of the Operat

Partners' Capital of the Operating Partnership	12 Months Ended
	Dec. 31, 2018
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, 2018 , 83,683,847 shares of common stock and no shares of excess stock were issued and outstanding. Share Repurchase Program In August 2016, our Board of Directors approved a share repurchase plan under which we can buy up to $1.0 billion of shares of our common stock. The Board of Directors has since authorized three separate $500.0 million increases to the size of the share repurchase program in the fourth quarter of 2017, second quarter of 2018, and fourth quarter of 2018, bringing the program total to $2.5 billion . At December 31, 2018 repurchases executed under the plan were as follows: Period Shares repurchased Average price paid per share Cumulative number of shares repurchased as part of the repurchase plan or programs Year ended 2017 8,342,411 $101.64 8,342,411 First quarter 2018 3,653,928 $97.07 11,996,339 Second quarter 2018 3,479,552 $97.22 15,475,891 Third quarter 2018 252,947 $99.75 15,728,838 Fourth quarter 2018 2,358,484 $93.04 18,087,322 At-The-Market Equity Offering Program In March 2015, the Company, along with the Operating Partnership, entered into an "at-the-market" equity offering program, or 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 the ATM program in the years ended December 31, 2018 , 2017 , or 2016 . 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 ("DRSPP") In February 2018, 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 years ended December 31, 2018 , 2017 , and 2016 , respectively (dollars in thousands): Year Ended December 31, 2018 2017 2016 Shares of common stock issued 1,399 2,141 2,687 Dividend reinvestments/stock purchases under the DRSPP $ 136 $ 223 $ 277 Earnings per Share We use the two-class method of computing earnings per share (“EPS”), which is an earnings allocation formula that determines EPS for common stock and any participating securities according to dividends declared (whether paid or unpaid). Under the two-class method, basic EPS is computed by dividing the income available to common stockholders by the weighted-average number of common stock shares outstanding for the period. Diluted EPS reflects the potential dilution that could occur from share equivalent activity. SL Green's earnings per share for the years ended December 31, 2018 , 2017 , and 2016 are computed as follows (in thousands): Year Ended December 31, Numerator 2018 2017 2016 Basic Earnings: Income attributable to SL Green common stockholders $ 232,312 $ 86,424 $ 234,946 Less: distributed earnings allocated to participating securities (552 ) $ (471 ) $ (634 ) Net income attributable to SL Green common stockholders (numerator for basic earnings per share) $ 231,760 $ 85,953 $ 234,312 Add back: undistributed earnings allocated to participating securities 552 471 634 Add back: Effect of dilutive securities (redemption of units to common shares) 12,216 3,995 10,136 Income attributable to SL Green common stockholders (numerator for diluted earnings per share) $ 244,528 $ 90,419 $ 245,082 Year Ended December 31, Denominator 2018 2017 2016 Basic Shares: Weighted average common stock outstanding 86,753 98,571 100,185 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,562 4,556 4,323 Stock-based compensation plans 215 276 373 Diluted weighted average common stock outstanding 91,530 103,403 104,881 SL Green has excluded 1,138,647 , 774,782 and 263,991 common stock equivalents from the diluted shares outstanding for the years ended December 31, 2018 , 2017 , and 2016 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 managing general partner of the Operating Partnership and at December 31, 2018 owned 83,683,847 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, 2018 , limited partners other than SL Green owned 4.70% , or 4,130,579 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, 2018 , 2017 , and 2016 respectively are computed as follows (in thousands): Year Ended December 31, Numerator 2018 2017 2016 Basic Earnings: Income attributable to SLGOP common unitholders $ 244,528 $ 90,419 $ 245,082 Less: distributed earnings allocated to participating securities (552 ) $ (471 ) $ (634 ) Net Income attributable to SLGOP common unitholders (numerator for basic earnings per unit) $ 243,976 $ 89,948 $ 244,448 Add back: undistributed earnings allocated to participating securities 552 471 634 Income attributable to SLGOP common unitholders $ 244,528 $ 90,419 $ 245,082 Year Ended December 31, Denominator 2018 2017 2016 Basic units: Weighted average common units outstanding 91,315 103,127 104,508 Effect of Dilutive Securities: Stock-based compensation plans 215 276 373 Diluted weighted average common units outstanding 91,530 103,403 104,881 The Operating Partnership has excluded 1,138,647 , 774,782 , and 263,991 common unit equivalents from the diluted units outstanding for the years ended December 31, 2018 , 2017 , and 2016 respectively, as they were anti-dilutive.

Share-based Compensation

Share-based Compensation	12 Months Ended
	Dec. 31, 2018
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, 2018 , 6.7 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, 2018 , 2017 , and 2016 . 2018 2017 2016 Dividend yield 2.85 % 2.51 % 2.37 % Expected life 3.5 years 4.4 years 3.7 years Risk-free interest rate 2.48 % 1.73 % 1.57 % Expected stock price volatility 22.00 % 28.10 % 26.76 % A summary of the status of the Company's stock options as of December 31, 2018 , 2017 , and 2016 and changes during the years ended December 31, 2018 , 2017 , and 2016 are as follows: 2018 2017 2016 Options Outstanding Weighted Average Exercise Price Options Outstanding Weighted Average Exercise Price Options Weighted Balance at beginning of year $ 1,548,719 $ 101.48 $ 1,737,213 $ 98.44 $ 1,595,007 $ 95.52 Granted 6,000 97.91 174,000 105.66 445,100 105.86 Exercised (316,302 ) 90.22 (292,193 ) 81.07 (192,875 ) 76.90 Lapsed or canceled (101,400 ) 113.22 (70,301 ) 121.68 (110,019 ) 123.86 Balance at end of year $ 1,137,017 $ 135.54 $ 1,548,719 $ 101.48 $ 1,737,213 $ 98.44 Options exercisable at end of year 783,035 $ 101.28 800,902 $ 94.33 748,617 $ 87.72 Weighted average fair value of options granted during the year $ 84,068 $ 3,816,652 $ 8,363,036 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 3.5 years and the remaining weighted average contractual life of the options exercisable was 3.7 years. During the years ended December 31, 2018 , 2017 , and 2016 , we recognized compensation expense for these options of $5.4 million , $7.8 million , and $8.9 million , respectively. As of December 31, 2018 , there was $2.6 million of total unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted average period of 1.0 years. Stock-based Compensation Effective January 1, 1999, the Company implemented a stock-based compensation plan where shares are 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, 2018 , 2017 , and 2016 and charges during the years ended December 31, 2018 , 2017 , and 2016 are as follows: 2018 2017 2016 Balance at beginning of year 3,298,216 3,202,031 3,137,881 Granted 162,900 96,185 98,800 Canceled (9,100 ) — (34,650 ) Balance at end of year 3,452,016 3,298,216 3,202,031 Vested during the year 92,114 95,736 83,822 Compensation expense recorded $ 12,757,704 $ 9,809,749 $ 7,153,966 Weighted average fair value of restricted stock granted during the year $ 13,440,503 $ 9,905,986 $ 10,650,077 The fair value of restricted stock that vested during the years ended December 31, 2018 , 2017 , and 2016 was $9.8 million , $9.4 million and $7.6 million , respectively. As of December 31, 2018 , there was $22.7 million of total unrecognized compensation cost related to restricted stock, which is expected to be recognized over a weighted average period of 2.3 years . For the years ended December 31, 2018 , 2017 , and 2016 , $6.3 million , $7.2 million , and $6.0 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 $22.0 million and $20.5 million during the years ended December 31, 2018 and 2017 , 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, 2018 , there was $2.9 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 1.3 years. During the years ended December 31, 2018 , 2017 , and 2016 , we recorded compensation expense related to bonus, time-based and performance based LTIP Unit awards of $24.4 million , $26.1 million, and $26.5 million , respectively. 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 zero compensation expense during the year ended December 31, 2018 , and compensation expense of $13.6 million and $8.4 million during the years ended December 31, 2017 and 2016 , 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, 2018 , 13,638 phantom stock units were earned and 9,459 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, 2018 related to the Deferred Compensation Plan. As of December 31, 2018 , there were 113,492 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 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, 2018 , 116,368 shares of our common stock had been issued under the ESPP.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2018
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, 2018 , 2017 and 2016 (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, 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 Other comprehensive (loss) income before reclassifications (2,252 ) (103 ) 51 (2,304 ) Amounts reclassified from accumulated other comprehensive income (574 ) (618 ) — (1,192 ) Balance at December 31, 2018 $ 9,716 $ 4,299 $ 1,093 $ 15,108 (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, 2018 and 2017 , 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 $1.3 million and $3.2 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, 2018
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, 2018 and 2017 (in thousands): December 31, 2018 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 28,638 $ — $ 28,638 $ — Interest rate cap and swap agreements (included in other assets) $ 18,676 $ — $ 18,676 $ — Liabilities: Interest rate cap and swap agreements (included in other liabilities) $ 7,663 $ — $ 7,663 $ — 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 $ — We determine 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. In December 2018, the Company determined that it was more likely than not that its suburban properties would be sold or otherwise disposed of significantly before the end of their previously estimated useful life. The Company tested the recoverability of the assets and, as a result of the carrying amount of the assets not being deemed recoverable and exceeding their fair value as measured on a asset by asset basis, recorded a $221.9 million impairment loss. These charges are included in depreciable real estate reserves and impairment in the consolidated statement of operations. The fair value of the assets were determined 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. In May 2018, the Company was the successful bidder at the foreclosure of 2 Herald Square, at which time the Company's $250.5 million outstanding principal balance and $7.7 million accrued interest balance receivables were credited to our equity investment in the property. We recorded the assets acquired and liabilities assumed at fair value. This resulted in the recognition of a fair value adjustment of $8.1 million , which is reflected on the Company's consolidated statement of operations within purchase price and other fair value adjustments. This fair value was determined by utilizing our successful bid at the foreclosure of the asset, the agreement to sell a partial interest in the property, and cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as a sales comparison approach, which utilizes comparable sales, listings and sales contracts, all of which are classified as Level 3 inputs. In January 2018, the partnership agreement for our investment in 919 Third Avenue was modified resulting in the Company no longer having a controlling interest in this investment. As a result the investment was deconsolidated as of January 1, 2018. The Company recorded its non-controlling interest at fair value resulting in a $49.3 million fair value adjustment in the consolidated statement of operations. This fair value was determined using a third party valuation which primarily utilized 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. Marketable securities classified as Level 1 are derived from quoted prices in active markets. The valuation technique used to measure the fair value of 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, 2018 and December 31, 2017 (in thousands): December 31, 2018 December 31, 2017 Carrying Value (1) Fair Value Carrying Value (1) Fair Value Debt and preferred equity investments $ 2,099,393 (2) $ 2,114,041 (2) Fixed rate debt $ 3,543,476 $ 3,230,127 $ 4,305,165 $ 4,421,866 Variable rate debt 2,048,442 2,057,966 1,605,431 1,612,224 $ 5,591,918 $ 5,288,093 $ 5,910,596 $ 6,034,090 (1) Amounts exclude net deferred financing costs. (2) At December 31, 2018 , debt and preferred equity investments had an estimated fair value ranging between $2.1 billion and $2.3 billion . At December 31, 2017 , debt and preferred equity investments had an estimated fair value ranging between $2.1 billion and $2.3 billion . Disclosure about fair value of financial instruments was based on pertinent information available to us as of December 31, 2018 and 2017 . 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, 2018
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 sheet 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, 2018 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 $ 11,148 Interest Rate Swap 100,000 1.161 % July 2016 July 2023 Other Assets 5,447 Interest Rate Cap 137,500 4.000 % September 2017 September 2019 Other Assets — Interest Rate Swap 100,000 1.928 % December 2017 November 2020 Other Assets 1,045 Interest Rate Swap 100,000 1.934 % December 2017 November 2020 Other Assets 1,035 Interest Rate Swap 150,000 2.696 % January 2019 January 2024 Other Liabilities (1,858 ) Interest Rate Swap 150,000 2.721 % January 2019 January 2026 Other Liabilities (2,450 ) Interest Rate Swap 200,000 2.740 % January 2019 January 2026 Other Liabilities (3,354 ) $ 11,013 During the years ended December 31, 2018 , 2017 , and 2016 , we recorded a $0.2 million loss, a $0.5 million loss, and a $0.5 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, 2018 , 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 $7.7 million . As of December 31, 2018 , 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 $7.7 million at December 31, 2018 . 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 $2.5 million of the current balance held in accumulated other comprehensive income will be reclassified into interest expense and $0.6 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, 2018 , 2017 , and 2016 , 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 2018 2017 2016 2018 2017 2016 2018 2017 2016 Interest Rate Swaps/Caps $ (2,284 ) $ (2,282 ) $ 14,616 Interest expense $ 609 $ 1,821 $ 9,521 Interest expense $ (559 ) $ 5 $ (28 ) Share of unconsolidated joint ventures' derivative instruments (1,788 ) (200 ) 2,012 Equity in net income from unconsolidated joint ventures 726 1,035 1,981 Equity in net income from unconsolidated joint ventures (371 ) 55 785 $ (4,072 ) $ (2,482 ) $ 16,628 $ 1,335 $ 2,856 $ 11,502 $ (930 ) $ 60 $ 757

Rental Income

Rental Income	12 Months Ended
	Dec. 31, 2018
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, 2019 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, 2018 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 2019 $ 830,336 $ 348,060 2020 765,610 375,228 2021 625,956 380,886 2022 562,250 348,222 2023 500,499 333,501 Thereafter 3,272,014 2,098,995 $ 6,556,665 $ 3,884,892

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2018
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, 2016, September 28, 2017, and September 28, 2018, the actuary certified that for the plan years beginning July 1, 2016, July 1, 2017, and July 1, 2018, 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, 2018 . For the Pension Plan years ended June 30, 2018 , 2017 , and 2016 , the plan received contributions from employers totaling $272.3 million , $257.8 million , and $249.5 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, 2018 , 2017 , and 2016 , the plan received contributions from employers totaling $1.4 billion , $1.3 billion and $1.2 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, 2018 , 2017 and 2016 are included in the table below (in thousands): Benefit Plan 2018 2017 2016 Pension Plan $ 3,017 $ 3,856 $ 3,979 Health Plan 9,310 11,426 11,530 Other plans 1,106 1,463 1,583 Total plan contributions $ 13,433 $ 16,745 $ 17,092 401(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 2018 , a matching contribution equal to 100% of the first 4% of annual compensation was made. For 2017 and 2016 , a matching contribution equal to 50% of the first 6% of annual compensation was made. For the year ended December 31, 2018 , we made a matching contribution of $1,075,267 . For the years ended December 31, 2017 and 2016 , we made matching contributions of $1,011,830 and $906,875 , respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings As of December 31, 2018 , 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 February 2020 and January 2022. The minimum cash-based compensation, including base salary and guaranteed bonus payments, associated with these employment agreements total $3.3 million for 2019. 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, one of our captive insurance companies, Belmont Insurance Company, or Belmont, provides coverage for NBCR terrorist acts above a specified trigger. Belmont's retention is reinsured by our other captive insurance company, Ticonderoga Insurance Company ("Ticonderoga"). If Belmont or Ticonderoga are required to pay a claim under our insurance policies, we would ultimately record the loss to the extent of required payments. 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 and Ticonderoga provide 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 $4.0 million and $5.5 million as of December 31, 2018 and 2017 , respectively. Ticonderoga had no loss reserves as of December 31, 2018 . 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 ground rent will reset in 2035. 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 30 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 ground rent will reset in 2038. 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 were 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 ground rent will reset in July 2021 to the greater of $5.5 million or 7.75% of the fair value of the land. 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 32 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. 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, 2018 (in thousands): Capital lease Non-cancellable operating leases (1) 2019 $ 2,411 $ 31,066 2020 2,620 31,436 2021 2,794 31,628 2022 2,794 29,472 2023 2,794 27,166 Thereafter 817,100 676,090 Total minimum lease payments $ 830,513 $ 826,858 Amount representing interest (786,897 ) Capital lease obligations $ 43,616 (1) As of December 31, 2018 , the total minimum sublease rentals to be received in the future under non-cancellable subleases is $1.7 billion .

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segment Information	Segment Information The Company has two reportable segments, real estate and debt and preferred equity investments. We evaluate real estate performance and allocate resources based on earnings contributions. 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, insurance, 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 consolidated results of operations for the years ended December 31, 2018 , 2017 , and 2016 , and selected asset information as of December 31, 2018 and 2017 , 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, 2018 $ 1,025,900 $ 201,492 $ 1,227,392 December 31, 2017 1,317,602 193,871 1,511,473 December 31, 2016 1,650,973 213,008 1,863,981 Net Income Years ended: December 31, 2018 $ 129,253 $ 141,603 $ 270,856 December 31, 2017 (69,294 ) 170,363 101,069 December 31, 2016 74,655 204,256 278,911 Total assets As of: December 31, 2018 $ 10,481,594 $ 2,269,764 $ 12,751,358 December 31, 2017 11,598,438 2,384,466 13,982,904 Interest costs for the debt and preferred equity segment include actual costs incurred for borrowings on the 2016 MRA and 2017 MRA. Interest is imputed on the investments that do not collateralize the 2016 MRA or 2017 MRA using our weighted average 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, 2018, 2017, and 2016 marketing, general and administrative expenses totaled $92.6 million , $100.5 million , and $99.8 million respectively. All other expenses, except interest, relate entirely to the real estate assets. There were no transactions between the above two segments.

Quarterly Financial Data of the

Quarterly Financial Data of the Company (unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
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, 2018 and 2017 was as follows (in thousands, except for per share amounts): 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) Gain (loss) on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions 838 (7,507 ) (8,606 ) (8,319 ) Net income attributable to SL Green (57,482 ) 91,947 107,293 105,504 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SL Green common stockholders $ (61,219 ) $ 88,209 $ 103,556 $ 101,766 Net (loss) income attributable to common stockholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common stockholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 $ 398,150 $ 377,381 Total expenses (314,108 ) (333,913 ) (365,749 ) (332,675 ) 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 and impairment (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

Quarterly Financial Data of t_2

Quarterly Financial Data of the Operating Partnership (unaudited)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 was as follows (in thousands, except for per share amounts): 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) Gain (loss) on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions 838 (7,507 ) (8,606 ) (8,319 ) Net income attributable to SL Green (57,482 ) 91,947 107,293 105,504 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SL Green common stockholders $ (61,219 ) $ 88,209 $ 103,556 $ 101,766 Net (loss) income attributable to common stockholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common stockholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 $ 398,150 $ 377,381 Total expenses (314,108 ) (333,913 ) (365,749 ) (332,675 ) 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 and impairment (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
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, 2018 and 2017 was as follows (in thousands, except for per share amounts): 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net (loss) income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) (Loss) gain on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions (2,601 ) (2,710 ) (3,020 ) (3,047 ) Net income attributable to SLOP (60,921 ) 96,744 112,879 110,776 Perpetual preferred units distributions (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SLGOP common unitholders $ (64,658 ) $ 93,006 $ 109,142 $ 107,038 Net (loss) income attributable to common unitholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common unitholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 $ 398,150 $ 377,381 Total expenses (314,108 ) (333,913 ) (365,749 ) (332,675 ) 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 and impairment (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 SLOP 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 share—basic $ 0.29 $ 0.40 $ 0.08 $ 0.11 Net income attributable to common unitholders per common share—diluted $ 0.29 $ 0.40 $ 0.08 $ 0.11

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-09, 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, 2018 Tenant and other receivables—allowance $ 18,637 $ 3,726 $ (6,661 ) $ 15,702 Deferred rent receivable—allowance $ 17,207 $ 491 $ (2,241 ) $ 15,457 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 receivables—allowance $ 17,618 $ 10,630 $ (11,656 ) $ 16,592 Deferred rent receivable—allowance $ 21,730 $ 13,620 $ (10,147 ) $ 25,203 (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, 2018
SEC Schedule, 12-28, Real Estate Companies, Investment in 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 $ — $ 225,667 $ — $ 333,499 $ 333,499 $ 133,978 1927 3/1998 Various 711 Third Avenue(1) — 19,844 42,499 — 73,270 19,844 115,769 135,613 45,066 1955 5/1998 Various 555 W. 57th Street(1) — 18,846 78,704 — 62,242 18,846 140,946 159,792 69,817 1971 1/1999 Various 220 East 42nd Street(1) — 50,373 203,727 635 161,705 51,008 365,432 416,440 108,450 1929 2/2003 Various 461 Fifth Avenue(1) — — 62,695 — 25,581 — 88,276 88,276 29,680 1988 10/2003 Various 750 Third Avenue(1) — 51,093 205,972 — 45,551 51,093 251,523 302,616 101,854 1958 7/2004 Various 625 Madison Avenue(1) — — 246,673 — 44,646 — 291,319 291,319 118,380 1956 10/2004 Various 485 Lexington Avenue(1) 450,000 77,517 326,825 765 125,806 78,282 452,631 530,913 183,003 1956 12/2004 Various 609 Fifth Avenue(1) — 36,677 145,954 — 49,527 36,677 195,481 232,158 43,777 1925 6/2006 Various 810 Seventh Avenue(1) — 114,077 476,386 — 74,433 114,077 550,819 664,896 176,354 1970 1/2007 Various 1185 Avenue of the Americas(1) — — 728,213 — 62,893 — 791,106 791,106 265,896 1969 1/2007 Various 1350 Avenue of the Americas(1) — 91,038 380,744 (97 ) 50,773 90,941 431,517 522,458 136,853 1966 1/2007 Various 100 Summit Lake Drive(2) — 10,526 43,109 (3,337 ) (94 ) 7,189 43,015 50,204 18,936 1988 1/2007 Various 200 Summit Lake Drive(2) — 11,183 47,906 (5,321 ) (9,102 ) 5,862 38,804 44,666 21,203 1990 1/2007 Various 500 Summit Lake Drive(2) — 9,777 39,048 (3,601 ) (7,875 ) 6,176 31,173 37,349 14,523 1986 1/2007 Various 360 Hamilton Avenue(2) — 29,497 118,250 (2,625 ) 8,005 26,872 126,255 153,127 43,901 2000 1/2007 Various 1-6 Landmark Square(3) 100,000 50,947 195,167 (23,095 ) (33,824 ) 27,852 161,343 189,195 79,012 1973-1984 1/2007 Various 7 Landmark Square(3) — 2,088 7,748 (367 ) 669 1,721 8,417 10,138 1,539 2007 1/2007 Various 1010 Washington Boulevard(3) — 7,747 30,423 (1,259 ) 2,928 6,488 33,351 39,839 12,489 1988 1/2007 Various 1055 Washington Boulevard(3) — 13,516 53,228 (5,130 ) (9,986 ) 8,386 43,242 51,628 20,382 1987 6/2007 Various 1 Madison Avenue(1) — 172,641 654,394 905 18,411 173,546 672,805 846,351 193,033 1960 8/2007 Various 100 Church Street(1) 213,208 32,494 79,996 2,500 103,936 34,994 183,932 218,926 53,269 1959 1/2010 Various 125 Park Avenue(1) — 120,900 189,714 — 80,884 120,900 270,598 391,498 77,542 1923 10/2010 Various Williamsburg(4) — 3,677 14,708 2,523 (4,550 ) 6,200 10,158 16,358 2,127 2010 12/2010 Various 110 East 42nd Street(1) — 34,000 46,411 2,196 31,942 36,196 78,353 114,549 17,400 1921 5/2011 Various 400 East 58th Street(1)(5) 39,931 17,549 30,916 — 7,833 17,549 38,749 56,298 6,119 1929 1/2012 Various 752 Madison Avenue(1) — 282,415 7,131 1,871 1,183 284,286 8,314 292,600 1,380 1996/2012 1/2012 Various 762 Madison Avenue(1)(5) 771 6,153 10,461 — 109 6,153 10,570 16,723 1,884 1910 1/2012 Various 19-21 East 65th Street(1) — — 7,389 — 1,100 — 8,489 8,489 1,228 1928-1940 1/2012 Various 304 Park Avenue(1) — 54,189 75,619 300 15,024 54,489 90,643 145,132 19,315 1930 6/2012 Various 635 Sixth Avenue(1) — 24,180 37,158 163 51,103 24,343 88,261 112,604 10,931 1902 9/2012 Various 641 Sixth Avenue(1) — 45,668 67,316 308 9,760 45,976 77,076 123,052 15,891 1902 9/2012 Various 1080 Amsterdam(1)(6) 35,807 — 27,445 — 20,503 — 47,948 47,948 5,441 1932 10/2012 Various 315 West 33rd Street(1) 250,000 195,834 164,429 — 15,133 195,834 179,562 375,396 25,397 2000-2001 11/2013 Various 562 Fifth Avenue(1) — 57,052 10,487 — 1,213 57,052 11,700 68,752 4,458 1909/1920/1921 11/2013 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 719 Seventh Avenue(1)(7) 50,000 41,850 — (670 ) 46,232 41,180 46,232 87,412 3,025 1927 7/2014 Various 115 Spring Street(1) 65,550 11,078 44,799 — 1,850 11,078 46,649 57,727 5,248 1900 7/2014 Various 1640 Flatbush Avenue(4) — 6,226 501 — 503 6,226 1,004 7,230 50 1966 3/2015 Various 110 Greene Street(1)(5) — 45,120 215,470 — 12,923 45,120 228,393 273,513 23,683 1910 7/2015 Various 185 Broadway(1)(8) 111,869 13,400 34,175 32,022 (6,310 ) 45,422 27,865 73,287 419 1921 8/2015 Various 30 East 40th Street(1)(9) — 4,650 20,000 2 6,654 4,652 26,654 31,306 2,017 1927 8/2015 Various 133 Greene Street(1) 15,523 3,446 27,542 — — 3,446 27,542 30,988 119 1900 10/2018 Various 712 Madison Avenue(1) 28,000 7,207 47,397 — — 7,207 47,397 54,604 — 1900/1980 12/2018 Various Other(10) — 1,738 16,225 (2 ) (1 ) 1,736 16,224 17,960 4,068 Total $ 1,660,659 $ 1,776,213 $ 5,370,786 $ (1,314 ) $ 1,368,250 $ 1,774,899 $ 6,739,036 $ 8,513,935 $ 2,099,137 (1) Property located in New York, New York. (2) Property located in Westchester County, New York. (3) Property located in Connecticut. (4) Property located in Brooklyn, New York. (5) We own a 90.0% interest in this property. (6) We own a 92.5% interest in this property. (7) We own a 75.0% interest in this property. (8) Properties at 5-7 Dey Street, 183 Broadway, and 185 Broadway were demolished in preparation of the development site for the 185 Broadway project. (9) We own a 60.0% interest in this property. (10) Other includes tenant improvements of eEmerge, capitalized interest and corporate improvements. The changes in real estate for the years ended December 31, 2018 , 2017 and 2016 are as follows (in thousands): 2018 2017 2016 Balance at beginning of year $ 10,206,122 $ 12,743,332 $ 16,681,602 Property acquisitions 52,939 13,323 29,230 Improvements 267,726 342,014 426,060 Retirements/disposals/deconsolidation (2,012,852 ) (2,892,547 ) (4,393,560 ) Balance at end of year $ 8,513,935 $ 10,206,122 $ 12,743,332 The aggregate cost of land, buildings and improvements, before depreciation, for Federal income tax purposes at December 31, 2018 was $9.9 billion (unaudited). The changes in accumulated depreciation, exclusive of amounts relating to equipment, autos, and furniture and fixtures, for the years ended December 31, 2018 , 2017 and 2016 are as follows (in thousands): 2018 2017 2016 Balance at beginning of year $ 2,300,116 $ 2,264,694 $ 2,060,706 Depreciation for year 245,033 347,015 353,502 Retirements/disposals/deconsolidation (446,012 ) (311,593 ) (149,514 ) Balance at end of year $ 2,099,137 $ 2,300,116 $ 2,264,694

