SL Green Realty (SLG) 10-Q 8 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Aug. 07, 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-Q
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		86,566,698
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-Q
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		1,468,438

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Commercial real estate properties, at cost:
Land and land interests		$ 1,893,047	$ 2,357,051
Building and improvements		5,225,431	6,351,012
Building leasehold and improvements		1,423,994	1,450,614
Properties under capital lease		47,445	47,445
Total commercial real estate properties, at cost		8,589,917	10,206,122
Less: accumulated depreciation		(1,994,696)	(2,300,116)
Total commercial real estate properties, net		6,595,221	7,906,006
Assets held for sale		593,995	338,354
Cash and cash equivalents		287,240	127,888
Restricted cash		92,740	122,138
Investments in marketable securities		28,570	28,579
Tenant and other receivables, net of allowance of $16,558 and $18,637 in 2018 and 2017, respectively		47,482	57,644
Related party receivables		27,854	23,039
Deferred rents receivable, net of allowance of $15,776 and $17,207 in 2018 and 2017, respectively		322,656	365,337
Debt and preferred equity investments, net of discounts and deferred origination fees of $23,216 and $25,507 in 2018 and 2017, respectively		2,168,515	2,114,041
Investments in unconsolidated joint ventures		3,059,985	2,362,989
Deferred costs, net		198,941	226,201
Other assets		290,729	310,688
Total assets	[1]	13,713,928	13,982,904
Liabilities
Mortgages and other loans payable, net		2,517,097	2,837,282
Revolving credit facility, net		351,272	30,336
Unsecured term loan, net		1,492,320	1,491,575
Unsecured notes, net		1,396,722	1,395,939
Accrued interest payable		26,104	38,142
Other liabilities		108,151	188,005
Accounts payable and accrued expenses		140,739	137,142
Deferred revenue		95,756	208,119
Capital lease obligations		43,221	42,843
Deferred land leases payable		3,567	3,239
Dividend and distributions payable		79,518	85,138
Security deposits		63,872	67,927
Liabilities related to assets held for sale		265,538	4,074
Junior subordinated deferrable interest debentures held by trusts that issued trust preferred securities		100,000	100,000
Total liabilities	[1]	6,683,877	6,629,761
Commitments and contingencies
Noncontrolling interests in Operating Partnership		486,610	461,954
Preferred units		301,385	301,735
Equity
Series I Preferred Stock, $0.01 par value, $25.00 liquidation preference, 9,200 issued and outstanding at both June 30, 2018 and December 31, 2017		221,932	221,932
Common stock, $0.01 par value, 160,000 shares authorized and 86,780 and 93,858 issued and outstanding at June 30, 2018 and December 31, 2017, respectively (including 1,055 shares held in treasury at June 30, 2018 and December 31, 2017)		868	939
Additional paid-in-capital		4,601,608	4,968,338
Treasury stock at cost		(124,049)	(124,049)
Accumulated other comprehensive income		32,622	18,604
Retained earnings		1,457,835	1,139,329
Total SL Green stockholders' equity		6,190,816	6,225,093
Noncontrolling interests in other partnerships		51,240	364,361
Total equity		6,242,056	6,589,454
SL Green stockholders equity:
Total liabilities and equity/capital		13,713,928	13,982,904
SL Green Operating Partnership
Commercial real estate properties, at cost:
Land and land interests		1,893,047	2,357,051
Building and improvements		5,225,431	6,351,012
Building leasehold and improvements		1,423,994	1,450,614
Properties under capital lease		47,445	47,445
Total commercial real estate properties, at cost		8,589,917	10,206,122
Less: accumulated depreciation		(1,994,696)	(2,300,116)
Total commercial real estate properties, net		6,595,221	7,906,006
Assets held for sale		593,995	338,354
Cash and cash equivalents		287,240	127,888
Restricted cash		92,740	122,138
Investments in marketable securities		28,570	28,579
Tenant and other receivables, net of allowance of $16,558 and $18,637 in 2018 and 2017, respectively		47,482	57,644
Related party receivables		27,854	23,039
Deferred rents receivable, net of allowance of $15,776 and $17,207 in 2018 and 2017, respectively		322,656	365,337
Debt and preferred equity investments, net of discounts and deferred origination fees of $23,216 and $25,507 in 2018 and 2017, respectively		2,168,515	2,114,041
Investments in unconsolidated joint ventures		3,059,985	2,362,989
Deferred costs, net		198,941	226,201
Other assets		290,729	310,688
Total assets	[2]	13,713,928	13,982,904
Liabilities
Mortgages and other loans payable, net		2,517,097	2,837,282
Revolving credit facility, net		351,272	30,336
Unsecured term loan, net		1,492,320	1,491,575
Unsecured notes, net		1,396,722	1,395,939
Accrued interest payable		26,104	38,142
Other liabilities		108,151	188,005
Accounts payable and accrued expenses		140,739	137,142
Deferred revenue		95,756	208,119
Capital lease obligations		43,221	42,843
Deferred land leases payable		3,567	3,239
Dividend and distributions payable		79,518	85,138
Security deposits		63,872	67,927
Liabilities related to assets held for sale		265,538	4,074
Junior subordinated deferrable interest debentures held by trusts that issued trust preferred securities		100,000	100,000
Total liabilities	[2]	6,683,877	6,629,761
Commitments and contingencies
Noncontrolling interests in Operating Partnership		486,610	461,954
Limited partner interests in SLGOP (4,700 and 4,453 limited partner common units outstanding at June 30, 2018 and December 31, 2017, respectively)		486,610	461,954
Preferred units		301,385	301,735
Equity
Accumulated other comprehensive income		32,622	18,604
SL Green stockholders equity:
Series I Preferred Units, $25.00 liquidation preference, 9,200 issued and outstanding at both June 30, 2018 and December 31, 2017		221,932	221,932
SL Green partners' capital (904 and 973 general partner common units and 84,821 and 91,831 limited partner common units outstanding at June 30, 2018 and December 31, 2017, respectively)		5,936,262	5,984,557
Total SLGOP partners' capital		6,190,816	6,225,093
Noncontrolling interests in other partnerships		51,240	364,361
Total capital		6,242,056	6,589,454
Total liabilities and equity/capital		$ 13,713,928	$ 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: $175.0 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, $32.2 million and $330.9 million of accumulated depreciation, $860.2 million and $221.0 million of other assets included in other line items, $136.2 million and $628.9 million of real estate debt, net, $0.4 million and $2.5 million of accrued interest payable, $43.2 million and $42.8 million of capital lease obligations, and $155.6 million and $56.8 million of other liabilities included in other line items as of June 30, 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, excluding the Operating Partnership: $175.0 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, $32.2 million and $330.9 million of accumulated depreciation, $860.2 million and $221.0 million of other assets included in other line items, $136.2 million and $628.9 million of real estate debt, net, $0.4 million and $2.5 million of accrued interest payable, $43.2 million and $42.8 million of capital lease obligations, and $155.6 million and $56.8 million of other liabilities included in other line items as of June 30, 2018 and December 31, 2017, respectively.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Tenant and other receivables, allowance	$ 16,558	$ 18,637
Deferred rents receivable, allowance	15,776	17,207
Debt and preferred equity investments, discount and deferred origination fees	$ 23,216	$ 25,507
Preferred stock, par value (in dollars per share)	$ 0.01
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)	86,780,000	93,858,000
Common stock, shares outstanding (in shares)	86,780,000	93,858,000
Treasury stock, shares (in shares)	1,055,000	1,055,000
Land and land interests	$