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
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 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.
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, 2018 , the weighted average amortization period for above-market leases, below-market leases, and in-place lease costs is 1.8 years, 4.6 years, and 5.8 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 $242.8 million , $365.3 million , and $783.5 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. On a periodic basis, we assess whether there are any indications that the value of our real estate properties may be 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.
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	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. We determine 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. In December 2018, the Company determined that it was more likely than not that its suburban properties would be sold or otherwise disposed of significantly before the end of their previously estimated useful life. The Company tested the recoverability of the assets and, as a result of the carrying amount of the assets not being deemed recoverable and exceeding their fair value as measured on a asset by asset basis, recorded a $221.9 million impairment loss. These charges are included in depreciable real estate reserves and impairment in the consolidated statement of operations. The fair value of the assets were determined 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. In May 2018, the Company was the successful bidder at the foreclosure of 2 Herald Square, at which time the Company's $250.5 million outstanding principal balance and $7.7 million accrued interest balance receivables were credited to our equity investment in the property. We recorded the assets acquired and liabilities assumed at fair value. This resulted in the recognition of a fair value adjustment of $8.1 million , which is reflected on the Company's consolidated statement of operations within purchase price and other fair value adjustments. This fair value was determined by utilizing our successful bid at the foreclosure of the asset, the agreement to sell a partial interest in the property, and cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as a sales comparison approach, which utilizes comparable sales, listings and sales contracts, all of which are classified as Level 3 inputs. In January 2018, the partnership agreement for our investment in 919 Third Avenue was modified resulting in the Company no longer having a controlling interest in this investment. As a result the investment was deconsolidated as of January 1, 2018. The Company recorded its non-controlling interest at fair value resulting in a $49.3 million fair value adjustment in the consolidated statement of operations. This fair value was determined using a third party valuation which primarily utilized 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. Marketable securities classified as Level 1 are derived from quoted prices in active markets. The valuation technique used to measure the fair value of 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.
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.
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, 2018 , 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. The cost of marketable securities sold and the amount reclassified out of accumulated other comprehensive income into earnings is determined using the specific identification method. Any unrealized losses that are determined to be other-than-temporary are recognized in earnings up to their credit component. The Company adopted ASU 2016-01 effective January 1, 2018 which required entities to measure investments in equity securities at fair value and recognize any changes in fair value in net income. Upon adoption we did not hold investments in equity securities and therefore did not record a cumulative-effect adjustment. We did not hold investments in equity securities as of December 31, 2018 .
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 and includes adjustments related to basis differences that were identified as part of the initial accounting for the investment. 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 a master lease at one joint venture. 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, 2018 . 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 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 financing 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	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 record a gain on sale of real estate assets when we no longer hold a controlling financial interest in the entity holding the real estate, a contract exists with a third party and that third party has control of the assets acquired. Investment 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	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.
Allowance for Loan Loss and Other Investment Reserves	Allowance for Loan Loss and Other Investment Reserves The expense for loan loss and other investment reserves in connection with debt and preferred equity investments is the charge to earnings to adjust the allowance for possible losses to the level that we estimate to be adequate, based on Level 3 data, considering delinquencies, loss experience and collateral quality. The Company evaluates debt and preferred equity investments that are classified as held to maturity for possible impairment or credit deterioration associated with the performance and/or value of the underlying collateral property as well as the financial and operating capability of the borrower/sponsor. Quarterly, the Company assigns each loan a risk rating. Based on a 3-point scale, loans are rated “1” through “3,” from less risk to greater risk, which ratings are defined as follows: 1 - Low Risk Assets - Low probability of loss, 2 - Watch List Assets - Higher potential for loss, 3 - High Risk Assets - Loss more likely than not. When it is probable that we will be unable to collect all amounts contractually due, the investment is considered impaired. 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. Debt and preferred equity investments that are classified as 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. We have elected, and may elect in the future, to treat certain of our 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, 2018 , 2017 and 2016 , we recorded Federal, state and local tax provisions of $2.8 million , $4.3 million , and $2.8 million , respectively. For the year ended December 31, 2018 , the Company paid distributions on its common stock of $3.25 per share which represented $1.46 per share of ordinary income and $1.79 per share of capital gains. 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. 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 and Jobs Act (the ‘‘Tax Act’’) was signed into law and makes substantial changes to the Code. The Tax Act has not had a material impact on our financial statements for the years ended December 31, 2018 or December 31, 2017 .
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, using the two-class method, which is an earnings allocation formula that determines EPS for common stock and any participating securities according to dividends declared (whether paid or unpaid). Under the two-class method, basic EPS is computed by dividing the income available to common stockholders by the weighted-average number of common stock shares outstanding for 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 was no dilutive effect for the exchangeable senior notes as the conversion premium was to 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, using the two-class method, which is an earnings allocation formula that determines EPU for common units and any participating securities according to dividends declared (whether paid or unpaid). Under the two-class method, basic EPU is computed by dividing the income available to common unitholders by the weighted-average number of common units outstanding for 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 was no dilutive effect for the exchangeable senior notes as the conversion premium was to 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 October 2018, the FASB issued Accounting Standard Update (ASU) No. 2018-17, Consolidation (Topic 810), Targeted Improvements to Related Party Guidance for Variable Interest Entities. Under this amendment reporting entities, when determining if the decision-making fees are variable interests, are to consider indirect interests held through related parties under common control on a proportional basis rather than as a direct interest in its entirety. The guidance is effective for the Company for fiscal years beginning after December 15, 2019. Early adoption is permitted. The Company has adopted this guidance and it had no impact on the Company’s consolidated financial statements. In August 2018, The Securities and Exchange Commission adopted a final rule that eliminated or amended disclosure requirements that were redundant or outdated in light of changes in its requirements, generally accepted accounting principles, or changes in the business environment. The commission also referred certain disclosure requirements to the Financial Accounting Standards Board for potential incorporation into generally accepted accounting principles. The rule is effective for filings after November 5, 2018. The Company assessed the impact of this rule and determined that the changes resulted in clarification or expansion of existing requirements. The Company early adopted the rule upon publication to the federal register on October 5, 2018 and it did not have a material impact on the Company’s consolidated financial statements. In August 2018, the FASB issued Accounting Standard Update (ASU) No. 2018-15, Intangibles - Goodwill and Other- Internal-Use Software (Topic 350-40), Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract. The amendments provide guidance on accounting for fees paid when the arrangement includes a software license and align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing costs to develop or obtain internal-use software. The guidance is effective for the Company for fiscal years beginning after December 15, 2019. Early adoption is permitted. The Company has not yet adopted this new guidance and does not expect it to have a material impact on the Company’s consolidated financial statements when the new standard is implemented. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820), Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. This amendment removed, modified and added the disclosure requirements under Topic 820. The changes are effective for the Company for fiscal years beginning after December 15, 2019. Early adoption is permitted for the removed or modified disclosures with adoption of the additional disclosures upon the effective date. The Company has not yet adopted this new guidance and does not expect it to have a material impact on the Company’s consolidated financial statements when the new standard is implemented. In June 2018, the FASB issued ASU No. 2018-07, Compensation - Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting. This amendment provides additional guidance related to share-based payment transactions for acquiring goods or services from nonemployees. The guidance is effective for the Company for fiscal years beginning after December 15, 2018, including the interim periods within that fiscal year. The Company will adopt this guidance January 1, 2019 and does not expect it to have a material impact on the Company’s consolidated financial statements. In February 2018, the FASB issued ASU No. 2018-03, Technical Corrections and Improvements to Financial Instruments- Overall (Subtopic 825-10), Recognition and Measurement of Financial Assets and Financial Liabilities. These amendments provide additional guidance related to equity securities without a readily determinable fair value, forward contracts and options purchased on those equity securities and fair value option liabilities. The Company adopted the guidance on July 1, 2018, and it did not have a material impact on the Company’s consolidated financial statements. In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities, and in July 2018, the FASB issued ASU No. 2018-16, Derivatives and Hedging (Topic 815): Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes. The amendments in the new standards will permit more flexibility in hedging interest rate risk for both variable rate and fixed rate financial instruments. The standards will also enhance the presentation of hedge results in the financial statements. The guidance is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. The Company will adopt this guidance January 1, 2019, and does not expect a material impact on the Company’s consolidated financial statements when the new standards are implemented. In May 2017, the FASB issued 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 Company adopted the guidance on January 1, 2018 and it had no impact on the Company's consolidated financial statements. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. The guidance requires that the statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash. As a result, entities will no longer present transfers between these items on the statement of cash flows. The Company adopted the guidance on January 1, 2018 and has included the changes in restricted cash when reconciling the beginning-of-period and end-of-period total amounts on the statement of cash flows. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments and in November 2018 issued ASU No. 2018-19, Codification Improvements to Topic 326, Financial Instruments - Credit Losses. . 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 15, 2018. The Company’s DPE portfolio and capital lease assets will be subject to this guidance once the Company adopts it. ASU No. 2018-19 excludes operating lease receivables from the scope of this guidance. The Company continues to evaluate the impact of adopting this new accounting standard on the Company’s consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases. In July 2018, the FASB issued ASU No. 2018-10 - Codification Improvements to Topic 842, Leases and ASU No. 2018-11 - Targeted Improvements. In December 2018, the FASB issued ASU No. 2018-20 - Narrow-Scope Improvements for Lessors. This 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 Company will apply this guidance to the 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. While the Company is continuing to assess all potential impacts of the standard, we expect total liabilities and total assets to increase by $0.4 to $0.5 billion as of the date of adoption. The accounting applied by a lessor is largely unchanged from that applied under the previous standard. The Company does expect to adopt the practical expedient offered in ASU No. 2018-11 that allows lessors to not separate non-lease components from the related lease components under certain conditions, which the Company expects most of its leases to qualify for. Additionally, for future leases, the Company will no longer capitalize internal leasing costs as these costs are not considered to be incremental under the new guidance. The Company is assessing all potential impacts of the standard and currently estimates a decrease in net income of approximately $10.0 million related to this change based on its initial assessment. This guidance in this standard is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early adoption is permitted. The Company will adopt this guidance January 1, 2019 and will apply the modified retrospective approach. The Company will elect the package of practical expedients that allows an entity to not reassess (i) whether any expired or existing contracts are or contain leases, (ii) lease classification for any expired or existing leases and (iii) initial direct costs for any expired or existing leases. 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 instrument-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 Company adopted the guidance effective January 1, 2018, and it had no impact on the Company’s consolidated financial statements. 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. The Company adopted this guidance on January 1, 2018. Since the Company’s revenue is related to leasing activities, the adoption of this guidance did 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 did 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. In February 2017, the FASB issued 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 adopted this guidance on January 1, 2018, and applied the modified retrospective approach. The Company elected to adopt the practical expedient under ASC 606, Revenue from Contracts with Customers, which allows an entity to apply the guidance only to contracts with non-customers that are open based on 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 was 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 met the criteria for sale accounting under ASC 610-20. Through the sale, the Company no longer retains a controlling interest, as defined in ASC 810, Consolidation, and the impact of this adjustment is 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. This was recorded in the first quarter of 2018 as an adjustment to beginning retained earnings.

Organization and Basis of Pre_2

Organization and Basis of Presentation (Tables)	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of interests in properties	As of December 31, 2018 , 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 20 12,387,091 10 11,329,183 30 23,716,274 94.5 % Retail 7 (2) 325,648 9 352,174 16 677,822 96.7 % Development/Redevelopment 5 486,101 2 347,000 7 833,101 54.1 % Fee Interest — — 1 — 1 — — % 32 13,198,840 22 12,028,357 54 25,227,197 93.2 % Suburban Office 13 2,295,200 — — 13 2,295,200 91.3 % Retail 1 52,000 — — 1 52,000 100.0 % Development/Redevelopment 1 1,000 — — 1 1,000 — % 15 2,348,200 — — 15 2,348,200 91.4 % Total commercial properties 47 15,547,040 22 12,028,357 69 27,575,397 93.1 % Residential: Manhattan Residential 2 (2) 445,105 10 2,156,751 12 2,601,856 91.5 % Suburban Residential — — — — — — — % Total residential properties 2 445,105 10 2,156,751 12 2,601,856 91.5 % Total portfolio 49 15,992,145 32 14,185,108 81 30,177,253 92.9 % (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) As of December 31, 2018 , we owned a building at 315 West 33rd Street, also known as The Olivia, 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 this 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.

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
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
Schedule of marketable securities	At December 31, 2018 and 2017 , we held the following marketable securities (in thousands): December 31, 2018 2017 Commercial mortgage-backed securities $ 28,638 $ 28,579 Total marketable securities available-for-sale $ 28,638 $ 28,579
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, 2018 and 2017 (in thousands): December 31, 2018 2017 Identified intangible assets (included in other assets): Gross amount $ 266,540 $ 325,880 Accumulated amortization (241,040 ) (277,038 ) Net (1) $ 25,500 $ 48,842 Identified intangible liabilities (included in deferred revenue): Gross amount $ 276,245 $ 540,283 Accumulated amortization (253,767 ) (402,583 ) Net (1) $ 22,478 $ 137,700 (1) As of December 31, 2018 , no net intangible assets and no net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale. 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): 2019 $ (5,227 ) 2020 (3,655 ) 2021 (1,631 ) 2022 (1,328 ) 2023 (749 )
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): 2019 $ 9,825 2020 4,817 2021 3,454 2022 1,892 2023 1,507
Schedules of concentration of risk, by risk factor	For the years ended December 31, 2018, 2017, and 2016, the following properties contributed more than 5.0% of our annualized cash rent, including our share of joint venture annualized cash rent: Property 2018 Property 2017 Property 2016 11 Madison Avenue 7.4% 11 Madison Avenue 7.1% 1515 Broadway 8.8% 1185 Avenue of the Americas 6.7% 1185 Avenue of the Americas 7.1% 1185 Avenue of the Americas 6.9% 420 Lexington Avenue 6.5% 1515 Broadway 7.0% 11 Madison Avenue 6.1% 1515 Broadway 6.0% 420 Lexington Avenue 6.0% 420 Lexington Avenue 5.9% One Madison Avenue 5.8% One Madison Avenue 5.6% One Madison Avenue 5.6%

Property Acquisitions (Tables)

Property Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Schedule of Fair Value of Equity Interest Immediately Before Acquisition Date	During the year ended December 31, 2018 , the properties listed below were acquired from third parties. Property Acquisition Date Property Type Approximate Square Feet Acquisition Price (in millions) 2 Herald Square (1) May 2018 Leasehold Interest 369,000 $ 266.0 1231 Third Avenue (2)(3) July 2018 Fee Interest 39,000 55.4 Upper East Side Residential (3)(4) August 2018 Fee Interest 0.2 acres 30.2 133 Greene Street (2) October 2018 Fee Interest 6,425 31.0 712 Madison Avenue (2) December 2018 Fee Interest 6,600 58.0 (1) In May 2018, the Company was the successful bidder for the leasehold interest in 2 Herald Square, at the foreclosure of the asset. In April and May 2017, the Company had purchased, at par, loans in maturity default that were secured by the leasehold interest in 2 Herald Square. 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 believed that the fair value of the leasehold exceeded the carrying amount of the loans. In May 2018, the Company was the successful bidder at the foreclosure of the asset. We recorded the assets acquired and liabilities assumed at fair value. This resulted in the recognition of a fair value adjustment of $8.1 million , which is reflected in the Company's consolidated statement of operations within purchase price and other fair value adjustments. See Note 16, "Fair Value Measurements." The Company subsequently sold a 49% interest in the property in November 2018. See Note 4, "Properties Held for Sale and Dispositions." and Note 6, "Investments in Unconsolidated Joint Ventures." (2) The Company accepted an assignment of the equity interests in the property in lieu of repayment of the Company's debt investment, and recorded the assets received and liabilities assumed at fair value. (3) This property was subsequently sold in October 2018. See Note 4, "Properties Held for Sale and Dispositions." (4) In August 2018, the Company acquired the fee interest in three additional land parcels at the Upper East Side Residential Assemblage.
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	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 $ —

Properties Held for Sale and _2

Properties Held for Sale and Property Dispositions (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 , 2017 , and 2016 : Property Disposition Date Property Type Unaudited Approximate Usable Square Feet Sales Price (1) (in millions) Gain (Loss) on Sale (2) (in millions) 2 Herald Square (3) November 2018 Office/Retail 369,000 $ 265.0 $ — 400 Summit Lake Drive November 2018 Land 39.5 acres 3.0 (36.2 ) Upper East Side Assemblage (4)(5) October 2018 Development 70,142 143.8 (6.3 ) 1-6 International Drive July 2018 Office 540,000 55.0 (2.6 ) 635 Madison Avenue June 2018 Retail 176,530 153.0 (14.1 ) 115-117 Stevens Avenue May 2018 Office 178,000 12.0 (0.7 ) 600 Lexington Avenue January 2018 Office 303,515 305.0 23.8 1515 Broadway (6) December 2017 Office 1,750,000 1,950.0 — 125 Chubb Way 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 July 2017 Office 325,000 97.0 (44.2 ) 520 White Plains Road 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 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 (9) February 2016 Leased Fee Interest 607,000 453.0 (8.8 ) (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 600 Lexington, 16 Court Street, 102 Greene Street, 400 East 57th Street, 11 Madison Avenue, 388 Greenwich, and 248-252 Bedford Avenue are net of $1.3 million , $2.5 million , $0.9 million , $1.0 million , $0.6 million , $1.6 million , and $1.3 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 2018, the company sold a 49% interest in 2 Herald Square to an Israeli institutional investor. See Note 6, "Investments in Unconsolidated Joint Ventures." (4) Upper East Side Assemblage consists of 260 East 72nd Street, 31,076 square feet of development rights, 252-254 East 72nd Street, 257 East 71st Street, 259 East 71st Street, and 1231 Third Avenue. (5) The Company recorded a $5.8 million charge in 2018 that is included in depreciable real estate reserves and impairment in the consolidated statement of operations. (6) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. At that time, 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." (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. At that time, 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) In February 2016, we closed on the sale of 885 Third Avenue. At that time, 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.

Debt and Preferred Equity Inv_2

Debt and Preferred Equity Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Schedule of debt and preferred equity book balance roll forward	Below is a summary of the activity relating to our debt and preferred equity investments as of December 31, 2018 and 2017 (in thousands): December 31, 2018 December 31, 2017 Balance at beginning of period (1) $ 2,114,041 $ 1,640,412 Debt investment originations/accretion (2) 834,304 1,142,591 Preferred equity investment originations/accretion (2) 151,704 144,456 Redemptions/sales/syndications/amortization (3) (994,906 ) (813,418 ) Net change in loan loss reserves (5,750 ) — Balance at end of period (1) $ 2,099,393 $ 2,114,041 (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 and are included in other assets and other liabilities on the consolidated balance sheets.
Summary of debt investments	As of December 31, 2018 and 2017 , we held the following debt investments with an aggregate weighted average current yield of 8.99% , at December 31, 2018 (in thousands): Loan Type December 31, 2018 Future Funding Obligations December 31, 2018 Senior Financing December 31, 2018 Carrying Value (1) December 31, 2017 Carrying Value (1) Maturity Date (2) Fixed Rate Investments: Mezzanine Loan (3a) $ — $ 1,160,000 $ 213,185 $ 204,005 March 2020 Mezzanine Loan — 15,000 3,500 3,500 September 2021 Mezzanine Loan — 147,000 24,932 24,913 April 2022 Mezzanine Loan — 280,000 36,585 34,600 August 2022 Mezzanine Loan — 85,097 12,706 12,699 November 2023 Mezzanine Loan — 180,000 30,000 — December 2023 Mezzanine Loan (3b) — 115,000 12,941 12,932 June 2024 Mezzanine Loan — 95,000 30,000 30,000 January 2025 Mezzanine Loan — 340,000 11,000 15,000 November 2026 Mezzanine Loan — 1,712,750 55,250 55,250 June 2027 Mortgage/Jr. Mortgage Loan (4) — — — 250,464 Mortgage Loan (5) — — — 26,366 Mortgage Loan (5) — — — 239 Total fixed rate $ — $ 4,129,847 $ 430,099 $ 669,968 Floating Rate Investments: Mezzanine Loan (6) $ — $ 45,025 $ 37,499 $ 34,879 January 2019 Mezzanine Loan (3c)(7) — 85,000 15,333 15,381 March 2019 Mezzanine Loan (3d)(7) — 65,000 14,822 14,869 March 2019 Mezzanine Loan (8) — 38,000 21,990 21,939 March 2019 Mezzanine Loan (7) — 40,000 19,986 19,982 April 2019 Mezzanine Loan — 265,000 24,961 24,830 April 2019 Mortgage/Jr. Mortgage Participation Loan 40,530 233,086 84,012 71,832 August 2019 Mezzanine Loan (7)(8) — 65,000 14,998 14,955 August 2019 Mortgage/Mezzanine Loan (7) — — 19,999 19,940 August 2019 Mortgage/Mezzanine Loan 1,027 — 154,070 143,919 September 2019 Mezzanine Loan — 350,000 34,886 34,737 October 2019 Mortgage/Mezzanine Loan (9) 7,243 — 62,493 43,845 January 2020 Mezzanine Loan (9) 559 575,955 79,164 75,834 January 2020 Mortgage Loan 11,204 — 88,501 — February 2020 Mezzanine Loan 1,277 322,300 53,402 — March 2020 Mortgage/Mezzanine Loan 14,860 — 277,694 — April 2020 Mortgage/Mezzanine Loan (7) — — 37,094 — June 2020 Mezzanine Loan 7,887 38,167 12,627 11,259 July 2020 Mortgage/Mezzanine Loan — — 83,449 — October 2020 Mezzanine Loan 38,575 362,908 88,817 75,428 November 2020 Mortgage/Mezzanine Loan 33,131 — 98,804 88,989 December 2020 Mortgage/Mezzanine Loan — — 35,266 35,152 December 2020 Jr. Mortgage Participation/Mezzanine Loan — 60,000 15,665 15,635 July 2021 Mezzanine Loan (8) — 38,596 7,305 34,947 December 2021 Mortgage/Mezzanine Loan (5) — — — 162,553 Mortgage/Mezzanine Loan (5) — — — 74,755 Mortgage/Mezzanine Loan (10) — — — 23,609 Loan Type December 31, 2018 Future Funding Obligations December 31, 2018 Senior Financing December 31, 2018 Carrying Value (1) December 31, 2017 Carrying Value (1) Maturity Date (2) Mortgage/Mezzanine Loan (5) — — — 16,969 Mezzanine Loan (5) — — — 59,723 Mezzanine Loan (5) — — — 37,851 Mezzanine Loan (5) — — — 14,855 Mezzanine Loan (11) — — — 12,174 Mezzanine Loan (11) — — — 10,934 Mezzanine Loan (5) — — — 37,250 Mezzanine Loan (5) — — — 15,148 Mezzanine Loan (5) — — — 8,550 Mezzanine Loan (11) — — — 26,927 Total floating rate $ 156,293 $ 2,584,037 $ 1,382,837 $ 1,299,650 Total $ 156,293 $ 6,713,884 $ 1,812,936 $ 1,969,618 (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) 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) $1.3 million , (b) $12.0 million , (c) $14.6 million , and (d) $14.1 million . (4) 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 believed that the fair value of the property exceeded the carrying amount of the loans. In May 2018, the Company was the successful bidder at the foreclosure of the asset, at which time the loans were credited to our equity investment in the property. (5) This loan was repaid in 2018. (6) As of January 2019, this loan is in maturity default. No impairment was recorded as the Company believes that the fair value of the property exceeded the carrying amount of the loans. (7) This loan was extended in 2018. (8) This loan was repaid in 2019. (9) This loan was modified in 2019. (10) This loan was sold in 2018. (11) In 2018, the Company accepted an assignment of the equity interests in the property in lieu of repayment of the loan, and recorded the assets received and liabilities assumed at fair value.
Summary of preferred equity investments	As of December 31, 2018 and 2017 , we held the following preferred equity investments with an aggregate weighted average current yield of 9.12% at December 31, 2018 (in thousands): Type December 31, 2018 Future Funding Obligations December 31, 2018 December 31, 2018 (1) December 31, 2017 (1) Mandatory Redemption (2) Preferred Equity (3) $ — $ 272,000 $ 143,183 $ 144,423 April 2021 Preferred Equity — 1,768,000 143,274 — June 2022 $ — $ 2,040,000 $ 286,457 $ 144,423 (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.
Rollforward of total allowance for loan loss reserves	The following table is a rollforward of our total loan loss reserves at December 31, 2018 , 2017 and 2016 (in thousands): December 31, 2018 2017 2016 Balance at beginning of year $ — $ — $ — Expensed 6,839 — — Recoveries — — — Charge-offs and reclassifications (1,089 ) — — Balance at end of period $ 5,750 $ — $ —

Investments in Unconsolidated_2

Investments in Unconsolidated Joint Ventures (Tables)	12 Months Ended
	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	The table below provides general information on each of our joint ventures as of December 31, 2018 : 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 285,000 919 Third Avenue (3) New York State Teacher's Retirement System 51.00% 51.00% 1,454,000 January 2007 1,256,727 11 West 34th Street Private Investor/ Jeff Sutton 30.00% 30.00% 17,150 December 2010 10,800 280 Park Avenue Vornado Realty Trust 50.00% 50.00% 1,219,158 March 2011 400,000 1552-1560 Broadway (4) Jeff Sutton 50.00% 50.00% 57,718 August 2011 136,550 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 (5) Private Investors 32.28% 32.28% 13,069 December 2012 75,000 650 Fifth Avenue (6) 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 55 West 46th Street Prudential Real Estate Investors 25.00% 25.00% 347,000 November 2014 295,000 Stonehenge Portfolio (7) Various Various Various 1,439,016 February 2015 36,668 131-137 Spring Street (8) 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 Private Investors 33.33% 33.33% 26,926 August 2016 — 400 East 57th Street (9) BlackRock, Inc and Stonehenge Partners 51.00% 41.00% 290,482 October 2016 170,000 One Vanderbilt (10) National Pension Service of Korea/Hines Interest LP 71.01% 71.01% — January 2017 3,310,000 Worldwide Plaza RXR Realty / New York REIT / Private Investor 24.35% 24.35% 2,048,725 October 2017 1,725,000 1515 Broadway (11) Allianz Real Estate of America 56.87% 56.87% 1,750,000 November 2017 1,950,000 2 Herald Square Israeli Institutional Investor 51.00% 51.00% 369,000 November 2018 266,000 (1) Ownership interest and economic interest represent the Company's interests in the joint venture as of December 31, 2018 . 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) In January 2018, the partnership agreement for our investment was modified resulting in the Company no longer having a controlling interest in this investment. As a result the investment was deconsolidated as of January 1, 2018. The Company recorded its non-controlling interest at fair value resulting in a $49.3 million fair value adjustment in the consolidated statement of operations. This fair value was allocated to the assets and liabilities, including identified intangibles of the property. (4) 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. (5) 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. (6) 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. (7) In February and March 2018, the Company, together with its joint venture partner, closed on the sale of two properties from the Stonehenge Portfolio. These sales are further described under Sale of Joint Venture Interest of Properties below. (8) In January 2019, we closed on the sale of our interest in this property to our joint venture partner. The transaction generated net cash proceeds to the Company of $15.2 million . (9) In October 2016, the Company sold a 49% interest in this property to an investment account managed by 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. (10) 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, 2018 the total of the two partners' ownership interests based on equity contributed was 23.4% . (11) In November 2017, the Company sold a 30% 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. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and recorded a $0.6 billion gain from the sale of the partial interest and related step-up in basis to fair value of the retained non-controlling interest as an adjustment to beginning retained earnings based on the application of the modified retrospective adoption approach. The Company closed on the sale of an additional 13% interest in the property to Allianz in February 2018. As of December 31, 2018 and 2017 , the carrying value for acquisition, development and construction arrangements were as follows (in thousands): Loan Type December 31, 2018 December 31, 2017 Maturity Date Mezzanine Loan (1) $ 44,357 44,823 February 2022 Mezzanine Loan and Preferred Equity (2) — 100,000 Mezzanine Loan (3) — 26,716 $ 44,357 $ 171,539 (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 mezzanine loan was repaid and the preferred equity interest was redeemed in March 2018. (3) The Company was redeemed on this investment in July 2018.
Schedule of Mortgage and Other Loans Payable on Joint Venture Properties	The first mortgage notes and other loans payable collateralized by the respective joint venture properties and assignment of leases at December 31, 2018 and 2017 , respectively, are as follows (amounts in thousands): Property Economic Interest (1) Maturity Date Interest Rate (2) December 31, 2018 December 31, 2017 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% 210,000 210,000 650 Fifth Avenue (4) 50.00 % October 2022 5.45% 65,000 65,000 21 East 66th Street 32.28 % April 2023 3.60% 12,000 12,000 919 Third Avenue 51.00 % June 2023 5.12% 500,000 — 1515 Broadway 56.87 % March 2025 3.93% 855,876 872,528 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% 99,828 100,000 Worldwide Plaza 24.35 % November 2027 3.98% 1,200,000 1,200,000 Stonehenge Portfolio (5) Various Various 4.20% 321,076 357,282 3 Columbus Circle (6) — 350,000 Total fixed rate debt $ 5,666,108 $ 5,569,138 Floating Rate Debt: 280 Park Avenue 50.00 % September 2019 L+ 1.73% $ 1,200,000 $ 1,200,000 121 Greene Street 50.00 % November 2019 L+ 1.50% 15,000 15,000 10 East 53rd Street 55.00 % February 2020 L+ 2.25% 170,000 170,000 131-137 Spring Street (7) 20.00 % August 2020 L+ 1.55% 141,000 141,000 1552 Broadway 50.00 % October 2020 L+ 2.65% 195,000 195,000 55 West 46th Street (8) 25.00 % November 2020 L+ 2.13% 185,569 171,444 11 West 34th Street 30.00 % January 2021 L+ 1.45% 23,000 23,000 103 East 86th Street (9) 1.00 % January 2021 L+ 1.40% 38,000 55,340 100 Park Avenue 49.90 % February 2021 L+ 1.75% 360,000 360,000 One Vanderbilt (10) 71.01 % September 2021 L+ 2.75% 375,000 355,535 2 Herald Square (11) 51.00 % November 2021 L+ 1.55% 133,565 — 605 West 42nd Street 20.00 % August 2027 L+ 1.44% 550,000 550,000 21 East 66th Street 32.28 % June 2033 1 Year Treasury+ 2.75% 1,571 1,648 175-225 Third Street Brooklyn, New York (12) — 40,000 1745 Broadway (12) — 345,000 Jericho Plaza (13) — 81,099 724 Fifth Avenue (14) — 275,000 Total floating rate debt $ 3,387,705 $ 3,979,066 Total joint venture mortgages and other loans payable $ 9,053,813 $ 9,548,204 Deferred financing costs, net (103,191 ) (136,103 ) Total joint venture mortgages and other loans payable, net $ 8,950,622 $ 9,412,101 (1) Economic interest represents the Company's interests in the joint venture as of December 31, 2018 . Changes in ownership or economic interests, if any, within the current year are disclosed in the notes to the investment in unconsolidated joint ventures table above. (2) Interest rate as of December 31, 2018 , 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) These loans are comprised of a $210.0 million fixed rate mortgage loan and $65.0 million fixed rate mezzanine loan. (5) Amount is comprised of $134.3 million , $54.1 million , and $132.6 million in fixed-rated mortgages that mature in August 2019, June 2024, and April 2028, respectively. (6) In November 2018, we closed on the sale of our interest in the property to our joint venture partner. (7) In January 2019, we closed on the sale of our interest in this property to our joint venture partner. (8) This loan has a committed amount of $195.0 million , of which $9.4 million was unfunded as of December 31, 2018 . (9) In February 2019, along with our joint venture partner, we closed on the sale of the property. (10) This loan is a $1.75 billion construction facility, with reductions in interest cost 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) This loan has a committed amount of $150.0 million . (12) In 2018, along with our joint venture partner, we closed on the sale of the property. (13) In 2018, we closed on the sale of our interest in the property. (14) In 2018, we closed on the sale of substantially all of our interest in the property to our joint venture partner.
Equity Method Investments, Summarized Financial Information Balance Sheet	The combined balance sheets for the unconsolidated joint ventures, at December 31, 2018 and 2017 , are as follows (in thousands): December 31, 2018 December 31, 2017 Assets (1) Commercial real estate property, net $ 14,347,673 $ 12,822,133 Cash and restricted cash 381,301 494,909 Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance 273,141 349,944 Debt and preferred equity investments, net 44,357 202,539 Other assets 2,187,166 1,407,806 Total assets $ 17,233,638 $ 15,277,331 Liabilities and equity (1) Mortgages and other loans payable, net $ 8,950,622 $ 9,412,101 Deferred revenue/gain 1,660,838 985,648 Other liabilities 946,313 411,053 Equity 5,675,865 4,468,529 Total liabilities and equity $ 17,233,638 $ 15,277,331 Company's investments in unconsolidated joint ventures $ 3,019,020 $ 2,362,989 (1) The combined assets, liabilities and equity for the unconsolidated joint ventures reflects the effect of step ups in basis on the retained non-controlling interests in deconsolidated investments as a result of the adoption of ASC 610-20 in January 2018.
Equity Method Investments, Summarized Financial Information Income Statement	(1) The combined assets, liabilities and equity for the unconsolidated joint ventures reflects the effect of step ups in basis on the retained non-controlling interests in deconsolidated investments as a result of the adoption of ASC 610-20 in January 2018. The combined statements of operations for the unconsolidated joint ventures, from acquisition date through the years ended December 31, 2018 , 2017 , and 2016 are as follows (in thousands): Year Ended December 31, 2018 2017 2016 Total revenues $ 1,244,804 $ 904,230 $ 712,689 Operating expenses 219,440 157,610 126,913 Real estate taxes 226,961 142,774 111,673 Ground rent 18,697 16,794 14,924 Interest expense, net of interest income 363,055 250,063 197,741 Amortization of deferred financing costs 21,634 23,026 24,829 Transaction related costs — 146 5,566 Depreciation and amortization 421,458 279,419 199,011 Total expenses $ 1,271,245 $ 869,832 $ 680,657 Loss on early extinguishment of debt — (7,899 ) (1,606 ) Net (loss) income before gain on sale (1) $ (26,441 ) $ 26,499 $ 30,426 Company's equity in net income from unconsolidated joint ventures (1) $ 7,311 $ 21,892 $ 11,874 (1) The combined statements of operations and the Company's equity in net income for the unconsolidated joint ventures reflects the effect of step ups in basis on the retained non-controlling interests in deconsolidated investments as a result of the adoption of ASC 610-20 in January 2018.
Discontinued Operations, Disposed of by Sale
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	The following table summarizes the investments in unconsolidated joint ventures sold during the years ended December 31, 2018 , 2017 , and 2016 : Property Ownership Interest Sold Disposition Date Type of Sale Gross Asset Valuation (in thousands) (1) Gain (Loss) on Sale (in thousands) (2) 3 Columbus Circle 48.90% November 2018 Ownership Interest $ 851,000 $ 160,368 Mezzanine Loan (3) 33.33% August 2018 Repayment 15,000 N/A 724 Fifth Avenue 49.90% July 2018 Ownership Interest 365,000 64,587 Jericho Plaza (4) 11.67% June 2018 Ownership Interest 117,400 147 1745 Broadway 56.87% May 2018 Property 633,000 52,038 175-225 Third Street Brooklyn, New York 95.00% April 2018 Property 115,000 19,483 Stonehenge Village (5) 0.50% March 2018 Property 287,000 (5,701 ) 1515 Broadway (6) 13.00% February 2018 Ownership Interest 1,950,000 — 1274 Fifth Avenue (5) 9.83% February 2018 Property 44,100 (362 ) 102 Greene Street 10.00% September 2017 Ownership Interest 43,500 283 76 11th Avenue (7) 33.33% May 2017 Repayment 138,240 N/A Stonehenge Portfolio (partial) (6) Various March 2017 Ownership Interest 300,000 871 EOP Denver 0.48% September 2016 Ownership Interest 180,700 300 33 Beekman (8) 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 Jericho Plaza (4) 66.11% February 2016 Ownership Interest 95,200 3,300 (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 $11.7 million , $0 , and $1.1 million of employee compensation accrued in connection with the realization of these investment gains in the years ended December 31, 2018 , 2017 , and 2016 , respectively. Additionally, gain (loss) amounts do not include adjustments for expenses recorded in subsequent periods. (3) Our investment in a joint venture that owned a mezzanine loan secured by a commercial property in midtown Manhattan was repaid after the joint venture received repayment of the underlying loan. (4) We sold our 11.67 % interest in June 2018. In the first quarter of 2016, our ownership percentage was reduced from 77.78 % to 11.67 %, upon completion of a restructuring of the joint venture. (5) Properties were part of the Stonehenge Portfolio. (6) Our investment in 1515 Broadway was marked to fair value on January 1, 2018 upon adoption of ASC 610-20. (7) 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. (8) In connection with the sale of the property, we also recognized a promote of $10.8 million .

Deferred Costs (Tables)

Deferred Costs (Tables)	12 Months Ended
	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Deferred Costs	Deferred costs at December 31, 2018 and 2017 consisted of the following (in thousands): December 31, 2018 2017 Deferred leasing costs $ 453,833 $ 443,341 Less: accumulated amortization (244,723 ) (217,140 ) Deferred costs, net $ 209,110 $ 226,201

Mortgages and Other Loans Pay_2

Mortgages and Other Loans Payable (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) December 31, 2018 December 31, 2017 Fixed Rate Debt: 762 Madison Avenue February 2022 5.00% 771 771 100 Church Street July 2022 4.68% 213,208 217,273 420 Lexington Avenue October 2024 3.99% 300,000 300,000 400 East 58th Street (2) November 2026 3.00% 39,931 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 (3) February 2027 3.58% 35,807 36,363 315 West 33rd Street February 2027 4.17% 250,000 250,000 919 Third Avenue (4) — 500,000 Unsecured Loan (5) — 16,000 Series J Preferred Units (6) — 4,000 One Madison Avenue (7) — 486,153 Total fixed rate debt $ 1,389,717 $ 2,400,560 Floating Rate Debt: FHLB Facility May 2019 L+ 0.27% $ 13,000 $ — 2017 Master Repurchase Agreement June 2019 L+ 2.34% 300,000 90,809 FHLB Facility December 2019 L+ 0.18% 14,500 — 133 Greene Street August 2020 L+ 2.00% 15,523 — 185 Broadway (8) November 2021 L+ 2.85% 111,869 58,000 712 Madison December 2021 L+ 2.50% 28,000 — 115 Spring Street September 2023 L+ 3.40% 65,550 — 719 Seventh Avenue September 2023 L+ 1.20% 50,000 41,622 220 East 42nd Street (9) — 275,000 Total floating rate debt $ 598,442 $ 465,431 Total fixed rate and floating rate debt $ 1,988,159 $ 2,865,991 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 1,988,159 $ 2,865,991 Deferred financing costs, net of amortization (26,919 ) (28,709 ) Total mortgages and other loans payable, net $ 1,961,240 $ 2,837,282 (1) Interest rate as of December 31, 2018 , 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) 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 . (3) 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 . (4) Our investment in the property was deconsolidated as of January 1, 2018. See Note 6, "Investments in Unconsolidated Joint Ventures". (5) In May 2018, the loan was repaid in connection with the sale of the property. (6) In June 2018, the Series J Preferred Units were redeemed in connection with the sale of the property. (7) In 2018, the Company recognized a $14.9 million loss on extinguishment of debt related to the early repayment of this loan. (8) This loan is a $225.0 million construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial three -year term with two one -year extension options. cured Notes The following table sets forth our senior unsecured notes and other related disclosures as of December 31, 2018 and 2017 , respectively, by scheduled maturity date (amounts in thousands): Issuance December 31, 2018 Unpaid Principal Balance December 31, 2018 Accreted Balance December 31, 2017 Accreted Balance Interest Rate (1) Initial Term (in Years) Maturity Date March 16, 2010 (2) $ 250,000 $ 250,000 $ 250,000 7.75 % 10 March 2020 August 7, 2018 (3) (4) 350,000 350,000 — L+ 0.98 % 3 August 2021 October 5, 2017 (3) 500,000 499,591 499,489 3.25 % 5 October 2022 November 15, 2012 (5) 300,000 304,168 305,163 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 August 5, 2011 (2) (6) — — 249,953 $ 1,500,000 $ 1,503,759 $ 1,404,605 Deferred financing costs, net (8,545 ) (8,666 ) $ 1,500,000 $ 1,495,214 $ 1,395,939 (1) Interest rate as of December 31, 2018 , taking into account interest rate hedges in effect during the period. Floating rate notes are presented with the stated spread over 3-month LIBOR, unless otherwise specified. 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 and the Operating Partnership as co-obligors. (3) Issued by the Operating Partnership with the Company as the guarantor. (4) Beginning on August 8, 2019 and at any time thereafter, the notes are subject to redemption at the Company's option, in whole but not in part, at a redemption price equal to 100% of the principal amount of the notes, plus unpaid accrued interest thereon to the redemption date. (5) In October 2017, the Company and the Operating Partnership 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% . (6)

Corporate Indebtedness (Tables)

Corporate Indebtedness (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) December 31, 2018 December 31, 2017 Fixed Rate Debt: 762 Madison Avenue February 2022 5.00% 771 771 100 Church Street July 2022 4.68% 213,208 217,273 420 Lexington Avenue October 2024 3.99% 300,000 300,000 400 East 58th Street (2) November 2026 3.00% 39,931 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 (3) February 2027 3.58% 35,807 36,363 315 West 33rd Street February 2027 4.17% 250,000 250,000 919 Third Avenue (4) — 500,000 Unsecured Loan (5) — 16,000 Series J Preferred Units (6) — 4,000 One Madison Avenue (7) — 486,153 Total fixed rate debt $ 1,389,717 $ 2,400,560 Floating Rate Debt: FHLB Facility May 2019 L+ 0.27% $ 13,000 $ — 2017 Master Repurchase Agreement June 2019 L+ 2.34% 300,000 90,809 FHLB Facility December 2019 L+ 0.18% 14,500 — 133 Greene Street August 2020 L+ 2.00% 15,523 — 185 Broadway (8) November 2021 L+ 2.85% 111,869 58,000 712 Madison December 2021 L+ 2.50% 28,000 — 115 Spring Street September 2023 L+ 3.40% 65,550 — 719 Seventh Avenue September 2023 L+ 1.20% 50,000 41,622 220 East 42nd Street (9) — 275,000 Total floating rate debt $ 598,442 $ 465,431 Total fixed rate and floating rate debt $ 1,988,159 $ 2,865,991 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 1,988,159 $ 2,865,991 Deferred financing costs, net of amortization (26,919 ) (28,709 ) Total mortgages and other loans payable, net $ 1,961,240 $ 2,837,282 (1) Interest rate as of December 31, 2018 , 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) 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 . (3) 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 . (4) Our investment in the property was deconsolidated as of January 1, 2018. See Note 6, "Investments in Unconsolidated Joint Ventures". (5) In May 2018, the loan was repaid in connection with the sale of the property. (6) In June 2018, the Series J Preferred Units were redeemed in connection with the sale of the property. (7) In 2018, the Company recognized a $14.9 million loss on extinguishment of debt related to the early repayment of this loan. (8) This loan is a $225.0 million construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial three -year term with two one -year extension options. cured Notes The following table sets forth our senior unsecured notes and other related disclosures as of December 31, 2018 and 2017 , respectively, by scheduled maturity date (amounts in thousands): Issuance December 31, 2018 Unpaid Principal Balance December 31, 2018 Accreted Balance December 31, 2017 Accreted Balance Interest Rate (1) Initial Term (in Years) Maturity Date March 16, 2010 (2) $ 250,000 $ 250,000 $ 250,000 7.75 % 10 March 2020 August 7, 2018 (3) (4) 350,000 350,000 — L+ 0.98 % 3 August 2021 October 5, 2017 (3) 500,000 499,591 499,489 3.25 % 5 October 2022 November 15, 2012 (5) 300,000 304,168 305,163 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 August 5, 2011 (2) (6) — — 249,953 $ 1,500,000 $ 1,503,759 $ 1,404,605 Deferred financing costs, net (8,545 ) (8,666 ) $ 1,500,000 $ 1,495,214 $ 1,395,939 (1) Interest rate as of December 31, 2018 , taking into account interest rate hedges in effect during the period. Floating rate notes are presented with the stated spread over 3-month LIBOR, unless otherwise specified. 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 and the Operating Partnership as co-obligors. (3) Issued by the Operating Partnership with the Company as the guarantor. (4) Beginning on August 8, 2019 and at any time thereafter, the notes are subject to redemption at the Company's option, in whole but not in part, at a redemption price equal to 100% of the principal amount of the notes, plus unpaid accrued interest thereon to the redemption date. (5) In October 2017, the Company and the Operating Partnership 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% . (6)
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, 2018 , 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 2019 $ 6,241 $ 27,500 $ — $ — $ — $ — $ 33,741 $ 115,295 2020 11,117 315,523 — — — 250,000 576,640 278,791 2021 11,636 139,869 — — — 350,000 501,505 518,371 2022 9,429 198,588 — — — 800,000 1,008,017 220,810 2023 7,301 115,550 500,000 1,300,000 — — 1,922,851 277,996 Thereafter 9,290 1,136,115 — 200,000 100,000 100,000 1,545,405 2,430,198 $ 55,014 $ 1,933,145 $ 500,000 $ 1,500,000 $ 100,000 $ 1,500,000 $ 5,588,159 $ 3,841,461
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, 2018 2017 2016 Interest expense before capitalized interest $ 244,788 $ 284,649 $ 348,062 Interest capitalized (34,162 ) (26,020 ) (24,067 ) Interest income (1,957 ) (1,584 ) (2,796 ) Interest expense, net $ 208,669 $ 257,045 $ 321,199

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Schedule of amounts due from/to related parties	Amounts due from joint ventures and related parties at December 31, 2018 and 2017 consisted of the following (in thousands): December 31, 2018 2017 Due from joint ventures $ 18,655 $ 15,025 Other 9,378 8,014 Related party receivables $ 28,033 $ 23,039

Noncontrolling Interests on t_2

Noncontrolling Interests on the Company's Consolidated Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2018
Noncontrolling Interest [Abstract]
Schedule of Noncontrolling Interest	Below is a summary of the activity relating to the noncontrolling interests in the Operating Partnership as of December 31, 2018 and 2017 (in thousands): December 31, 2018 2017 Balance at beginning of period $ 461,954 $ 473,882 Distributions (15,000 ) (14,266 ) Issuance of common units 23,655 25,723 Redemption of common units (60,718 ) (21,574 ) Net income 12,216 3,995 Accumulated other comprehensive income allocation (66 ) (94 ) Fair value adjustment (34,236 ) (5,712 ) Balance at end of period $ 387,805 $ 461,954
Schedule of Preferred Unit Activity	Below is a summary of the activity relating to the preferred units in the Operating Partnership as of December 31, 2018 and 2017 (in thousands): December 31, 2018 2017 Balance at beginning of period $ 301,735 $ 302,010 Issuance of preferred units — — Redemption of preferred units (1,308 ) (275 ) Balance at end of period $ 300,427 $ 301,735

Stockholders' Equity of the C_2

Stockholders' Equity of the Company (Tables)	12 Months Ended
	Dec. 31, 2018
Stockholders' Equity Note [Abstract]
Class of Treasury Stock	At December 31, 2018 repurchases executed under the plan were as follows: Period Shares repurchased Average price paid per share Cumulative number of shares repurchased as part of the repurchase plan or programs Year ended 2017 8,342,411 $101.64 8,342,411 First quarter 2018 3,653,928 $97.07 11,996,339 Second quarter 2018 3,479,552 $97.22 15,475,891 Third quarter 2018 252,947 $99.75 15,728,838 Fourth quarter 2018 2,358,484 $93.04 18,087,322
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 years ended December 31, 2018 , 2017 , and 2016 , respectively (dollars in thousands): Year Ended December 31, 2018 2017 2016 Shares of common stock issued 1,399 2,141 2,687 Dividend reinvestments/stock purchases under the DRSPP $ 136 $ 223 $ 277
Schedule of Earnings Per Share	SL Green's earnings per share for the years ended December 31, 2018 , 2017 , and 2016 are computed as follows (in thousands): Year Ended December 31, Numerator 2018 2017 2016 Basic Earnings: Income attributable to SL Green common stockholders $ 232,312 $ 86,424 $ 234,946 Less: distributed earnings allocated to participating securities (552 ) $ (471 ) $ (634 ) Net income attributable to SL Green common stockholders (numerator for basic earnings per share) $ 231,760 $ 85,953 $ 234,312 Add back: undistributed earnings allocated to participating securities 552 471 634 Add back: Effect of dilutive securities (redemption of units to common shares) 12,216 3,995 10,136 Income attributable to SL Green common stockholders (numerator for diluted earnings per share) $ 244,528 $ 90,419 $ 245,082 Year Ended December 31, Denominator 2018 2017 2016 Basic Shares: Weighted average common stock outstanding 86,753 98,571 100,185 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,562 4,556 4,323 Stock-based compensation plans 215 276 373 Diluted weighted average common stock outstanding 91,530 103,403 104,881 The Operating Partnership's earnings per unit for the years ended December 31, 2018 , 2017 , and 2016 respectively are computed as follows (in thousands): Year Ended December 31, Numerator 2018 2017 2016 Basic Earnings: Income attributable to SLGOP common unitholders $ 244,528 $ 90,419 $ 245,082 Less: distributed earnings allocated to participating securities (552 ) $ (471 ) $ (634 ) Net Income attributable to SLGOP common unitholders (numerator for basic earnings per unit) $ 243,976 $ 89,948 $ 244,448 Add back: undistributed earnings allocated to participating securities 552 471 634 Income attributable to SLGOP common unitholders $ 244,528 $ 90,419 $ 245,082 Year Ended December 31, Denominator 2018 2017 2016 Basic units: Weighted average common units outstanding 91,315 103,127 104,508 Effect of Dilutive Securities: Stock-based compensation plans 215 276 373 Diluted weighted average common units outstanding 91,530 103,403 104,881

Partners' Capital of the Oper_2

Partners' Capital of the Operating Partnership (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Earnings Per Share	SL Green's earnings per share for the years ended December 31, 2018 , 2017 , and 2016 are computed as follows (in thousands): Year Ended December 31, Numerator 2018 2017 2016 Basic Earnings: Income attributable to SL Green common stockholders $ 232,312 $ 86,424 $ 234,946 Less: distributed earnings allocated to participating securities (552 ) $ (471 ) $ (634 ) Net income attributable to SL Green common stockholders (numerator for basic earnings per share) $ 231,760 $ 85,953 $ 234,312 Add back: undistributed earnings allocated to participating securities 552 471 634 Add back: Effect of dilutive securities (redemption of units to common shares) 12,216 3,995 10,136 Income attributable to SL Green common stockholders (numerator for diluted earnings per share) $ 244,528 $ 90,419 $ 245,082 Year Ended December 31, Denominator 2018 2017 2016 Basic Shares: Weighted average common stock outstanding 86,753 98,571 100,185 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,562 4,556 4,323 Stock-based compensation plans 215 276 373 Diluted weighted average common stock outstanding 91,530 103,403 104,881 The Operating Partnership's earnings per unit for the years ended December 31, 2018 , 2017 , and 2016 respectively are computed as follows (in thousands): Year Ended December 31, Numerator 2018 2017 2016 Basic Earnings: Income attributable to SLGOP common unitholders $ 244,528 $ 90,419 $ 245,082 Less: distributed earnings allocated to participating securities (552 ) $ (471 ) $ (634 ) Net Income attributable to SLGOP common unitholders (numerator for basic earnings per unit) $ 243,976 $ 89,948 $ 244,448 Add back: undistributed earnings allocated to participating securities 552 471 634 Income attributable to SLGOP common unitholders $ 244,528 $ 90,419 $ 245,082 Year Ended December 31, Denominator 2018 2017 2016 Basic units: Weighted average common units outstanding 91,315 103,127 104,508 Effect of Dilutive Securities: Stock-based compensation plans 215 276 373 Diluted weighted average common units outstanding 91,530 103,403 104,881

Share-based Compensation (Table

Share-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 , 2017 , and 2016 . 2018 2017 2016 Dividend yield 2.85 % 2.51 % 2.37 % Expected life 3.5 years 4.4 years 3.7 years Risk-free interest rate 2.48 % 1.73 % 1.57 % Expected stock price volatility 22.00 % 28.10 % 26.76 %
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, 2018 , 2017 , and 2016 and changes during the years ended December 31, 2018 , 2017 , and 2016 are as follows: 2018 2017 2016 Options Outstanding Weighted Average Exercise Price Options Outstanding Weighted Average Exercise Price Options Weighted Balance at beginning of year $ 1,548,719 $ 101.48 $ 1,737,213 $ 98.44 $ 1,595,007 $ 95.52 Granted 6,000 97.91 174,000 105.66 445,100 105.86 Exercised (316,302 ) 90.22 (292,193 ) 81.07 (192,875 ) 76.90 Lapsed or canceled (101,400 ) 113.22 (70,301 ) 121.68 (110,019 ) 123.86 Balance at end of year $ 1,137,017 $ 135.54 $ 1,548,719 $ 101.48 $ 1,737,213 $ 98.44 Options exercisable at end of year 783,035 $ 101.28 800,902 $ 94.33 748,617 $ 87.72 Weighted average fair value of options granted during the year $ 84,068 $ 3,816,652 $ 8,363,036
Schedule of other share-based compensation, activity	A summary of the Company's restricted stock as of December 31, 2018 , 2017 , and 2016 and charges during the years ended December 31, 2018 , 2017 , and 2016 are as follows: 2018 2017 2016 Balance at beginning of year 3,298,216 3,202,031 3,137,881 Granted 162,900 96,185 98,800 Canceled (9,100 ) — (34,650 ) Balance at end of year 3,452,016 3,298,216 3,202,031 Vested during the year 92,114 95,736 83,822 Compensation expense recorded $ 12,757,704 $ 9,809,749 $ 7,153,966 Weighted average fair value of restricted stock granted during the year $ 13,440,503 $ 9,905,986 $ 10,650,077

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income	The following tables set forth the changes in accumulated other comprehensive income (loss) by component as of December 31, 2018 , 2017 and 2016 (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, 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 Other comprehensive (loss) income before reclassifications (2,252 ) (103 ) 51 (2,304 ) Amounts reclassified from accumulated other comprehensive income (574 ) (618 ) — (1,192 ) Balance at December 31, 2018 $ 9,716 $ 4,299 $ 1,093 $ 15,108 (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, 2018 and 2017 , 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 $1.3 million and $3.2 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, 2018
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, 2018 and 2017 (in thousands): December 31, 2018 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 28,638 $ — $ 28,638 $ — Interest rate cap and swap agreements (included in other assets) $ 18,676 $ — $ 18,676 $ — Liabilities: Interest rate cap and swap agreements (included in other liabilities) $ 7,663 $ — $ 7,663 $ — 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 $ —
Fair Value, by Balance Sheet Grouping	The following table provides the carrying value and fair value of these financial instruments as of December 31, 2018 and December 31, 2017 (in thousands): December 31, 2018 December 31, 2017 Carrying Value (1) Fair Value Carrying Value (1) Fair Value Debt and preferred equity investments $ 2,099,393 (2) $ 2,114,041 (2) Fixed rate debt $ 3,543,476 $ 3,230,127 $ 4,305,165 $ 4,421,866 Variable rate debt 2,048,442 2,057,966 1,605,431 1,612,224 $ 5,591,918 $ 5,288,093 $ 5,910,596 $ 6,034,090 (1) Amounts exclude net deferred financing costs. (2) At December 31, 2018 , debt and preferred equity investments had an estimated fair value ranging between $2.1 billion and $2.3 billion . At December 31, 2017 , debt and preferred equity investments had an estimated fair value ranging between $2.1 billion and $2.3 billion .

Financial Instruments_ Deriva_2

Financial Instruments: Derivatives and Hedging (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 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 $ 11,148 Interest Rate Swap 100,000 1.161 % July 2016 July 2023 Other Assets 5,447 Interest Rate Cap 137,500 4.000 % September 2017 September 2019 Other Assets — Interest Rate Swap 100,000 1.928 % December 2017 November 2020 Other Assets 1,045 Interest Rate Swap 100,000 1.934 % December 2017 November 2020 Other Assets 1,035 Interest Rate Swap 150,000 2.696 % January 2019 January 2024 Other Liabilities (1,858 ) Interest Rate Swap 150,000 2.721 % January 2019 January 2026 Other Liabilities (2,450 ) Interest Rate Swap 200,000 2.740 % January 2019 January 2026 Other Liabilities (3,354 ) $ 11,013
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, 2018 , 2017 , and 2016 , 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 2018 2017 2016 2018 2017 2016 2018 2017 2016 Interest Rate Swaps/Caps $ (2,284 ) $ (2,282 ) $ 14,616 Interest expense $ 609 $ 1,821 $ 9,521 Interest expense $ (559 ) $ 5 $ (28 ) Share of unconsolidated joint ventures' derivative instruments (1,788 ) (200 ) 2,012 Equity in net income from unconsolidated joint ventures 726 1,035 1,981 Equity in net income from unconsolidated joint ventures (371 ) 55 785 $ (4,072 ) $ (2,482 ) $ 16,628 $ 1,335 $ 2,856 $ 11,502 $ (930 ) $ 60 $ 757

Rental Income (Tables)

Rental Income (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 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 2019 $ 830,336 $ 348,060 2020 765,610 375,228 2021 625,956 380,886 2022 562,250 348,222 2023 500,499 333,501 Thereafter 3,272,014 2,098,995 $ 6,556,665 $ 3,884,892

Benefit Plans (Tables)

Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 , 2017 and 2016 are included in the table below (in thousands): Benefit Plan 2018 2017 2016 Pension Plan $ 3,017 $ 3,856 $ 3,979 Health Plan 9,310 11,426 11,530 Other plans 1,106 1,463 1,583 Total plan contributions $ 13,433 $ 16,745 $ 17,092

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 (in thousands): Capital lease Non-cancellable operating leases (1) 2019 $ 2,411 $ 31,066 2020 2,620 31,436 2021 2,794 31,628 2022 2,794 29,472 2023 2,794 27,166 Thereafter 817,100 676,090 Total minimum lease payments $ 830,513 $ 826,858 Amount representing interest (786,897 ) Capital lease obligations $ 43,616 (1) As of December 31, 2018 , the total minimum sublease rentals to be received in the future under non-cancellable subleases is $1.7 billion .
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, 2018 (in thousands): Capital lease Non-cancellable operating leases (1) 2019 $ 2,411 $ 31,066 2020 2,620 31,436 2021 2,794 31,628 2022 2,794 29,472 2023 2,794 27,166 Thereafter 817,100 676,090 Total minimum lease payments $ 830,513 $ 826,858 Amount representing interest (786,897 ) Capital lease obligations $ 43,616

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Schedule of selected results of operations and selected asset information	Selected consolidated results of operations for the years ended December 31, 2018 , 2017 , and 2016 , and selected asset information as of December 31, 2018 and 2017 , 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, 2018 $ 1,025,900 $ 201,492 $ 1,227,392 December 31, 2017 1,317,602 193,871 1,511,473 December 31, 2016 1,650,973 213,008 1,863,981 Net Income Years ended: December 31, 2018 $ 129,253 $ 141,603 $ 270,856 December 31, 2017 (69,294 ) 170,363 101,069 December 31, 2016 74,655 204,256 278,911 Total assets As of: December 31, 2018 $ 10,481,594 $ 2,269,764 $ 12,751,358 December 31, 2017 11,598,438 2,384,466 13,982,904

Quarterly Financial Data of t_3

Quarterly Financial Data of the Company (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Summarized quarterly financial data for the years ended December 31, 2018 and 2017 was as follows (in thousands, except for per share amounts): 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) Gain (loss) on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions 838 (7,507 ) (8,606 ) (8,319 ) Net income attributable to SL Green (57,482 ) 91,947 107,293 105,504 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SL Green common stockholders $ (61,219 ) $ 88,209 $ 103,556 $ 101,766 Net (loss) income attributable to common stockholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common stockholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 $ 398,150 $ 377,381 Total expenses (314,108 ) (333,913 ) (365,749 ) (332,675 ) 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 and impairment (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

Quarterly Financial Data of t_4

Quarterly Financial Data of the Operating Partnership (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Condensed Income Statements, Captions [Line Items]
Schedule of Quarterly Financial Information	Summarized quarterly financial data for the years ended December 31, 2018 and 2017 was as follows (in thousands, except for per share amounts): 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) Gain (loss) on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions 838 (7,507 ) (8,606 ) (8,319 ) Net income attributable to SL Green (57,482 ) 91,947 107,293 105,504 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SL Green common stockholders $ (61,219 ) $ 88,209 $ 103,556 $ 101,766 Net (loss) income attributable to common stockholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common stockholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 $ 398,150 $ 377,381 Total expenses (314,108 ) (333,913 ) (365,749 ) (332,675 ) 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 and impairment (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
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, 2018 and 2017 was as follows (in thousands, except for per share amounts): 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net (loss) income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) (Loss) gain on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions (2,601 ) (2,710 ) (3,020 ) (3,047 ) Net income attributable to SLOP (60,921 ) 96,744 112,879 110,776 Perpetual preferred units distributions (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SLGOP common unitholders $ (64,658 ) $ 93,006 $ 109,142 $ 107,038 Net (loss) income attributable to common unitholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common unitholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 2017 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 361,342 $ 374,600 $ 398,150 $ 377,381 Total expenses (314,108 ) (333,913 ) (365,749 ) (332,675 ) 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 and impairment (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 SLOP 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 share—basic $ 0.29 $ 0.40 $ 0.08 $ 0.11 Net income attributable to common unitholders per common share—diluted $ 0.29 $ 0.40 $ 0.08 $ 0.11

Organization and Basis of Pre_3

Organization and Basis of Presentation - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018shares
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%
SLG Management LLC | SL Green Management
Organization
Percentage of ownership in SL Green Management LLC owned by operating partnership (percent)	100.00%

Organization and Basis of Pre_4

Organization and Basis of Presentation - Schedule of Commercial Office Properties (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)ft²buildingshares	Dec. 31, 2017USD ($)	Dec. 31, 2015USD ($)
Real estate properties
Number of Properties | building	81
Approximate Square Feet	30,177,253
Weighted Average Occupancy unaudited (as a percent)	92.90%
Investment in mortgage loans on real estate | $	$ 2,099,393	$ 2,114,041	$ 1,640,412
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	69
Approximate Square Feet	27,575,397
Weighted Average Occupancy unaudited (as a percent)	93.10%
Residential
Real estate properties
Number of Properties | building	12
Approximate Square Feet	2,601,856
Weighted Average Occupancy unaudited (as a percent)	91.50%
Managed office properties
Real estate properties
Number of Properties | building	2
Approximate Square Feet	2,100,000
Investment in mortgage loans on real estate | $	$ 2,100,000
Debt investments, other | $	$ 100,000
Consolidated properties
Real estate properties
Number of Properties | building	49
Approximate Square Feet	15,992,145
Consolidated properties | Commercial properties
Real estate properties
Number of Properties | building	47
Approximate Square Feet	15,547,040
Consolidated properties | Residential
Real estate properties
Number of Properties | building	2
Approximate Square Feet	445,105
Unconsolidated properties
Real estate properties
Number of Properties | building	32
Approximate Square Feet	14,185,108
Unconsolidated properties | Commercial properties
Real estate properties
Number of Properties | building	22
Approximate Square Feet	12,028,357
Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	10
Approximate Square Feet	2,156,751
Manhattan
Real estate properties
Number of Properties | building	54
Approximate Square Feet	25,227,197
Weighted Average Occupancy unaudited (as a percent)	93.20%
Manhattan | Office
Real estate properties
Number of Properties | building	30
Approximate Square Feet	23,716,274
Weighted Average Occupancy unaudited (as a percent)	94.50%
Manhattan | Retail
Real estate properties
Number of Properties | building	16
Approximate Square Feet	677,822
Weighted Average Occupancy unaudited (as a percent)	96.70%
Manhattan | Development/Redevelopment
Real estate properties
Number of Properties | building	7
Approximate Square Feet	833,101
Weighted Average Occupancy unaudited (as a percent)	54.10%
Manhattan | Fee Interest
Real estate properties
Number of Properties | building	1
Approximate Square Feet	0
Weighted Average Occupancy unaudited (as a percent)	0.00%
Manhattan | Residential
Real estate properties
Number of Properties | building	12
Approximate Square Feet	2,601,856
Weighted Average Occupancy unaudited (as a percent)	91.50%
Manhattan | Consolidated properties
Real estate properties
Number of Properties | building	32
Approximate Square Feet	13,198,840
Manhattan | Consolidated properties | Office
Real estate properties
Number of Properties | building	20
Approximate Square Feet	12,387,091
Manhattan | Consolidated properties | Retail
Real estate properties
Number of Properties | building	7
Approximate Square Feet	325,648
Manhattan | Consolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	5
Approximate Square Feet	486,101
Manhattan | Consolidated properties | Fee Interest
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0
Manhattan | Consolidated properties | Residential
Real estate properties
Number of Properties | building	2
Approximate Square Feet	445,105
Manhattan | Consolidated properties | Dual property type, retail portion
Real estate properties
Approximate Square Feet	270,132
Manhattan | Consolidated properties | Dual property type, residential portion
Real estate properties
Approximate Square Feet	222,855
Manhattan | Unconsolidated properties
Real estate properties
Number of Properties | building	22
Approximate Square Feet	12,028,357
Manhattan | Unconsolidated properties | Office
Real estate properties
Number of Properties | building	10
Approximate Square Feet	11,329,183
Manhattan | Unconsolidated properties | Retail
Real estate properties
Number of Properties | building	9
Approximate Square Feet	352,174
Manhattan | Unconsolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	2
Approximate Square Feet	347,000
Manhattan | Unconsolidated properties | Fee Interest
Real estate properties
Number of Properties | building	1
Approximate Square Feet	0
Manhattan | Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	10
Approximate Square Feet	2,156,751
Suburban
Real estate properties
Number of Properties | building	15
Approximate Square Feet	2,348,200
Weighted Average Occupancy unaudited (as a percent)	91.40%
Suburban | Office
Real estate properties
Number of Properties | building	13
Approximate Square Feet	2,295,200
Weighted Average Occupancy unaudited (as a percent)	91.30%
Suburban | Retail
Real estate properties
Number of Properties | building	1
Approximate Square Feet	52,000
Weighted Average Occupancy unaudited (as a percent)	100.00%
Suburban | Development/Redevelopment
Real estate properties
Number of Properties | building	1
Approximate Square Feet	1,000
Weighted Average Occupancy unaudited (as a percent)	0.00%
Suburban | Residential
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0
Weighted Average Occupancy unaudited (as a percent)	0.00%
Suburban | Consolidated properties
Real estate properties
Number of Properties | building	15
Approximate Square Feet	2,348,200
Suburban | Consolidated properties | Office
Real estate properties
Number of Properties | building	13
Approximate Square Feet	2,295,200
Suburban | Consolidated properties | Retail
Real estate properties
Number of Properties | building	1
Approximate Square Feet	52,000
Suburban | Consolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	1
Approximate Square Feet	1,000
Suburban | Consolidated properties | Residential
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0
Suburban | Unconsolidated properties
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0
Suburban | Unconsolidated properties | Office
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0
Suburban | Unconsolidated properties | Retail
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0
Suburban | Unconsolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0
Suburban | Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0

Significant Accounting Polici_4

Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Principles of Consolidation
Commercial real estate properties	$ 6,414,798	$ 7,906,006
Mortgages and other loans payable, net	1,961,240	2,837,282
Assets held for sale	0	338,354
Liabilities related to assets held for sale	0	4,074
Consolidated VIEs
Principles of Consolidation
Mortgages and other loans payable, net	$ 140,800	$ 628,900

Significant Accounting Polici_5

Significant Accounting Policies - Investments in Commercial Real Estate Properties (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Real Estate [Line Items]
Depreciation expense (including amortization of the capital lease asset)	$ 242,800,000	$ 365,300,000	$ 783,500,000
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	1 year 9 months 18 days
Weighted average amortization period for below-market leases (in years)	4 years 7 months 6 days
Weighted average amortization for in-place lease costs	5 years 9 months 18 days
Amortization of above and below Market Leases	$ 6,800,000	20,300,000	196,200,000
Reduction in interest expense from amortization of above-market rate mortgages	0	800,000	2,800,000
Identified intangible assets (included in other assets):
Gross amount	266,540,000	325,880,000
Accumulated amortization	(241,040,000)	(277,038,000)
Net	25,500,000	48,842,000
Identified intangible liabilities (included in deferred revenue):
Gross amount	276,245,000	540,283,000
Accumulated amortization	(253,767,000)	(402,583,000)
Net	22,478,000	137,700,000
Net intangible assets reclassed to assets held for sale	0	13,900,000
Net intangible liabilities reclassed to liabilities relates to assets held for sale	0	$ 4,100,000
Other Identifiable Assets
Estimated annual amortization
2,019	9,825,000
2,020	4,817,000
2,021	3,454,000
2,022	1,892,000
2,023	1,507,000
Acquired above-market leases, net of acquired below-market leases
Below Market Lease, Net, Amortization Income, Fiscal Year Maturity [Abstract]
2,019	(5,227,000)
2,020	(3,655,000)
2,021	(1,631,000)
2,022	(1,328,000)
2,023	$ (749,000)
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
388-390 Greenwich Street
Real Estate [Line Items]
Amortization of below market leases			$ 172,400,000

Significant Accounting Polici_6

Significant Accounting Policies - Investment in Marketable Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment in Marketable Securities
Marketable securities	$ 28,638,000	$ 28,579,000
Proceeds from sale of marketable securities	0	55,129,000	$ 6,965,000
Realized gain (loss) on investment in marketable securities		(3,300,000)	$ (100,000)
Fair Value
Investment in Marketable Securities
Marketable securities	28,638,000	28,579,000
Commercial mortgage-backed securities
Investment in Marketable Securities
Marketable securities	28,638,000	28,579,000
Cost basis	27,500,000	27,500,000
Equity marketable securities
Investment in Marketable Securities
Cost basis	$ 0	$ 0

Significant Accounting Polici_7

Significant Accounting Policies - Investments in Unconsolidated Joint Ventures/Deferred Lease Costs/Revenue Recognition/Income Taxes (Details)	12 Months Ended
	Dec. 31, 2018USD ($)joint_venture$ / shares	Dec. 31, 2017USD ($)$ / shares	Dec. 31, 2016USD ($)$ / shares
Schedule of Equity Method Investments [Line Items]
Number of joint ventures with performance guarantees under master leases | joint_venture	1
Deferred Lease Costs [Abstract]
Portion of compensation capitalized	$ 15,700,000	$ 16,400,000	$ 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 loss and other investment reserves, net of recoveries	$ 6,839,000	0	0
Income taxes
Federal, state and local tax provision	2,800,000	4,300,000	2,800,000
Interest Expense Increase (Decrease) Assumed Above Market Rate Mortgage Amortization	$ 0	$ (800,000)	$ (2,800,000)
Dividends per share paid (in dollars per share) | $ / shares	$ 3.25	$ 3.10	$ 2.88
Ordinary Income Dividend
Income taxes
Dividends per share paid (in dollars per share) | $ / shares	1.46	1.24	2.48
Capital Gains Dividend
Income taxes
Dividends per share paid (in dollars per share) | $ / shares	$ 1.79	$ 1.86	$ 0.40

Significant Accounting Polici_8

Significant Accounting Policies - Concentrations of Credit Risk/Reclassification (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)Tenantagreement	Dec. 31, 2017USD ($)	Dec. 31, 2016
Concentration of Credit Risk
Common shares	$ 847	$ 939
Additional paid-in-capital	4,508,685	4,968,338
Treasury shares	(124,049)	(124,049)
Retained earnings	$ 1,278,998	$ 1,139,329
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	6.00%	7.00%	8.80%
Annualized rent | 1185 Avenue of the Americas | Customer concentration
Concentration of Credit Risk
Percentage of concentration	6.70%	7.10%	6.90%
Annualized rent | 11 Madison Avenue | Customer concentration
Concentration of Credit Risk
Percentage of concentration	7.40%	7.10%	6.10%
Annualized rent | 420 Lexington Avenue | Customer concentration
Concentration of Credit Risk
Percentage of concentration	6.50%	6.00%	5.90%
Annualized rent | One Madison Ave | Customer concentration
Concentration of Credit Risk
Percentage of concentration	5.80%	5.60%	5.60%
Collective bargaining arrangements | Workforce concentration
Concentration of Credit Risk
Percentage of concentration	68.70%
Number of collective bargaining agreements | agreement	6
Collective bargaining arrangements expiring in December 2019 | Workforce concentration
Concentration of Credit Risk
Percentage of concentration	56.00%
Tenant 1 | Annualized rent | Customer concentration
Concentration of Credit Risk
Percentage of concentration	8.20%

Significant Accounting Polici_9

Significant Accounting Policies - Accounting Standards Update (Details) - USD ($) $ in Thousands		Jan. 01, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Assets	[1]			$ 12,751,358	$ 13,982,904
Liabilities	[1]			$ 6,115,271	$ 6,629,761
1515 Broadway | Accounting Standards Update 2017-05
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gain on disposal			$ 600,000
Scenario, Forecast | Accounting Standards Update 2018-11
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated decrease in net income		$ 10,000
Minimum | Scenario, Forecast | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Assets		400,000
Liabilities		400,000
Maximum | Scenario, Forecast | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Assets		500,000
Liabilities		$ 500,000
[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: $110.0 million and $398.0 million of land, $0.3 billion and $1.4 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, $42.2 million and $330.9 million of accumulated depreciation, $721.3 million and $221.0 million of other assets included in other line items, $140.8 million and $628.9 million of real estate debt, net, $0.4 million and $2.5 million of accrued interest payable, $43.6 million and $42.8 million of capital lease obligations, and $18.4 million and $56.8 million of other liabilities included in other line items as of December 31, 2018 and December 31, 2017, respectively.

Property Acquisitions - 2018 Ac

Property Acquisitions - 2018 Acquisitions (Details) $ in Millions	1 Months Ended
	Dec. 31, 2018USD ($)ft²	Nov. 30, 2018ft²	Oct. 31, 2018USD ($)ft²	Aug. 31, 2018USD ($)aparcel	Jul. 31, 2018USD ($)ft²	May 31, 2018USD ($)ft²
Business Acquisition [Line Items]
Approximate Square Feet | ft²	30,177,253
2 Herald Square
Business Acquisition [Line Items]
Approximate Square Feet | ft²						369,000
Acquisition Price (in millions) | $						$ 266
Purchase price fair value adjustment | $						$ 8.1
1231 Third Avenue
Business Acquisition [Line Items]
Approximate Square Feet | ft²					39,000
Acquisition Price (in millions) | $					$ 55.4
Upper East Side Residential
Business Acquisition [Line Items]
Approximate Square Feet | a				0.2
Acquisition Price (in millions) | $				$ 30.2
Number of land parcels, fee interest acquired | parcel				3
113 Greene Street
Business Acquisition [Line Items]
Approximate Square Feet | ft²			6,425
Acquisition Price (in millions) | $			$ 31
712 Madison Avenue
Business Acquisition [Line Items]
Approximate Square Feet | ft²	6,600
Acquisition Price (in millions) | $	$ 58
2 Herald Square
Business Acquisition [Line Items]
Approximate Square Feet | ft²		369,000
Ownership percentage in disposed asset		49.00%

Property Acquisitions - 2016 Ac

Property Acquisitions - 2016 Acquisitions (Details) - 183 Broadway - USD ($) $ in Thousands	1 Months Ended
	Mar. 31, 2016	Mar. 31, 2017
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

Properties Held for Sale and _3

Properties Held for Sale and Property Dispositions (Details) $ in Thousands

1 Months Ended

12 Months Ended

Nov. 30, 2018USD ($)ft²a

Jun. 30, 2018USD ($)ft²

May 31, 2018USD ($)ft²

Feb. 22, 2018

Jan. 31, 2018USD ($)

Dec. 31, 2017USD ($)

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, 2018USD ($)ft²

Feb. 28, 2018USD ($)

Jan. 01, 2018USD ($)ft²

Dec. 31, 2016USD ($)

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

30,177,253

Employee-related liabilities

$ 0

$ 11,700

$ 1,100

2 Herald Square

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

369,000

Gross asset valuation

$ 265,000

Gain on Sale

$ 0

Ownership percentage in disposed asset

49.00%

400 Summit Lake Drive

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | a

39.5

Gross asset valuation

$ 3,000

Gain on Sale

$ (36,200)

Upper East Side Assemblage

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

70,142

Gross asset valuation

$ 143,800

Gain on Sale

$ (6,300)

Impairment charge

$ 5,800

1-6 International Drive

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

540,000

Gross asset valuation

$ 55,000

Gain on Sale

$ (2,600)

635 Madison Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

176,530

Gross asset valuation

$ 153,000

Gain on Sale

$ (14,100)

115-117 Stevens Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

178,000

Gross asset valuation

$ 12,000

Gain on Sale

$ (700)

600 Lexington Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

303,515

Gross asset valuation

$ 305,000

Gain on Sale

$ 23,800

Employee-related liabilities

$ 1,300

1515 Broadway

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

1,750,000

Gross asset valuation

$ 1,950,000

$ 1,950,000

Gain on Sale

$ 0

Joint venture ownership percentage sold

12.87%

30.13%

125 Chubb Way

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

278,000

Gross asset valuation

$ 29,500

Gain on Sale

$ (26,100)

16 Court Street

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

317,600

Gross asset valuation

$ 171,000

Gain on Sale

64,900

Employee-related liabilities

$ 2,500

680-750 Washington Boulevard

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

325,000

Gross asset valuation

$ 97,000

Gain on Sale

$ (44,200)

520 White Plains Road

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

180,000

Gross asset valuation

$ 21,000

Gain on Sale

$ (14,600)

102 Greene Street

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

9,200

Gross asset valuation

$ 43,500

$ 43,500

Gain on Sale

4,900

Employee-related liabilities

$ 900

Joint venture ownership percentage sold

10.00%

90.00%

400 East 57th Street

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

290,482

Gross asset valuation

$ 83,300

Gain on Sale

23,900

Employee-related liabilities

$ 1,000

Ownership percentage in disposed asset

49.00%

11 Madison Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

2,314,000

Gross asset valuation

$ 2,605,000

Gain on Sale

3,600

Employee-related liabilities

$ 600

Ownership percentage in disposed asset

40.00%

500 West Putnam Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

121,500

Gross asset valuation

$ 41,000

Gain on Sale

$ (10,400)

388 Greenwich

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

2,635,000

Gross asset valuation

$ 2,002,300

Gain on Sale

206,500

Employee-related liabilities

$ 1,600

7 International Drive

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | a

31

Gross asset valuation

$ 20,000

Gain on Sale

$ (6,900)

248-252 Bedford Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

66,611

Gross asset valuation

$ 55,000

Gain on Sale

15,300

Employee-related liabilities

$ 1,300

885 Third Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

607,000

Gross asset valuation

$ 453,000

Gain on Sale

$ (8,800)

Debt and Preferred Equity Inv_3

Debt and Preferred Equity Investments - Roll Forward of Net Book Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at beginning of period	$ 2,114,041		$ 1,640,412
Redemptions/sales/syndications/amortization	(994,906)		(813,418)
Net change in loan loss reserves		$ (5,750)	0
Balance at end of period	2,099,393	$ 2,114,041
Debt investment
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Originations/accretion	834,304		1,142,591
Preferred equity investments
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Originations/accretion	$ 151,704		$ 144,456

Debt and Preferred Equity Inv_4

Debt and Preferred Equity Investments - Rollforward of Total Allowance for Loan Loss Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loan loss reserve activity
Balance at beginning of year	$ 0	$ 0	$ 0
Expensed	6,839	0	0
Recoveries	0	0	0
Charge-offs and reclassifications	(1,089)	0	0
Balance at end of year	$ 5,750	$ 0	$ 0

Debt and Preferred Equity Inv_5

Debt and Preferred Equity Investments - Debt Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Mortgage loans on real estate, interest rate	8.99%
Debt Investments Held [Abstract]
Carrying value	$ 2,099,393	$ 2,114,041
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 2019
Debt Investments Held [Abstract]
Amount participated out	14,600
Mezzanine Loan With An Initial Maturity Date Of March 2019, 3
Debt Investments Held [Abstract]
Amount participated out	14,100
Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Amount participated out	1,300
Debt investment
Debt Investments Held [Abstract]
Future Funding Obligations	156,293
Senior Financing	6,713,884
Carrying value	1,812,936	1,969,618
Total fixed rate
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	4,129,847
Carrying Value	430,099	669,968
Total fixed rate | Mezzanine Loan With An Initial Maturity Of August 2022
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	280,000
Carrying Value	36,585	34,600
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	24,932	24,913
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of November 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	85,097
Carrying Value	12,706	12,699
Total fixed rate | Mezzanine Loan With An Initial Maturity Date Of December 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	180,000
Carrying Value	30,000	0
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	12,941	12,932
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	11,000	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	1,712,750
Carrying Value	55,250	55,250
Total fixed rate | Mortgage and Jr Mortgage loan satisfied via foreclosure
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	250,464
Total fixed rate | Mezzanine Loan Repaid In August 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	26,366
Total fixed rate | Mortgage Loan Repaid In September 2018 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	239
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	213,185	204,005
Total floating rate
Debt Investments Held [Abstract]
Future Funding Obligations	156,293
Senior Financing	2,584,037
Carrying value	1,382,837	1,299,650
Total floating rate | Mezzanine Loan with an Initial Maturity Date of January 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	45,025
Carrying value	37,499	34,879
Total floating rate | Mezzanine Loan with an Initial Maturity of March 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	85,000
Carrying value	15,333	15,381
Total floating rate | Mezzanine Loan With An Initial Maturity Date Of March 2019, 3
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	65,000
Carrying value	14,822	14,869
Total floating rate | Mezzanine Loan with an Initial Maturity of March 2019, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	38,000
Carrying value	21,990	21,939
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000
Carrying value	19,986	19,982
Total floating rate | Mezzanine Loan With An Initial Maturity Date Of April 2019, 4
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	265,000
Carrying value	24,961	24,830
Total floating rate | Mortgage/Jr Mortgage Participate Loan, Maturity Date of August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	40,530
Senior Financing	233,086
Carrying value	84,012	71,832
Total floating rate | Mezzanine Loan With An Initial Maturity Date Of August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	65,000
Carrying value	14,998	14,955
Total floating rate | Mortgage/Mezzanine Loan With An Initial Maturity Date Of August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	19,999	19,940
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of September 2019
Debt Investments Held [Abstract]
Future Funding Obligations	1,027
Senior Financing	0
Carrying value	154,070	143,919
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	34,886	34,737
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	7,243
Senior Financing	0
Carrying value	62,493	43,845
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	559
Senior Financing	575,955
Carrying value	79,164	75,834
Total floating rate | Mortgage Loan with an Initial Maturity of February 2020
Debt Investments Held [Abstract]
Future Funding Obligations	11,204
Senior Financing	0
Carrying value	88,501	0
Total floating rate | Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Future Funding Obligations	1,277
Senior Financing	322,300
Carrying value	53,402	0
Total floating rate | Mortgage and Mezzanine Loan with an Initial Maturity Date of April 2020
Debt Investments Held [Abstract]
Future Funding Obligations	14,860
Senior Financing	0
Carrying value	277,694	0
Total floating rate | Mortgage And Mezzanine Loan With An Initial Maturity Date Of June 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	37,094	0
Total floating rate | Mezzanine Loan with an Initial Maturity of July 2020
Debt Investments Held [Abstract]
Future Funding Obligations	7,887
Senior Financing	38,167
Carrying value	12,627	11,259
Total floating rate | Mortgage And Mezzanine Loan With An Initial Maturity Date Of October 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	83,449	0
Total floating rate | Mezzanine Loan with an Initial Maturity of November 2020
Debt Investments Held [Abstract]
Future Funding Obligations	38,575
Senior Financing	362,908
Carrying value	88,817	75,428
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of December 2020
Debt Investments Held [Abstract]
Future Funding Obligations	33,131
Senior Financing	0
Carrying value	98,804	88,989
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of December 2020, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	35,266	35,152
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	15,665	15,635
Total floating rate | Mezzanine Loan With An Initial Maturity Date Of December 2021
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	38,596
Carrying value	7,305	34,947
Total floating rate | Mortgage/Mezzanine Loan Repaid In February 2018, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	162,553
Total floating rate | Mortgage/Mezzanine Loan repaid in February 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	74,755
Total floating rate | Mezzanine Loan Sold In 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	23,609
Total floating rate | Mortgage And Mezzanine Loan Repaid In 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	16,969
Total floating rate | Mezzanine Loan Repaid In 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	59,723
Total floating rate | Mezzanine Loan Repaid In 2018, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	37,851
Total floating rate | Mezzanine Loan Repaid In 2018, 3
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	14,855
Total floating rate | Mezzanine Loan Exchanged For Property In 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	12,174
Total floating rate | Mezzanine Loan Exchanged For Property In 2018, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	10,934
Total floating rate | Mezzanine Loan Repaid In 2018, 4
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	37,250
Total floating rate | Mezzanine Loan Repaid In 2018, 5
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	15,148
Total floating rate | Mezzanine Loan Repaid In 2018, 6
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	8,550
Total floating rate | Mezzanine Loan Exchanged For Property In 2018, 3
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	$ 0	$ 26,927

Debt and Preferred Equity Inv_6

Debt and Preferred Equity Investments - Preferred Equity Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Preferred equity investment
Mortgage loans on real estate, interest rate	8.99%
Carrying value	$ 2,099,393	$ 2,114,041
Preferred Equity, April 2021
Preferred equity investment
Future Funding Obligations	0
Senior Financing	272,000
Carrying value	143,183	144,423
Preferred Equity Redeemed in May 2017
Preferred equity investment
Future Funding Obligations	0
Senior Financing	1,768,000
Carrying value	$ 143,274	0
Preferred equity investments
Preferred equity investment
Mortgage loans on real estate, interest rate	9.12%
Future Funding Obligations	$ 0
Senior Financing	2,040,000
Carrying value	$ 286,457	$ 144,423

Debt and Preferred Equity Inv_7

Debt and Preferred Equity Investments - Narrative (Details)	1 Months Ended	12 Months Ended
	Sep. 30, 2014USD ($)	Dec. 31, 2018USD ($)loansegment	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Preferred equity investment
Allowance for loan and lease losses		$ 5,750,000	$ 0	$ 0	$ 0
Number of investments marketed for sale | loan		2
Unpaid principal balance		$ 159,900,000
Carrying value		$ 2,099,393,000	$ 2,114,041,000
Number of portfolio segments of financial receivables (segment) | segment		1	1
Additional amount of financing receivables included in other assets		$ 88,800,000	$ 65,500,000
Financing receivable, nonaccrual status		$ 28,400,000
Weighted average risk rating		1.2
Junior Mortgage Participation Acquired in September 2014
Preferred equity investment
Payments to acquire loans receivable	$ 0
Carrying value			$ 0
Financing Receivables, Equal to Greater than 90 Days Past Due
Preferred equity investment
Financing receivable, past due		$ 0

Investments in Unconsolidated_3

Investments in Unconsolidated Joint Ventures - Additional Information (Details) $ in Thousands	Jan. 01, 2018USD ($)	Jan. 31, 2019USD ($)	Feb. 28, 2018	Feb. 22, 2018	Nov. 30, 2017	Oct. 31, 2016ft²	Aug. 31, 2016ft²	Mar. 31, 2018property	Dec. 31, 2018USD ($)ft²unit	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)ft²unit	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2017USD ($)
General information on each joint venture
Investments in unconsolidated joint ventures									$ 3,019,020				$ 3,019,020	$ 2,362,989
Net equity investment in VIEs									$ 808,300				$ 808,300	606,200
Approximate Square Feet | ft²									30,177,253				30,177,253
Purchase price and other fair value adjustment									$ 0	$ (3,057)	$ 11,149	$ 49,293	$ 57,385	$ 0	$ 0
11 Madison Avenue
General information on each joint venture
Approximate Square Feet | ft²							2,314,000
Ownership percentage in disposed asset							40.00%
400 East 57th Street
General information on each joint venture
Approximate Square Feet | ft²						290,482
Ownership percentage in disposed asset						49.00%
21 East 66th Street | Three Retail and Two Residential Units
General information on each joint venture
Ownership Interest Sold									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 Sold									16.14%				16.14%
Number of residential units | unit									3				3
Stonehenge Portfolio
General information on each joint venture
Ownership Interest Sold						90.00%
Disposal group, number of properties | property								2
400 East 57th Street
General information on each joint venture
Ownership Interest Sold									51.00%				51.00%
One Vanderbilt
General information on each joint venture
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																23.40%
1515 Broadway
General information on each joint venture
Gain on disposal	$ 600,000
1552 Broadway
General information on each joint venture
Approximate Square Feet | ft²									13,045				13,045
Joint venture
General information on each joint venture
Investments in unconsolidated joint ventures									$ 3,019,020				$ 3,019,020
Equity method investments with negative book value									$ 85,800				$ 85,800
Joint venture | 100 Park Avenue
General information on each joint venture
Ownership Interest Sold									49.90%				49.90%
Economic Interest, percent									49.90%				49.90%
Approximate Square Feet | ft²									834,000				834,000
Acquisition Price									$ 95,800				$ 95,800
Joint venture | 717 Fifth Avenue
General information on each joint venture
Ownership Interest Sold									10.92%				10.92%
Approximate Square Feet | ft²									119,500				119,500
Acquisition Price									$ 251,900				$ 251,900
Joint venture | 800 Third Avenue
General information on each joint venture
Ownership Interest Sold									60.52%				60.52%
Economic Interest, percent									60.52%				60.52%
Approximate Square Feet | ft²									526,000				526,000
Acquisition Price									$ 285,000				$ 285,000
Joint venture | 919 Third Avenue
General information on each joint venture
Ownership Interest Sold									51.00%				51.00%
Economic Interest, percent									51.00%				51.00%
Approximate Square Feet | ft²									1,454,000				1,454,000
Acquisition Price									$ 1,256,727				$ 1,256,727
Joint venture | 11 West 34th Street
General information on each joint venture
Ownership Interest Sold									30.00%				30.00%
Economic Interest, percent									30.00%				30.00%
Approximate Square Feet | ft²									17,150				17,150
Acquisition Price									$ 10,800				$ 10,800
Joint venture | 280 Park Avenue
General information on each joint venture
Ownership Interest Sold									50.00%				50.00%
Economic Interest, percent									50.00%				50.00%
Approximate Square Feet | ft²									1,219,158				1,219,158
Acquisition Price									$ 400,000				$ 400,000
Joint venture | 1552-1560 Broadway
General information on each joint venture
Ownership Interest Sold									50.00%				50.00%
Economic Interest, percent									50.00%				50.00%
Approximate Square Feet | ft²									57,718				57,718
Acquisition Price									$ 136,550				$ 136,550
Joint venture | 10 East 53rd Street
General information on each joint venture
Ownership Interest Sold									55.00%				55.00%
Economic Interest, percent									55.00%				55.00%
Approximate Square Feet | ft²									354,300				354,300
Acquisition Price									$ 252,500				$ 252,500
Joint venture | 521 Fifth Avenue
General information on each joint venture
Ownership Interest Sold									50.50%				50.50%
Economic Interest, percent									50.50%				50.50%
Approximate Square Feet | ft²									460,000				460,000
Acquisition Price									$ 315,000				$ 315,000
Joint venture | 21 East 66th Street
General information on each joint venture
Ownership Interest Sold									32.28%				32.28%
Economic Interest, percent									32.28%				32.28%
Approximate Square Feet | ft²									13,069				13,069
Acquisition Price									$ 75,000				$ 75,000
Joint venture | 650 Fifth Avenue
General information on each joint venture
Ownership Interest Sold									50.00%				50.00%
Approximate Square Feet | ft²									69,214				69,214
Acquisition Price									$ 0				$ 0
Joint venture | 121 Greene Street
General information on each joint venture
Ownership Interest Sold									50.00%				50.00%
Economic Interest, percent									50.00%				50.00%
Approximate Square Feet | ft²									7,131				7,131
Acquisition Price									$ 27,400				$ 27,400
Joint venture | 55 West 46th Street
General information on each joint venture
Ownership Interest Sold									25.00%				25.00%
Economic Interest, percent									25.00%				25.00%
Approximate Square Feet | ft²									347,000				347,000
Acquisition Price									$ 295,000				$ 295,000
Joint venture | Stonehenge Portfolio
General information on each joint venture
Ownership Interest Sold						10.00%
Approximate Square Feet | ft²									1,439,016				1,439,016
Acquisition Price									$ 36,668				$ 36,668
Joint venture | 131-137 Spring Street
General information on each joint venture
Ownership Interest Sold									20.00%				20.00%
Economic Interest, percent									20.00%				20.00%
Approximate Square Feet | ft²									68,342				68,342
Acquisition Price									$ 277,750				$ 277,750
Joint venture | 605 West 42nd Street
General information on each joint venture
Ownership Interest Sold									20.00%				20.00%
Economic Interest, percent									20.00%				20.00%
Approximate Square Feet | ft²									927,358				927,358
Acquisition Price									$ 759,000				$ 759,000
Joint venture | 11 Madison Avenue
General information on each joint venture
Ownership Interest Sold									60.00%				60.00%
Economic Interest, percent									60.00%				60.00%
Approximate Square Feet | ft²									2,314,000				2,314,000
Acquisition Price									$ 2,605,000				$ 2,605,000
Joint venture | 333 East 22nd St
General information on each joint venture
Ownership Interest Sold									33.33%				33.33%
Economic Interest, percent									33.33%				33.33%
Approximate Square Feet | ft²									26,926				26,926
Acquisition Price									$ 0				$ 0
Joint venture | 400 East 57th Street
General information on each joint venture
Ownership Interest Sold									51.00%				51.00%
Economic Interest, percent									41.00%				41.00%
Approximate Square Feet | ft²									290,482				290,482
Acquisition Price									$ 170,000				$ 170,000
Joint venture | One Vanderbilt
General information on each joint venture
Ownership Interest Sold									71.01%				71.01%
Economic Interest, percent									71.01%				71.01%
Approximate Square Feet | ft²									0				0
Acquisition Price									$ 3,310,000				$ 3,310,000
Joint venture | Worldwide Plaza
General information on each joint venture
Ownership Interest Sold									24.35%				24.35%
Economic Interest, percent									24.35%				24.35%
Approximate Square Feet | ft²									2,048,725				2,048,725
Acquisition Price									$ 1,725,000				$ 1,725,000
Joint venture | 1515 Broadway
General information on each joint venture
Ownership Interest Sold									56.87%				56.87%
Economic Interest, percent									56.87%				56.87%
Approximate Square Feet | ft²									1,750,000				1,750,000
Acquisition Price									$ 1,950,000				$ 1,950,000
Joint venture | 2 Herald Square
General information on each joint venture
Ownership Interest Sold									51.00%				51.00%
Economic Interest, percent									51.00%				51.00%
Approximate Square Feet | ft²									369,000				369,000
Acquisition Price									$ 266,000				$ 266,000
Allianz Real Estate | 1515 Broadway
General information on each joint venture
Ownership percentage in disposed asset			13.00%	12.87%	30.13%
Subsequent Event | Joint venture | 131-137 Spring Street
General information on each joint venture
Proceeds from sale of interest in property		$ 15,200
919 Third Avenue | Joint venture | 919 Third Avenue
General information on each joint venture
Purchase price and other fair value adjustment													$ 49,300

Investments in Unconsolidated_4

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
	Nov. 30, 2018USD ($)	Jul. 31, 2018USD ($)	Jun. 30, 2018USD ($)	May 31, 2018USD ($)	Apr. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Feb. 28, 2018USD ($)	May 31, 2017USD ($)	Sep. 30, 2016USD ($)	May 31, 2016USD ($)	Mar. 31, 2016USD ($)	Feb. 29, 2016USD ($)	Dec. 31, 2018USD ($)ft²note	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2018USD ($)ft²note	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Aug. 31, 2018USD ($)	Apr. 30, 2017USD ($)ft²	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures													$ 3,019,020				$ 2,362,989					$ 3,019,020	$ 2,362,989
Acquisition, development and construction arrangements, carrying value													44,357				171,539					44,357	171,539
Gain (Loss) on Sale													167,445	$ 70,937	$ 72,025	$ (6,440)	0	$ 1,030	$ 13,089	$ 2,047		303,967	16,166	$ 44,009
Employee-related liabilities													$ 11,700				0					$ 11,700	0	1,100
Approximate Square Feet | ft²													30,177,253									30,177,253
Gain on sale of real estate, net													$ (36,984)	$ (2,504)	$ (14,790)	$ 23,521	76,497	$ 0	$ (3,823)	$ 567		$ (30,757)	73,241	$ 238,116
Participating Financing Due February 2022
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures													44,357				44,823					44,357	44,823
Mezzanine Loan And Preferred Equity, Due March 2018
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures													0				100,000					0	100,000
Mezzanine Loan Due July 2036
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures													0				$ 26,716					0	$ 26,716
747 Madison Avenue
Schedule of Equity Method Investments [Line Items]
Gain on sale of real estate, net								$ 13,000
3 Columbus Circle
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold	48.90%
Gross asset valuation	$ 851,000
Gain (Loss) on Sale	$ 160,368
Mezzanine Loan
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold																									33.33%
Gross asset valuation																									$ 15,000
724 Fifth Avenue
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold		49.90%
Gross asset valuation		$ 365,000
Gain (Loss) on Sale		$ 64,587
Jericho Plaza
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold			11.67%								11.67%				11.67%												77.78%
Gross asset valuation			$ 117,400												$ 117,400
Gain (Loss) on Sale			$ 147
1745 Broadway
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold				56.87%
Gross asset valuation				$ 633,000
Gain (Loss) on Sale				$ 52,038
175-225 Third Street Brooklyn, New York
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold					95.00%
Gross asset valuation					$ 115,000
Gain (Loss) on Sale					$ 19,483
Stonehenge Portfolio
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold						0.50%										0.50%
Gross asset valuation						$ 287,000										$ 287,000
Gain (Loss) on Sale						$ (5,701)
1515 Broadway
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold							13.00%
Gross asset valuation							$ 1,950,000						$ 1,950,000									$ 1,950,000
Gain (Loss) on Sale							$ 0
Approximate Square Feet | ft²													1,750,000									1,750,000
1274 Fifth Avenue
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold							9.83%
Gross asset valuation							$ 44,100
Gain (Loss) on Sale							$ (362)
102 Greene Street
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold																		10.00%			10.00%
Gross asset valuation																		$ 43,500			$ 43,500					$ 43,500
Gain (Loss) on Sale																					$ 283
Employee-related liabilities																										$ 900
Approximate Square Feet | ft²																										9,200
76 11th Avenue
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold								33.33%
Gross asset valuation								$ 138,240
Number of notes owned | note													2									2
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 Sold																		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 Sold										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 Sold																				4.79%
Gross asset valuation																				$ 180,700
Gain (Loss) on Sale											$ 2,800
7 Renaissance
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold																				50.00%
Gross asset valuation																				$ 20,700
Gain (Loss) on Sale											$ 4,200
1 Jericho
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold												66.11%
Gross asset valuation												$ 95,200
Gain (Loss) on Sale												$ 3,300
Joint venture
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures													$ 3,019,020									$ 3,019,020

Investments in Unconsolidated_5

Investments in Unconsolidated Joint Ventures - Mortgages and Other Loans Payable (Details)	12 Months Ended
	Dec. 31, 2018USD ($)extension	Dec. 31, 2017USD ($)	Oct. 31, 2016
Debt Instrument [Line Items]
Long-term debt	$ 1,961,240,000	$ 2,837,282,000
Total fixed rate debt	1,389,717,000	2,400,560,000
Total floating rate debt	598,442,000	465,431,000
Total fixed rate and floating rate debt	1,988,159,000	2,865,991,000
Deferred financing costs, net	(26,919,000)	(28,709,000)
919 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 0	500,000,000
400 East 57th Street
Debt Instrument [Line Items]
Ownership Interest Sold	51.00%
Stonehenge Portfolio
Debt Instrument [Line Items]
Ownership Interest Sold			90.00%
Joint venture
Debt Instrument [Line Items]
Total fixed rate debt	$ 5,666,108,000	5,569,138,000
Total floating rate debt	3,387,705,000	3,979,066,000
Total fixed rate and floating rate debt	9,053,813,000	9,548,204,000
Deferred financing costs, net	(103,191,000)	(136,103,000)
Total joint venture mortgages and other loans payable, net	8,950,622,000	9,412,101,000
Joint venture | 1745 Broadway
Debt Instrument [Line Items]
Total floating rate debt	$ 0	345,000,000
Joint venture | 521 Fifth Avenue
Debt Instrument [Line Items]
Economic Interest, percent	50.50%
Interest rate, fixed rate debt (as a percent)	3.73%
Total fixed rate debt	$ 170,000,000	170,000,000
Ownership Interest Sold	50.50%
Joint venture | 717 Fifth Avenue
Debt Instrument [Line Items]
Ownership Interest Sold	10.92%
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]
Economic Interest, percent	10.92%
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]
Economic Interest, percent	32.28%
Interest rate, fixed rate debt (as a percent)	3.60%
Total fixed rate debt	$ 12,000,000	12,000,000
Total floating rate debt	$ 1,571,000	1,648,000
Ownership Interest Sold	32.28%
Joint venture | 919 Third Avenue
Debt Instrument [Line Items]
Economic Interest, percent	51.00%
Interest rate, fixed rate debt (as a percent)	5.12%
Total fixed rate debt	$ 500,000,000	0
Ownership Interest Sold	51.00%
Joint venture | 1515 Broadway
Debt Instrument [Line Items]
Economic Interest, percent	56.87%
Interest rate, fixed rate debt (as a percent)	3.93%
Total fixed rate debt	$ 855,876,000	872,528,000
Ownership Interest Sold	56.87%
Joint venture | 11 Madison Avenue
Debt Instrument [Line Items]
Economic Interest, percent	60.00%
Interest rate, fixed rate debt (as a percent)	3.84%
Total fixed rate debt	$ 1,400,000,000	1,400,000,000
Ownership Interest Sold	60.00%
Joint venture | 800 Third Avenue
Debt Instrument [Line Items]
Economic Interest, percent	60.52%
Interest rate, fixed rate debt (as a percent)	3.37%
Total fixed rate debt	$ 177,000,000	177,000,000
Ownership Interest Sold	60.52%
Joint venture | 400 East 57th Street
Debt Instrument [Line Items]
Economic Interest, percent	41.00%
Interest rate, fixed rate debt (as a percent)	3.00%
Total fixed rate debt	$ 99,828,000	100,000,000
Ownership Interest Sold	51.00%
Joint venture | Worldwide Plaza
Debt Instrument [Line Items]
Economic Interest, percent	24.35%
Interest rate, fixed rate debt (as a percent)	3.98%
Total fixed rate debt	$ 1,200,000,000	1,200,000,000
Ownership Interest Sold	24.35%
Joint venture | Stonehenge Portfolio
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.20%
Total fixed rate debt	$ 321,076,000	357,282,000
Ownership Interest Sold			10.00%
Joint venture | Stonehenge Portfolio | Initial Maturity August 2019
Debt Instrument [Line Items]
Total fixed rate debt	134,300,000
Joint venture | Stonehenge Portfolio | Initial Maturity June 2024
Debt Instrument [Line Items]
Total fixed rate debt	54,100,000
Joint venture | Stonehenge Portfolio | Secured Debt, Initial Maturity April 2028
Debt Instrument [Line Items]
Total fixed rate debt	132,600,000
Joint venture | 3 Columbus Circle
Debt Instrument [Line Items]
Total fixed rate debt	0	350,000,000
Joint venture | Jericho Plaza
Debt Instrument [Line Items]
Total floating rate debt	$ 0	81,099,000
Joint venture | 280 Park Avenue
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Interest rate, floating rate debt (as a percent)	1.73%
Total floating rate debt	$ 1,200,000,000	1,200,000,000
Ownership Interest Sold	50.00%
Joint venture | 10 East 53rd Street
Debt Instrument [Line Items]
Economic Interest, percent	55.00%
Interest rate, floating rate debt (as a percent)	2.25%
Total floating rate debt	$ 170,000,000	170,000,000
Ownership Interest Sold	55.00%
Joint venture | 724 Fifth Avenue
Debt Instrument [Line Items]
Total floating rate debt	$ 0	275,000,000
Joint venture | 55 West 46th Street
Debt Instrument [Line Items]
Economic Interest, percent	25.00%
Interest rate, floating rate debt (as a percent)	2.13%
Total floating rate debt	$ 185,569,000	171,444,000
Committed amount	195,000,000
Unused borrowing capacity, amount	$ 9,400,000
Ownership Interest Sold	25.00%
Joint venture | 175-225 Third Street Brooklyn, New York
Debt Instrument [Line Items]
Total floating rate debt	$ 0	40,000,000
Joint venture | 605 West 42nd Street
Debt Instrument [Line Items]
Economic Interest, percent	20.00%
Total floating rate debt	$ 550,000,000	550,000,000
Ownership Interest Sold	20.00%
Joint venture | 650 Fifth Avenue
Debt Instrument [Line Items]
Ownership Interest Sold	50.00%
Joint venture | 650 Fifth Avenue | Mortgage loan
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Interest rate, fixed rate debt (as a percent)	4.46%
Long-term debt	$ 210,000,000
Total fixed rate debt	$ 210,000,000	210,000,000
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	65,000,000
Joint venture | 650 Fifth Avenue | Mezzanine Loan, Initial Maturity October 2022 | Mezzanine loans
Debt Instrument [Line Items]
Long-term debt	$ 65,000,000
Joint venture | 121 Greene Street
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Interest rate, floating rate debt (as a percent)	1.50%
Total floating rate debt	$ 15,000,000	15,000,000
Ownership Interest Sold	50.00%
Joint venture | 131-137 Spring Street
Debt Instrument [Line Items]
Economic Interest, percent	20.00%
Interest rate, floating rate debt (as a percent)	1.55%
Total floating rate debt	$ 141,000,000	141,000,000
Ownership Interest Sold	20.00%
Joint venture | 1552-1560 Broadway
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Interest rate, floating rate debt (as a percent)	2.65%
Total floating rate debt	$ 195,000,000	195,000,000
Ownership Interest Sold	50.00%
Joint venture | 11 West 34th Street
Debt Instrument [Line Items]
Economic Interest, percent	30.00%
Interest rate, floating rate debt (as a percent)	1.45%
Total floating rate debt	$ 23,000,000	23,000,000
Ownership Interest Sold	30.00%
Joint venture | 103 East 86th Street
Debt Instrument [Line Items]
Economic Interest, percent	1.00%
Interest rate, floating rate debt (as a percent)	1.40%
Total floating rate debt	$ 38,000,000	55,340,000
Joint venture | 100 Park Avenue
Debt Instrument [Line Items]
Economic Interest, percent	49.90%
Interest rate, floating rate debt (as a percent)	1.75%
Total floating rate debt	$ 360,000,000	360,000,000
Ownership Interest Sold	49.90%
Joint venture | One Vanderbilt
Debt Instrument [Line Items]
Economic Interest, percent	71.01%
Interest rate, floating rate debt (as a percent)	2.75%
Total floating rate debt	$ 375,000,000	355,535,000
Ownership Interest Sold	71.01%
Joint venture | One Vanderbilt | Construction Loans
Debt Instrument [Line Items]
Maximum facility capacity	$ 1,750,000,000
Initial Term (in Years)	5 years
Number of extension options | extension	2
Period of extension option	1 year
Joint venture | 2 Herald Square
Debt Instrument [Line Items]
Economic Interest, percent	51.00%
Interest rate, floating rate debt (as a percent)	1.55%
Total floating rate debt	$ 133,565,000	$ 0
Committed amount	$ 150,000,000
Ownership Interest Sold	51.00%
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)
Joint venture | Weighted Average | 605 West 42nd Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.44%

Investments in Unconsolidated_6

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment in Unconsolidated Joint Ventures
Management fees, base revenue									$ 113,596	$ 172,939	$ 196,858
Assets
Commercial real estate property, net	$ 6,414,798				$ 7,906,006				6,414,798	7,906,006
Cash and cash equivalents	129,475				127,888				129,475	127,888
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	41,589				57,644				41,589	57,644
Debt and preferred equity investments	2,099,393				2,114,041				2,099,393	2,114,041
Other assets	295,679				310,688				295,679	310,688
Liabilities and equity
Mortgages and other loans payable, net	1,961,240				2,837,282				1,961,240	2,837,282
Deferred revenue	94,453				208,119				94,453	208,119
Other liabilities	116,566				188,005				116,566	188,005
Company's investments in unconsolidated joint ventures	3,019,020				2,362,989				3,019,020	2,362,989
Combined statements of income for the unconsolidated joint ventures
Real estate taxes									186,351	244,323	248,388
Ground rent									32,965	33,231	33,261
Interest expense, net of interest income									208,669	257,045	321,199
Amortization of deferred financing costs									12,408	16,498	24,564
Transaction related costs									1,099	(1,834)	7,528
Depreciation and amortization									279,507	403,320	821,041
Total expenses	267,678	$ 265,553	$ 258,303	$ 258,282	314,108	$ 333,913	$ 365,749	$ 332,675	1,049,816	1,346,445	1,868,599
Company's equity in net income from unconsolidated joint ventures (1)	(2,398)	$ 971	$ 4,702	$ 4,036	7,788	$ 4,078	$ 3,412	$ 6,614	7,311	21,892	11,874
Joint venture
Assets
Commercial real estate property, net	14,347,673				12,822,133				14,347,673	12,822,133
Cash and cash equivalents	381,301				494,909				381,301	494,909
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	273,141				349,944				273,141	349,944
Debt and preferred equity investments	44,357				202,539				44,357	202,539
Other assets	2,187,166				1,407,806				2,187,166	1,407,806
Total assets	17,233,638				15,277,331				17,233,638	15,277,331
Liabilities and equity
Mortgages and other loans payable, net	8,950,622				9,412,101				8,950,622	9,412,101
Deferred revenue	1,660,838				985,648				1,660,838	985,648
Other liabilities	946,313				411,053				946,313	411,053
Equity	5,675,865				4,468,529				5,675,865	4,468,529
Total liabilities and equity	17,233,638				$ 15,277,331				17,233,638	15,277,331
Company's investments in unconsolidated joint ventures	$ 3,019,020								3,019,020
Combined statements of income for the unconsolidated joint ventures
Total revenues									1,244,804	904,230	712,689
Operating expenses									219,440	157,610	126,913
Real estate taxes									226,961	142,774	111,673
Ground rent									18,697	16,794	14,924
Interest expense, net of interest income									363,055	250,063	197,741
Amortization of deferred financing costs									21,634	23,026	24,829
Transaction related costs									0	146	5,566
Depreciation and amortization									421,458	279,419	199,011
Total expenses									1,271,245	869,832	680,657
Loss on early extinguishment of debt									0	(7,899)	(1,606)
Net (loss) income before gain on sale (1)									(26,441)	26,499	30,426
Company's equity in net income from unconsolidated joint ventures (1)									7,311	21,892	11,874
Management Service, Base | Joint venture
Investment in Unconsolidated Joint Ventures
Management fees, base revenue									$ 14,200	$ 22,600	$ 4,000

Deferred Costs (Details)

Deferred Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred leasing costs	$ 453,833	$ 443,341
Less: accumulated amortization	(244,723)	(217,140)
Deferred costs, net	$ 209,110	$ 226,201

Mortgages and Other Loans Pay_3

Mortgages and Other Loans Payable (Details)	3 Months Ended				12 Months Ended
	Dec. 31, 2018USD ($)debt_instrument	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)debt_instrumentextension	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Apr. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Jul. 31, 2016USD ($)
Debt Instrument [Line Items]
Total fixed rate debt	$ 1,389,717,000				$ 1,389,717,000	$ 2,400,560,000
Total floating rate debt	598,442,000				598,442,000	465,431,000
Total fixed rate and floating rate debt	1,988,159,000				1,988,159,000	2,865,991,000
Mortgages reclassed to liabilities related to assets held for sale	0				0	0
Total mortgages and other loans payable	1,988,159,000				1,988,159,000	2,865,991,000
Deferred financing costs, net of amortization	(26,919,000)				(26,919,000)	(28,709,000)
Total mortgages and other loans payable	1,961,240,000				1,961,240,000	2,837,282,000
Loss on early extinguishment of debt	14,889,000	$ 2,194,000	$ 0	$ 0	17,083,000	0	$ 0
Collateral already posted, aggregate fair value	3,900,000,000				3,900,000,000	4,800,000,000
Revolving credit facility, net	492,196,000				492,196,000	30,336,000
Series J Preferred Units
Debt Instrument [Line Items]
Total fixed rate debt	0				0	4,000,000
Unsecured Debt
Debt Instrument [Line Items]
Total fixed rate debt	$ 0				$ 0	16,000,000
Uncommitted Master Repurchase Agreements
Debt Instrument [Line Items]
Debt instrument, number of instruments | debt_instrument	2				2
FHLB Facility
Debt Instrument [Line Items]
Total floating rate debt	$ 13,000,000				$ 13,000,000	0
FHLB Facility | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	0.27%				0.27%
2017 Master Repurchase Agreement
Debt Instrument [Line Items]
Total floating rate debt	$ 300,000,000				$ 300,000,000	90,809,000
Initial Term (in Years)					1 year
Number of extension options | extension					2
Period of extension option					1 year
Maximum facility capacity								$ 400,000,000	$ 300,000,000
Extension option exercised, term					1 year
Revolving credit facility, net	$ 299,600,000				$ 299,600,000
2017 Master Repurchase Agreement | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.34%				2.34%
FHLB Facility, December 2019
Debt Instrument [Line Items]
Total floating rate debt	$ 14,500,000				$ 14,500,000	0
FHLB Facility, December 2019 | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	0.18%				0.18%
2016 Master Repurchase Agreement
Debt Instrument [Line Items]
Initial Term (in Years)					2 years
Period of extension option					1 year
Maximum facility capacity										$ 300,000,000
Basis point fee (as a percent)					0.25%
Threshold amount for basis point fee to be applicable (less than)					$ 150,000,000
2016 Master Repurchase Agreement | Minimum | LIBOR
Debt Instrument [Line Items]
Credit facility, interest rate (as a percent)					2.25%
2016 Master Repurchase Agreement | Maximum | LIBOR
Debt Instrument [Line Items]
Credit facility, interest rate (as a percent)					4.00%
762 Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 771,000				$ 771,000	771,000
762 Madison Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.00%				5.00%
100 Church Street
Debt Instrument [Line Items]
Total fixed rate debt	$ 213,208,000				$ 213,208,000	217,273,000
100 Church Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.68%				4.68%
420 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 300,000,000				$ 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%				3.99%
400 East 58th Street
Debt Instrument [Line Items]
Total fixed rate debt	$ 39,931,000				$ 39,931,000	40,000,000
400 East 58th Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.00%				3.00%
Initial Term (in Years)					5 years
1080 Amsterdam
Debt Instrument [Line Items]
Secured debt, bearing fixed interest, mortgage amount	$ 35,500,000				$ 35,500,000
Secured debt, bearing fixed interest, subordinate loan amount	$ 900,000				$ 900,000
1080 Amsterdam | Weighted Average
Debt Instrument [Line Items]
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%				3.50%
1080 Amsterdam | Senior Subordinated Loans | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	7.00%				7.00%
Landmark Square
Debt Instrument [Line Items]
Total fixed rate debt	$ 100,000,000				$ 100,000,000	100,000,000
Landmark Square | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.90%				4.90%
485 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 450,000,000				$ 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%				4.25%
1080 Amsterdam Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 35,807,000				$ 35,807,000	36,363,000
1080 Amsterdam Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.58%				3.58%
315 West 33rd Street
Debt Instrument [Line Items]
Total fixed rate debt	$ 250,000,000				$ 250,000,000	250,000,000
315 West 33rd Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.17%				4.17%
919 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 0				$ 0	500,000,000
One Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt		$ 0				486,153,000
Loss on early extinguishment of debt					14,900,000
113 Greene Street
Debt Instrument [Line Items]
Total floating rate debt	$ 15,523,000				$ 15,523,000	0
113 Greene Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.00%				2.00%
185 Broadway
Debt Instrument [Line Items]
Total floating rate debt	$ 111,869,000				$ 111,869,000	58,000,000
185 Broadway | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.85%				2.85%
712 Madison Avenue
Debt Instrument [Line Items]
Total floating rate debt	$ 28,000,000				$ 28,000,000	0
712 Madison Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.50%				2.50%
115 Spring Street
Debt Instrument [Line Items]
Total floating rate debt	$ 65,550,000				$ 65,550,000	0
115 Spring Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	3.40%				3.40%
719 Seventh Avenue
Debt Instrument [Line Items]
Total floating rate debt	$ 50,000,000				$ 50,000,000	41,622,000
719 Seventh Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.20%				1.20%
220 East 42nd Street
Debt Instrument [Line Items]
Total floating rate debt	$ 0				$ 0	275,000,000
220 East 42nd Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)
Construction Loans | 185 Broadway
Debt Instrument [Line Items]
Initial Term (in Years)					3 years
Number of extension options | extension					2
Period of extension option					1 year
Maximum facility capacity	$ 225,000,000				$ 225,000,000
Ticonderoga
Debt Instrument [Line Items]
FHLB advances, amount of advances	$ 13,000,000				$ 13,000,000	$ 14,500,000
Ticonderoga | LIBOR
Debt Instrument [Line Items]
Credit facility, interest rate (as a percent)					0.00%	0.00%

Corporate Indebtedness - Additi

Corporate Indebtedness - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018USD ($)extension	Dec. 31, 2017USD ($)
Corporate Indebtedness
Outstanding under line of credit facility	$ 492,196,000	$ 30,336,000
Long-term debt	$ 1,961,240,000	2,837,282,000
Revolving credit facility
Corporate Indebtedness
Facility fee (as a percent)	0.20%
Outstanding under line of credit facility	$ 500,000,000
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		1,000,000,000
Line of Credit | Term loan
Corporate Indebtedness
Long-term debt	1,500,000,000	1,500,000,000
Line of Credit | 2012 Credit Facility
Corporate Indebtedness
Long-term debt	492,200,000	$ 30,300,000
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, 2018	Dec. 31, 2017
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 5,588,159,000
Accreted Balance		1,495,214,000	$ 1,395,939,000
Deferred financing costs, net		(26,919,000)	(28,709,000)
Senior Unsecured Bonds | 4.50% 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		1,500,000,000
Accreted Balance		1,503,759,000	1,404,605,000
Deferred financing costs, net		(8,545,000)	(8,666,000)
Senior Notes, Net of Deferred Finance Costs		1,495,214,000	1,395,939,000
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	249,953,000
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 | 0.98% Senior unsecured notes maturing August 2021
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 350,000,000
Accreted Balance		$ 350,000,000	0
Coupon Rate (as a percent)		0.98%
Initial Term (in Years)		3 years
Senior unsecured notes | 3.25% Senior unsecured notes maturing October 2022
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 500,000,000
Accreted Balance		$ 499,591,000	499,489,000
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		$ 304,168,000	305,163,000
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, 2018
Principal Repayments and Joint Venture Debt
2,019		$ 33,741,000
2,020		576,640,000
2,021		501,505,000
2,022		1,008,017,000
2,023		1,922,851,000
Thereafter		1,545,405,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		$ 5,588,159,000
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
2,019		$ 115,295,000
2,020		278,791,000
2,021		518,371,000
2,022		220,810,000
2,023		277,996,000
Thereafter		2,430,198,000
Repayments of principal		3,841,461,000
Joint venture | Trust Preferred Securities
Principal Repayments and Joint Venture Debt
2,019		0
2,020		0
2,021		0
2,022		0
2,023		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
2,019		6,241,000
2,020		11,117,000
2,021		11,636,000
2,022		9,429,000
2,023		7,301,000
Thereafter		9,290,000
Principal Repayments and Joint Venture Debt
2,019		27,500,000
2,020		315,523,000
2,021		139,869,000
2,022		198,588,000
2,023		115,550,000
Thereafter		1,136,115,000
Future Amortization of Debt		55,014,000
Repayments of principal		1,933,145,000
Joint venture | Revolving Credit Facility
Principal Repayments and Joint Venture Debt
2,019		0
2,020		0
2,021		0
2,022		0
2,023		500,000,000
Thereafter		0
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		500,000,000
Joint venture | Unsecured Term Loans
Principal Repayments and Joint Venture Debt
2,019		0
2,020		0
2,021		0
2,022		0
2,023		1,300,000,000
Thereafter		200,000,000
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
2,019		0
2,020		250,000,000
2,021		350,000,000
2,022		800,000,000
2,023		0
Thereafter		100,000,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		$ 1,500,000,000

Corporate Indebtedness - Schedu

Corporate Indebtedness - Schedule of Consolidated Interest Expense, Excluding Capitalized Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest expense
Interest expense before capitalized interest	$ 244,788	$ 284,649	$ 348,062
Interest capitalized	(34,162)	(26,020)	(24,067)
Interest income	(1,957)	(1,584)	(2,796)
Interest expense, net	$ 208,669	$ 257,045	$ 321,199

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Operating expenses, paid to related parties		$ 17,823	$ 21,400	$ 21,890
Amounts due from/to related parties
Due from joint ventures		18,655	15,025
Other		9,378	8,014
Related party receivables		28,033	23,039
Alliance Building Services
Related Party Transaction [Line Items]
Profit participation from related party		3,900	3,900	3,500
Operating expenses, paid to related parties		18,800	22,600	23,400
Entity with Stephen L Green ownership interest
Related Party Transaction [Line Items]
Property management fees from related party		$ 600	$ 500	700
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 | Holiday and Mathias
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 | 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 t_3

Noncontrolling Interests on the Company's Consolidated Financial Statements - Additional Information (Details)	1 Months Ended	12 Months Ended
	Jan. 31, 2012$ / sharesshares	Dec. 31, 2018USD ($)shares$ / shares	Dec. 31, 2017USD ($)unit$ / sharesshares	Dec. 31, 2016USD ($)shares	Mar. 31, 2016shares	Aug. 31, 2015shares	Jul. 31, 2015shares	Jun. 30, 2015shares	Feb. 28, 2015shares	Aug. 31, 2014shares
Organization
Basic weighted average common shares outstanding (in shares)		86,753,000	98,571,000	100,185,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $		$ 461,954,000
Distributions | $		(8,364,000)	$ (52,446,000)	$ (15,419,000)
Net income | $		12,216,000	3,995,000	10,136,000
Accumulated other comprehensive income allocation | $		(66,000)	(94,000)	$ 1,299,000
Balance at end of period | $		$ 387,805,000	$ 461,954,000
Number of company common stock issued on conversion of Series B preferred units		6.71348
Diluted weighted average common stock outstanding (shares)		91,530,000	103,403,000	104,881,000
SL Green Operating Partnership
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $		$ 461,954,000	$ 473,882,000
Distributions | $		(15,000,000)	(14,266,000)
Issuance of common units | $		23,655,000	25,723,000
Redemption of common units | $		(60,718,000)	(21,574,000)
Net income | $		12,216,000	3,995,000
Accumulated other comprehensive income allocation | $		(66,000)	(94,000)
Fair value adjustment | $		(34,236,000)	(5,712,000)
Balance at end of period | $		$ 387,805,000	$ 461,954,000	$ 473,882,000
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
Number of company common stock issue on redemption of operation partnership common units		1
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)		91,315,000	103,127,000	104,508,000
Noncontrolling interest in the operating partnership (as a percent)		4.70%	4.58%
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares)		4,130,579	4,452,979
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)		4,130,579
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Distributions | $		$ (8,364,000)	$ (52,446,000)	$ (15,419,000)
Accumulated other comprehensive income allocation | $		$ (66,000)	$ (94,000)	$ 1,299,000
Liquidation preference of preferred units (in dollars per share) | $ / shares		$ 25	$ 25
Stock-based compensation plans (shares)		215,000	276,000	373,000
Diluted weighted average common stock outstanding (shares)		91,530,000	103,403,000	104,881,000
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 t_4

Noncontrolling Interests on the Company's Consolidated Financial Statements - Preferred Unit Activity (Details) - SL Green Operating Partnership - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Rollforward Analysis of Preferred Unit Activity
Issuance of preferred units	$ 23,655	$ 25,723
Redemption of preferred units	(60,718)	(21,574)
Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period	301,735	302,010
Issuance of preferred units	0	0
Redemption of preferred units	(1,308)	(275)
Balance at end of period	$ 300,427	$ 301,735

Stockholders' Equity of the C_3

Stockholders' Equity of the Company - Additional Information (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
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 (in shares)	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 (in dollars per share)	$ 0.01	$ 0.01
Excess shares issued (shares)	0

Stockholders' Equity of the C_4

Stockholders' Equity of the Company - Stock Repurchase Program (Details)	3 Months Ended				12 Months Ended
	Dec. 31, 2018USD ($)$ / sharesshares	Sep. 30, 2018$ / sharesshares	Jun. 30, 2018USD ($)$ / sharesshares	Mar. 31, 2018$ / sharesshares	Dec. 31, 2018USD ($)increase	Dec. 31, 2017USD ($)$ / sharesshares	Aug. 31, 2016USD ($)
Class of Stock [Line Items]
Number of shares purchased (in shares) | shares	2,358,484	252,947	3,479,552	3,653,928		8,342,411
Maximum approximate dollar value of shares that may yet be purchased under the plan | $ / shares	$ 93.04	$ 99.75	$ 97.22	$ 97.07		$ 101.64
2016 Repurchase Program
Class of Stock [Line Items]
Stock repurchase program, authorized amount | $	$ 500,000,000		$ 500,000,000		$ 500,000,000	$ 500,000,000	$ 1,000,000,000
Number of increases to share repurchase program | increase					3
Stock repurchase program, authorized amount, total | $	$ 2,500,000,000				$ 2,500,000,000
Number of shares purchased (in shares) | shares	18,087,322	15,728,838	15,475,891	11,996,339		8,342,411

Stockholders' Equity of the C_5

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, 2018	Dec. 31, 2017	Mar. 31, 2015
Stockholders' Equity
Preferred stock, shares outstanding (in shares)		9,200,000	9,200,000
Perpetual Preferred stock, liquidation preference (in dollars per share)		$ 25	$ 25
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 (in shares)	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 C_6

Stockholders' Equity of the Company - Schedule of Common Stock Issued and Proceeds Received Dividend Reinvestments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 28, 2015
Stockholders' Equity
Common stock, shares authorized (in shares)	160,000,000	160,000,000
Dividend Reinvestment and Stock Purchase Plan (DRIP)
Stockholders' Equity
Common stock, shares authorized (in shares)				3,500,000
Issuance of common stock (in shares)	1,399	2,141	2,687
Dividend reinvestments/stock purchases under the DRSPP	$ 136	$ 223	$ 277

Stockholders' Equity of the C_7

Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic Earnings:
Income attributable to SL Green common stockholders	$ (61,219)	$ 88,209	$ 103,556	$ 101,766	$ 27,982	$ 38,869	$ 8,222	$ 11,351	$ 232,312	$ 86,424	$ 234,946
Less: distributed earnings allocated to participating securities									(552)	(471)	(634)
Net income attributable to SL Green common stockholders (numerator for basic earnings per share)									231,760	85,953	234,312
Effect of Dilutive Securities:
Add back: undistributed earnings allocated to participating securities									552	471	634
Add back: Effect of dilutive securities (redemption of units to common shares)									12,216	3,995	10,136
Diluted Earnings:
Income attributable to SL Green common stockholders (numerator for diluted earnings per share)									$ 244,528	$ 90,419	$ 245,082
Basic Shares:
Weighted average common shares outstanding (shares)									86,753,000	98,571,000	100,185,000
Effect of Dilutive Securities:
Redemption of units to common shares (shares)									4,562,000	4,556,000	4,323,000
Stock-based compensation plans (shares)									215,000	276,000	373,000
Diluted weighted average common stock outstanding (shares)									91,530,000	103,403,000	104,881,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,138,647	774,782	263,991

Partners' Capital of the Oper_3

Partners' Capital of the Operating Partnership - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018shares	Dec. 31, 2017unitshares	Dec. 31, 2016shares	Dec. 31, 2015shares
Common Stock
Stockholders' Equity
Units outstanding (units)	83,684,000	92,803,000	100,562,000	99,976,000
SL Green Operating Partnership
Stockholders' Equity
Noncontrolling interest in the operating partnership (as a percent)	4.70%	4.58%
Number of units of operating partnership owned by the noncontrolling interest unit holders (units)	4,130,579	4,452,979
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)	83,683,847

Partners' Capital of the Oper_4

Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator
Less: distributed earnings allocated to participating securities									$ (552)	$ (471)	$ (634)
Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic									231,760	85,953	234,312
Add back: undistributed earnings allocated to participating securities									$ (552)	$ (471)	$ (634)
Denominator
Weighted average common shares outstanding (shares)									86,753,000	98,571,000	100,185,000
Diluted weighted average common stock outstanding (shares)									91,530,000	103,403,000	104,881,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,138,647	774,782	263,991
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ (64,658)	$ 93,006	$ 109,142	$ 107,038	$ 29,270	$ 40,681	$ 8,641	$ 11,827	$ 244,528	$ 90,419	$ 245,082
Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic									243,976	89,948	244,448
Add back: undistributed earnings allocated to participating securities									$ 552	$ 471	$ 634
Denominator
Weighted average common shares outstanding (shares)									91,315,000	103,127,000	104,508,000
Stock-based compensation plans (shares)									215,000	276,000	373,000
Diluted weighted average common stock outstanding (shares)									91,530,000	103,403,000	104,881,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,138,647	774,782	263,991

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Details)	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2014shares	Dec. 31, 2018USD ($)unit / sharesfungible_unit$ / sharesshares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015shares
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				$ 6,300,000	$ 7,200,000	$ 6,000,000
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)				3 years 6 months 1 day	4 years 4 months 24 days	3 years 8 months 12 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 6 months 12 days
Remaining weighted average contractual life of the options exercisable (in years)				3 years 8 months 24 days
Total unrecognized compensation cost related to unvested stock awards				$ 2,600,000
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)				1 year 1 day
Weighted average fair value of options granted during the period				$ 84,068	$ 3,816,652	$ 8,363,036
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				$ 12,757,704	9,809,749	7,153,966
Total unrecognized compensation cost related to unvested stock awards				$ 22,700,000
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)				2 years 3 months 12 days
Fair value of restricted stock vested during the period				$ 9,800,000	9,400,000	7,600,000
Weighted average fair value of options granted during the period				$ 13,440,503	$ 9,905,986	$ 10,650,077
Awards granted (in shares) | shares				162,900	96,185	98,800
Awards outstanding (in shares) | shares				3,452,016	3,298,216	3,202,031	3,137,881
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 3 months 24 days
Weighted average fair value of options granted during the period				$ 22,000,000	$ 20,500,000
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost related to unvested stock awards				2,900,000
Share-based Compensation				$ 24,400,000	26,100,000	$ 26,500,000
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for issuance (shares) | 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				116,368
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				6,700,000
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				$ 5,400,000	7,800,000	8,900,000
2014 Outperformance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense				0	$ 13,600,000	$ 8,400,000
Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options				27,900,000
Maximum award to be earned, if performance reaches maximum threshold, first performance period			0.333
Maximum award to be earned, if performance reaches maximum threshold, first performance period			0.667
Award period (in years)			3 years
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%
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%
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				13,638
Shares issued (in shares) | shares				9,459
Awards outstanding (in shares) | shares				113,492

Share-based Compensation - Acti

Share-based Compensation - Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares held in employee trust (in shares)	116,368
Stock options
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Dividend yield (as a percent)	2.85%	2.51%	2.37%
Expected life of option (in years)	3 years 6 months 1 day	4 years 4 months 24 days	3 years 8 months 12 days
Risk-free interest rate (as a percent)	2.48%	1.73%	1.57%
Expected stock price volatility (as a percent)	22.00%	28.10%	26.76%
Options Outstanding
Balance at beginning of year (in shares)	1,548,719	1,737,213	1,595,007
Granted (in shares)	6,000	174,000	445,100
Exercised (in shares)	(316,302)	(292,193)	(192,875)
Lapsed or cancelled (in shares)	(101,400)	(70,301)	(110,019)
Balance at end of period (in shares)	1,137,017	1,548,719	1,737,213
Options exercisable at end of period (in shares)	783,035	800,902	748,617
Weighted average fair value of options granted during the period	$ 84,068	$ 3,816,652	$ 8,363,036
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 101.48	$ 98.44	$ 95.52
Granted (in dollars per share)	97.91	105.66	105.86
Exercised (in dollars per share)	90.22	81.07	76.90
Lapsed or cancelled (in dollars per share)	113.22	121.68	123.86
Balance at end of period (in dollars per share)	135.54	101.48	98.44
Options exercisable at end of period (in dollars per share)	$ 101.28	$ 94.33	$ 87.72
Restricted Stock Awards
Options Outstanding
Weighted average fair value of options granted during the period	$ 13,440,503	$ 9,905,986	$ 10,650,077
Summary of restricted stock
Balance at beginning of year (in shares)	3,298,216	3,202,031	3,137,881
Granted (in shares)	162,900	96,185	98,800
Cancelled (in shares)	(9,100)	0	(34,650)
Balance at end of period (in shares)	3,452,016	3,298,216	3,202,031
Vested during the period (in shares)	92,114	95,736	83,822
Compensation expense recorded	$ 12,757,704	$ 9,809,749	$ 7,153,966

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	$ 6,589,454	$ 7,750,911	$ 7,719,317
Other comprehensive (loss) income before reclassifications	(2,304)	(2,733)	18,211
Amounts reclassified from accumulated other comprehensive income	(1,192)	(800)	12,675
Ending Balance	5,947,855	6,589,454	7,750,911
Deferred net losses from terminated hedges	1,300	3,200
Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	12,542	12,596	(10,160)
Other comprehensive (loss) income before reclassifications	(2,252)	(1,618)	13,534
Amounts reclassified from accumulated other comprehensive income	(574)	1,564	9,222
Ending Balance	9,716	12,542	12,596
Net unrealized gain on marketable securities
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	1,042	5,520	2,003
Other comprehensive (loss) income before reclassifications	51	(1,348)	3,517
Amounts reclassified from accumulated other comprehensive income	0	(3,130)	0
Ending Balance	1,093	1,042	5,520
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	18,604	22,137	(8,749)
Ending Balance	15,108	18,604	22,137
Joint venture | Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	5,020	4,021	(592)
Other comprehensive (loss) income before reclassifications	(103)	233	1,160
Amounts reclassified from accumulated other comprehensive income	(618)	766	3,453
Ending Balance	$ 4,299	$ 5,020	$ 4,021

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				12 Months Ended
	May 31, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value of Financial Instruments
Marketable securities		$ 28,638				$ 28,638	$ 28,579
Interest rate cap and swap agreements (included in other assets)		18,676				18,676	16,692
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		7,663				7,663
Asset impairment loss						221,900
Purchase price and other fair value adjustment		0	$ (3,057)	$ 11,149	$ 49,293	57,385	0	$ 0
Debt and preferred equity investments		2,099,393				2,099,393	2,114,041
Carrying Value
Fair Value of Financial Instruments
Fixed rate debt		3,543,476				3,543,476	4,305,165
Variable rate debt		2,048,442				2,048,442	1,605,431
Total		5,591,918				5,591,918	5,910,596
Fair Value
Fair Value of Financial Instruments
Marketable securities		28,638				28,638	28,579
Total		5,288,093				5,288,093	6,034,090
Estimated fair value of debt and preferred equity investments, low end of range		2,100,000				2,100,000	2,100,000
Estimated fair value of debt and preferred equity investments, high end of range		2,300,000				2,300,000	2,300,000
Level 1
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in other assets)		0				0	0
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		0				0
Level 2
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in other assets)		18,676				18,676	16,692
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		7,663				7,663
Level 3
Fair Value of Financial Instruments
Marketable securities		0				0	0
Interest rate cap and swap agreements (included in other assets)		0				0	0
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		0				0
Level 3 | Carrying Value
Fair Value of Financial Instruments
Debt and preferred equity investments							2,114,041
Level 3 | Fair Value
Fair Value of Financial Instruments
Fixed rate debt		3,230,127				3,230,127	4,421,866
Variable rate debt		2,057,966				2,057,966	1,612,224
Equity marketable securities | Level 1
Fair Value of Financial Instruments
Marketable securities		0				0	0
Mortgage-backed securities
Fair Value of Financial Instruments
Marketable securities		28,638				28,638	28,579
Mortgage-backed securities | Level 2
Fair Value of Financial Instruments
Marketable securities		28,638				28,638	28,579
Total fixed rate | Mortgage and Jr Mortgage Loan with an Initial Maturity Date of April 2017
Fair Value of Financial Instruments
Notes receivable	$ 250,500
Interest receivable	7,700
2 Herald Square
Fair Value of Financial Instruments
Purchase price fair value adjustment	$ 8,100
Joint venture
Fair Value of Financial Instruments
Debt and preferred equity investments		$ 44,357				44,357	$ 202,539
Joint venture | 919 Third Avenue | 919 Third Avenue
Fair Value of Financial Instruments
Purchase price and other fair value adjustment						$ 49,300

Financial Instruments_ Deriva_3

Financial Instruments: Derivatives and Hedging (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financial Instruments: Derivatives and Hedging
Fair Value	$ 18,676	$ 16,692
Gain (loss) from changes in fair value	(200)	(500)	$ 500
Fair value of derivatives in a net liability position	7,700
Aggregate termination value	7,700
Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion)	(4,072)	(2,482)	16,628
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	1,335	2,856	11,502
Amount of (Loss) Gain Recognized into Income (Ineffective Portion)	(930)	60	757
Interest Rate Swap Expiring in July 2023
Financial Instruments: Derivatives and Hedging
Notional Value	$ 200,000
Strike Rate	1.131%
Fair Value	$ 11,148
Interest Rate Swap Expiring in July 2023, 2
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000
Strike Rate	1.161%
Fair Value	$ 5,447
Interest Rate Cap Expiring September 2019
Financial Instruments: Derivatives and Hedging
Notional Value	$ 137,500
Strike Rate	4.00%
Fair Value	$ 0
Interest Rate Swap Expiring November 2020
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000
Strike Rate	1.928%
Fair Value	$ 1,045
Interest Rate Swap Expiring November 2020, 2
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000
Strike Rate	1.934%
Fair Value	$ 1,035
Interest Rate Swap Expiring January 2024
Financial Instruments: Derivatives and Hedging
Notional Value	$ 150,000
Strike Rate	2.6955%
Fair Value	$ (1,858)
Interest Rate Swap Expiring January 2026
Financial Instruments: Derivatives and Hedging
Notional Value	$ 150,000
Strike Rate	2.721%
Fair Value	$ (2,450)
Interest Rate Swap Expiring January 2026, 2
Financial Instruments: Derivatives and Hedging
Notional Value	$ 200,000
Strike Rate	2.74%
Fair Value	$ (3,354)
Interest Rate Swap
Financial Instruments: Derivatives and Hedging
Fair Value	11,013
Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion)	(2,284)	(2,282)	14,616
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	609	1,821	9,521
Amount of (Loss) Gain Recognized into Income (Ineffective Portion)	(559)	5	(28)
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	2,500
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	600
Joint venture
Financial Instruments: Derivatives and Hedging
Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion)	(1,788)	(200)	2,012
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	726	1,035	1,981
Amount of (Loss) Gain Recognized into Income (Ineffective Portion)	$ (371)	$ 55	$ 785

Rental Income (Details)

Rental Income (Details) $ in Thousands	Dec. 31, 2018USD ($)
Consolidated properties
Operating Leased Assets [Line Items]
2,019	$ 830,336
2,020	765,610
2,021	625,956
2,022	562,250
2,023	500,499
Thereafter	3,272,014
Total minimum lease payments	6,556,665
Unconsolidated properties
Operating Leased Assets [Line Items]
2,019	348,060
2,020	375,228
2,021	380,886
2,022	348,222
2,023	333,501
Thereafter	2,098,995
Total minimum lease payments	$ 3,884,892

Benefit Plans (Details)

Benefit Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Multiemployer Plans [Line Items]
Plan contributions	$ 13,433,000		$ 16,745,000		$ 17,092,000
401 (K) Plan
Employee contribution limit per calendar year	15.00%
Employer matching contribution, percent of match	100.00%		50.00%		50.00%
Percentage of eligible compensation matched by employer	4.00%		6.00%		6.00%
Matching contribution	$ 1,075,267		$ 1,011,830		$ 906,875
Health Plan
Multiemployer Plans [Line Items]
Plan contributions	$ 9,310,000		11,426,000		11,530,000
Multiemployer plan, contributions by employer		$ 1,400,000,000		$ 1,300,000,000		$ 1,200,000,000
Percentage of contributions required for multiple collective-bargaining arrangements	5.00%
Other plans
Multiemployer Plans [Line Items]
Plan contributions	$ 1,106,000		1,463,000		1,583,000
Pension Plan
Multiemployer Plans [Line Items]
Multiemployer plans, surcharge	No
Plan contributions	$ 3,017,000	$ 272,300,000	$ 3,856,000	$ 257,800,000	$ 3,979,000	$ 249,500,000
Multiemployer plans, contributions by employer, percent	5.00%

Commitments and Contingencies_2

Commitments and Contingencies (Details)	12 Months Ended
	Dec. 31, 2018USD ($)option	Dec. 31, 2017USD ($)
Other Commitments [Line Items]
Employment agreements with certain executives, minimum cash-based compensation for next fiscal year	$ 3,300,000
Capital lease obligations	$ 43,616,000	$ 42,843,000
Initial term of non cancellable operating leases, minimum (in years)	1 year
Capital lease
2,019	$ 2,411,000
2,020	2,620,000
2,021	2,794,000
2,022	2,794,000
2,023	2,794,000
Thereafter	817,100,000
Total minimum lease payments	830,513,000
Amount representing interest	(786,897,000)
Capital lease obligations	43,616,000
Non-cancellable operating leases (1)
2,019	31,066,000
2,020	31,436,000
2,021	31,628,000
2,022	29,472,000
2,023	27,166,000
Thereafter	676,090,000
Total minimum lease payments	826,858,000
Minimum sublease rentals to be received in the future	$ 1,700,000,000
30 East 40th Street
Other Commitments [Line Items]
Land as percentage of fair market value of property under lease	63.60%
Capital lease obligations	$ 20,000,000
Non-cancellable operating leases (1)
Total minimum lease payments	$ 76,000,000
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	$ 10,900,000
Annual ground lease payments, year seven to year sixteen	11,200,000
Annual ground lease payments due thereafter	$ 12,300,000
Number of renewal options available (extension option) | option	2
Term of first renewal option (in years)	30 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 (1)
Total minimum lease payments	$ 41,600,000
711 Third Avenue
Other Commitments [Line Items]
Number of renewal options available (extension option) | option	5
Term of first renewal option (in years)	10 years
Percentage of the fee not owned by the entity (percent)	50.00%
711 Third Avenue | Through July 2016
Other Commitments [Line Items]
Required annual ground lease payments	$ 5,250,000
711 Third Avenue | After July 2016
Other Commitments [Line Items]
Required annual ground lease payments	5,500,000
711 Third Avenue | After July 2021
Other Commitments [Line Items]
Required annual ground lease payments	$ 5,500,000
Annual ground lease payments, percent of fair value of land	7.75%
461 Fifth Avenue
Other Commitments [Line Items]
Number of renewal options available (extension option) | option	2
Term of first renewal option (in years)	21 years
Required annual ground lease payments	$ 2,100,000
Term of third renewal option	15 years
625 Madison Avenue
Other Commitments [Line Items]
Number of renewal options available (extension option) | option	2
Term of first renewal option (in years)	32 years
Required annual ground lease payments	$ 4,600,000
1185 Avenue of the Americas
Other Commitments [Line Items]
Required annual ground lease payments	6,900,000
1055 Washington Boulevard
Other Commitments [Line Items]
Required annual ground lease payments	600,000
Belmont
Other Commitments [Line Items]
Loss reserves	4,000,000	$ 5,500,000
Ticonderoga
Other Commitments [Line Items]
Loss reserves	$ 0

Segment Information - Additiona

Segment Information - Additional Information (Details) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Segment information
Number of reportable segments (segment) | segment										2
Total revenues		$ 317,036	$ 307,545	$ 301,116	$ 301,695	$ 361,342	$ 374,600	$ 398,150	$ 377,381	$ 1,227,392	$ 1,511,473	$ 1,863,981
Net Income										270,856	101,069	278,911
Total assets	[1]	12,751,358				13,982,904				12,751,358	13,982,904
Marketing, general and administrative										92,631	100,498	99,759
Operating Segments | Real Estate Segment
Segment information
Total revenues										1,025,900	1,317,602	1,650,973
Net Income										129,253	(69,294)	74,655
Total assets		10,481,594				11,598,438				10,481,594	11,598,438
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues										201,492	193,871	213,008
Net Income										141,603	170,363	$ 204,256
Total assets		$ 2,269,764				$ 2,384,466				$ 2,269,764	$ 2,384,466
[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: $110.0 million and $398.0 million of land, $0.3 billion and $1.4 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, $42.2 million and $330.9 million of accumulated depreciation, $721.3 million and $221.0 million of other assets included in other line items, $140.8 million and $628.9 million of real estate debt, net, $0.4 million and $2.5 million of accrued interest payable, $43.6 million and $42.8 million of capital lease obligations, and $18.4 million and $56.8 million of other liabilities included in other line items as of December 31, 2018 and December 31, 2017, respectively.

Quarterly Financial Data of t_5

Quarterly Financial Data of the Company (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 317,036	$ 307,545	$ 301,116	$ 301,695	$ 361,342	$ 374,600	$ 398,150	$ 377,381	$ 1,227,392	$ 1,511,473	$ 1,863,981
Total expenses	(267,678)	(265,553)	(258,303)	(258,282)	(314,108)	(333,913)	(365,749)	(332,675)	(1,049,816)	(1,346,445)	(1,868,599)
Equity in net income from unconsolidated joint ventures	(2,398)	971	4,702	4,036	7,788	4,078	3,412	6,614	7,311	21,892	11,874
Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate	167,445	70,937	72,025	(6,440)	0	1,030	13,089	2,047	303,967	16,166	44,009
Gain on sale of real estate, net	(36,984)	(2,504)	(14,790)	23,521	76,497	0	(3,823)	567	(30,757)	73,241	238,116
Purchase price and other fair value adjustment	0	(3,057)	11,149	49,293					57,385	0	0
Depreciable real estate reserves and impairment	(220,852)	(6,691)	0	0	(93,184)	0	(29,064)	(56,272)	(227,543)	(178,520)	(10,387)
Change in unrealized gain (loss) on marketable securities					0	0	0	3,262
Loss on early extinguishment of debt	(14,889)	(2,194)	0	0					(17,083)	0	0
Noncontrolling interests and preferred unit distributions	838	(7,507)	(8,606)	(8,319)	(6,616)	(3,188)	(4,056)	14,165
Net income (loss) attributable to SL Green/SLGOP	(57,482)	91,947	107,293	105,504	31,719	42,607	11,959	15,089	247,262	101,374	249,896
Perpetual preferred stock dividends	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(14,950)	(14,950)	(14,950)
Net income attributable to SL Green common stockholders	$ (61,219)	$ 88,209	$ 103,556	$ 101,766	$ 27,982	$ 38,869	$ 8,222	$ 11,351	$ 232,312	$ 86,424	$ 234,946
Net (loss) income attributable to common stockholders per common share - basic (usd per share)	$ (0.73)	$ 1.03	$ 1.19	$ 1.12	$ 0.29	$ 0.40	$ 0.08	$ 0.11
Net (loss) income attributable to common stockholders per common share - diluted (usd per share)	$ (0.73)	$ 1.03	$ 1.19	$ 1.12	$ 0.29	$ 0.40	$ 0.08	$ 0.11

Quarterly Financial Data of t_6

Quarterly Financial Data of the Operating Partnership (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]
Total revenues	$ 317,036	$ 307,545	$ 301,116	$ 301,695	$ 361,342	$ 374,600	$ 398,150	$ 377,381	$ 1,227,392	$ 1,511,473	$ 1,863,981
Total expenses	(267,678)	(265,553)	(258,303)	(258,282)	(314,108)	(333,913)	(365,749)	(332,675)	(1,049,816)	(1,346,445)	(1,868,599)
Equity in net income from unconsolidated joint ventures	(2,398)	971	4,702	4,036	7,788	4,078	3,412	6,614	7,311	21,892	11,874
Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate	167,445	70,937	72,025	(6,440)	0	1,030	13,089	2,047	303,967	16,166	44,009
(Loss) gain on sale of real estate, net	(36,984)	(2,504)	(14,790)	23,521	76,497	0	(3,823)	567	(30,757)	73,241	238,116
Purchase price and other fair value adjustment	0	(3,057)	11,149	49,293					57,385	0	0
Depreciable real estate reserves and impairment	(220,852)	(6,691)	0	0	(93,184)	0	(29,064)	(56,272)	(227,543)	(178,520)	(10,387)
Gain (loss) on sale of investment in marketable securities									0	3,262	(83)
Loss on early extinguishment of debt	(14,889)	(2,194)	0	0					(17,083)	0	0
Noncontrolling interests and preferred unit distributions	838	(7,507)	(8,606)	(8,319)	(6,616)	(3,188)	(4,056)	14,165
Net income (loss) attributable to SL Green/SLGOP	(57,482)	91,947	107,293	105,504	31,719	42,607	11,959	15,089	247,262	101,374	249,896
SL Green Operating Partnership
Condensed Income Statements, Captions [Line Items]
Total revenues	317,036	307,545	301,116	301,695	361,342	374,600	398,150	377,381	1,227,392	1,511,473	1,863,981
Total expenses	(267,678)	(265,553)	(258,303)	(258,282)	(314,108)	(333,913)	(365,749)	(332,675)	(1,049,816)	(1,346,445)	(1,868,599)
Equity in net income from unconsolidated joint ventures	(2,398)	971	4,702	4,036	7,788	4,078	3,412	6,614	7,311	21,892	11,874
Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate	167,445	70,937	72,025	(6,440)	0	1,030	13,089	2,047	303,967	16,166	44,009
(Loss) gain on sale of real estate, net	(36,984)	(2,504)	(14,790)	23,521	76,497	0	(3,823)	567	(30,757)	73,241	238,116
Purchase price and other fair value adjustment	0	(3,057)	11,149	49,293					57,385	0	0
Depreciable real estate reserves and impairment	(220,852)	(6,691)	0	0	(93,184)	0	(29,064)	(56,272)	(227,543)	(178,520)	(10,387)
Gain (loss) on sale of investment in marketable securities					0	0	0	3,262	0	3,262	(83)
Loss on early extinguishment of debt	(14,889)	(2,194)	0	0					(17,083)	0	0
Noncontrolling interests and preferred unit distributions	(2,601)	(2,710)	(3,020)	(3,047)	(5,328)	(1,376)	(3,637)	14,641	(14,950)	(14,950)	(14,950)
Net income (loss) attributable to SL Green/SLGOP	(60,921)	96,744	112,879	110,776	33,007	44,419	12,378	15,565	259,478	105,369	260,032
Perpetual preferred stock dividends	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(14,950)	(14,950)	(14,950)
Net income attributable to SLGOP common unitholders	$ (64,658)	$ 93,006	$ 109,142	$ 107,038	$ 29,270	$ 40,681	$ 8,641	$ 11,827	$ 244,528	$ 90,419	$ 245,082
Net income attributable to common unitholders per common share—basic (in dollars per share)	$ (0.73)	$ 1.03	$ 1.19	$ 1.12	$ 0.29	$ 0.40	$ 0.08	$ 0.11	$ 2.67	$ 0.87	$ 2.34
Net income attributable to common unitholders per common share—diluted (in dollars per share)	$ (0.73)	$ 1.03	$ 1.19	$ 1.12	$ 0.29	$ 0.40	$ 0.08	$ 0.11	$ 2.67	$ 0.87	$ 2.34

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Tenant and other receivables—allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 18,637	$ 16,592	$ 17,618
Additions Charged Against Operations	3,726	6,106	10,630
Uncollectible Accounts Written-off/Recovery (1)	(6,661)	(4,061)	(11,656)
Balance at End of Year	15,702	18,637	16,592
Deferred rent receivable—allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	17,207	25,203	21,730
Additions Charged Against Operations	491	2,321	13,620
Uncollectible Accounts Written-off/Recovery (1)	(2,241)	(10,317)	(10,147)
Balance at End of Year	$ 15,457	$ 17,207	$ 25,203

Schedule III - Real Estate an_2

Schedule III - Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 1,660,659
Initial Cost
Land	1,776,213
Building & Improvements	5,370,786
Cost Capitalized Subsequent To Acquisition
Land	(1,314)
Building & Improvements	1,368,250
Gross Amount at Which Carried at Close of Period
Land	1,774,899
Building & Improvements	6,739,036
Total	8,513,935	$ 10,206,122	$ 12,743,332	$ 16,681,602
Accumulated Depreciation	2,099,137	$ 2,300,116	$ 2,264,694	$ 2,060,706
420 Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	225,667
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	333,499
Total	333,499
Accumulated Depreciation	133,978
711 Third Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	73,270
Gross Amount at Which Carried at Close of Period
Land	19,844
Building & Improvements	115,769
Total	135,613
Accumulated Depreciation	45,066
555 W. 57th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	62,242
Gross Amount at Which Carried at Close of Period
Land	18,846
Building & Improvements	140,946
Total	159,792
Accumulated Depreciation	69,817
220 East 42nd Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	50,373
Building & Improvements	203,727
Cost Capitalized Subsequent To Acquisition
Land	635
Building & Improvements	161,705
Gross Amount at Which Carried at Close of Period
Land	51,008
Building & Improvements	365,432
Total	416,440
Accumulated Depreciation	108,450
461 Fifth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	25,581
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	88,276
Total	88,276
Accumulated Depreciation	29,680
750 Third Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	45,551
Gross Amount at Which Carried at Close of Period
Land	51,093
Building & Improvements	251,523
Total	302,616
Accumulated Depreciation	101,854
625 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	44,646
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	291,319
Total	291,319
Accumulated Depreciation	118,380
485 Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	125,806
Gross Amount at Which Carried at Close of Period
Land	78,282
Building & Improvements	452,631
Total	530,913
Accumulated Depreciation	183,003
609 Fifth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	49,527
Gross Amount at Which Carried at Close of Period
Land	36,677
Building & Improvements	195,481
Total	232,158
Accumulated Depreciation	43,777
810 Seventh Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	74,433
Gross Amount at Which Carried at Close of Period
Land	114,077
Building & Improvements	550,819
Total	664,896
Accumulated Depreciation	176,354
1185 Avenue of the Americas
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	62,893
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	791,106
Total	791,106
Accumulated Depreciation	265,896
1350 Avenue of the Americas
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	50,773
Gross Amount at Which Carried at Close of Period
Land	90,941
Building & Improvements	431,517
Total	522,458
Accumulated Depreciation	136,853
100 Summit Lake Drive
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	10,526
Building & Improvements	43,109
Cost Capitalized Subsequent To Acquisition
Land	(3,337)
Building & Improvements	(94)
Gross Amount at Which Carried at Close of Period
Land	7,189
Building & Improvements	43,015
Total	50,204
Accumulated Depreciation	18,936
200 Summit Lake Drive
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	11,183
Building & Improvements	47,906
Cost Capitalized Subsequent To Acquisition
Land	(5,321)
Building & Improvements	(9,102)
Gross Amount at Which Carried at Close of Period
Land	5,862
Building & Improvements	38,804
Total	44,666
Accumulated Depreciation	21,203
500 Summit Lake Drive
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	9,777
Building & Improvements	39,048
Cost Capitalized Subsequent To Acquisition
Land	(3,601)
Building & Improvements	(7,875)
Gross Amount at Which Carried at Close of Period
Land	6,176
Building & Improvements	31,173
Total	37,349
Accumulated Depreciation	14,523
360 Hamilton Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	29,497
Building & Improvements	118,250
Cost Capitalized Subsequent To Acquisition
Land	(2,625)
Building & Improvements	8,005
Gross Amount at Which Carried at Close of Period
Land	26,872
Building & Improvements	126,255
Total	153,127
Accumulated Depreciation	43,901
1-6 Landmark Square
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	(23,095)
Building & Improvements	(33,824)
Gross Amount at Which Carried at Close of Period
Land	27,852
Building & Improvements	161,343
Total	189,195
Accumulated Depreciation	79,012
7 Landmark Square
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	669
Gross Amount at Which Carried at Close of Period
Land	1,721
Building & Improvements	8,417
Total	10,138
Accumulated Depreciation	1,539
1010 Washington Boulevard
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	7,747
Building & Improvements	30,423
Cost Capitalized Subsequent To Acquisition
Land	(1,259)
Building & Improvements	2,928
Gross Amount at Which Carried at Close of Period
Land	6,488
Building & Improvements	33,351
Total	39,839
Accumulated Depreciation	12,489
1055 Washington Boulevard
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	13,516
Building & Improvements	53,228
Cost Capitalized Subsequent To Acquisition
Land	(5,130)
Building & Improvements	(9,986)
Gross Amount at Which Carried at Close of Period
Land	8,386
Building & Improvements	43,242
Total	51,628
Accumulated Depreciation	20,382
One Madison Ave
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	172,641
Building & Improvements	654,394
Cost Capitalized Subsequent To Acquisition
Land	905
Building & Improvements	18,411
Gross Amount at Which Carried at Close of Period
Land	173,546
Building & Improvements	672,805
Total	846,351
Accumulated Depreciation	193,033
100 Church Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	213,208
Initial Cost
Land	32,494
Building & Improvements	79,996
Cost Capitalized Subsequent To Acquisition
Land	2,500
Building & Improvements	103,936
Gross Amount at Which Carried at Close of Period
Land	34,994
Building & Improvements	183,932
Total	218,926
Accumulated Depreciation	53,269
125 Park Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	80,884
Gross Amount at Which Carried at Close of Period
Land	120,900
Building & Improvements	270,598
Total	391,498
Accumulated Depreciation	77,542
Williamsburg
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	2,127
110 East 42nd Street
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	31,942
Gross Amount at Which Carried at Close of Period
Land	36,196
Building & Improvements	78,353
Total	114,549
Accumulated Depreciation	17,400
400 East 58th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	39,931
Initial Cost
Land	17,549
Building & Improvements	30,916
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	7,833
Gross Amount at Which Carried at Close of Period
Land	17,549
Building & Improvements	38,749
Total	56,298
Accumulated Depreciation	$ 6,119
Interest in property (as a percent)	90.00%
752 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	1,183
Gross Amount at Which Carried at Close of Period
Land	284,286
Building & Improvements	8,314
Total	292,600
Accumulated Depreciation	1,380
762 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	109
Gross Amount at Which Carried at Close of Period
Land	6,153
Building & Improvements	10,570
Total	16,723
Accumulated Depreciation	$ 1,884
Interest in property (as a percent)	90.00%
19-21 East 65th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	1,100
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	8,489
Total	8,489
Accumulated Depreciation	$ 1,228
Interest in property (as a percent)	90.00%
304 Park Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	15,024
Gross Amount at Which Carried at Close of Period
Land	54,489
Building & Improvements	90,643
Total	145,132
Accumulated Depreciation	19,315
635 Sixth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	51,103
Gross Amount at Which Carried at Close of Period
Land	24,343
Building & Improvements	88,261
Total	112,604
Accumulated Depreciation	10,931
641 Sixth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	9,760
Gross Amount at Which Carried at Close of Period
Land	45,976
Building & Improvements	77,076
Total	123,052
Accumulated Depreciation	15,891
1080 Amsterdam
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	35,807
Initial Cost
Land	0
Building & Improvements	27,445
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	20,503
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	47,948
Total	47,948
Accumulated Depreciation	$ 5,441
Interest in property (as a percent)	92.50%
315 West 33rd Street
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	15,133
Gross Amount at Which Carried at Close of Period
Land	195,834
Building & Improvements	179,562
Total	375,396
Accumulated Depreciation	25,397
562 Fifth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	4,458
719 Seventh Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	50,000
Initial Cost
Land	41,850
Building & Improvements	0
Cost Capitalized Subsequent To Acquisition
Land	(670)
Building & Improvements	46,232
Gross Amount at Which Carried at Close of Period
Land	41,180
Building & Improvements	46,232
Total	87,412
Accumulated Depreciation	$ 3,025
Interest in property (as a percent)	75.00%
115 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 65,550
Initial Cost
Land	11,078
Building & Improvements	44,799
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	1,850
Gross Amount at Which Carried at Close of Period
Land	11,078
Building & Improvements	46,649
Total	57,727
Accumulated Depreciation	5,248
1640 Flatbush Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	503
Gross Amount at Which Carried at Close of Period
Land	6,226
Building & Improvements	1,004
Total	7,230
Accumulated Depreciation	50
110 Greene Street
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	12,923
Gross Amount at Which Carried at Close of Period
Land	45,120
Building & Improvements	228,393
Total	273,513
Accumulated Depreciation	$ 23,683
Interest in property (as a percent)	90.00%
5- 7 Dey Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 111,869
Initial Cost
Land	13,400
Building & Improvements	34,175
Cost Capitalized Subsequent To Acquisition
Land	32,022
Building & Improvements	(6,310)
Gross Amount at Which Carried at Close of Period
Land	45,422
Building & Improvements	27,865
Total	73,287
Accumulated Depreciation	419
30 East 40th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in 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	6,654
Gross Amount at Which Carried at Close of Period
Land	4,652
Building & Improvements	26,654
Total	31,306
Accumulated Depreciation	$ 2,017
Interest in property (as a percent)	60.00%
113 Greene Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 15,523
Initial Cost
Land	3,446
Building & Improvements	27,542
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	0
Gross Amount at Which Carried at Close of Period
Land	3,446
Building & Improvements	27,542
Total	30,988
Accumulated Depreciation	119
712 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	28,000
Initial Cost
Land	7,207
Building & Improvements	47,397
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	0
Gross Amount at Which Carried at Close of Period
Land	7,207
Building & Improvements	47,397
Total	54,604
Accumulated Depreciation	0
Other
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	1,738
Building & Improvements	16,225
Cost Capitalized Subsequent To Acquisition
Land	(2)
Building & Improvements	(1)
Gross Amount at Which Carried at Close of Period
Land	1,736
Building & Improvements	16,224
Total	17,960
Accumulated Depreciation	$ 4,068

Schedule III - Real Estate an_3

Schedule III - Real Estate and Accumulated Depreciation (Activity in Real Estate and Accumulated Depreciation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in real estate
Balance at beginning of year	$ 10,206,122	$ 12,743,332	$ 16,681,602
Property acquisitions	52,939	13,323	29,230
Improvements	267,726	342,014	426,060
Retirements/disposals/deconsolidation	(2,012,852)	(2,892,547)	(4,393,560)
Balance at end of year	8,513,935	10,206,122	12,743,332
Aggregate cost of land, buildings and improvements before depreciation	9,900,000
Changes in accumulated depreciation
Balance at beginning of year	2,300,116	2,264,694	2,060,706
Depreciation for year	245,033	347,015	353,502
Retirements/disposals/deconsolidation	(446,012)	(311,593)	(149,514)
Balance at end of year	$ 2,099,137	$ 2,300,116	$ 2,264,694

Uncategorized Items - slg-20181

Label	Element	Value
Accounting Standards Update 2014-09 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 570,524,000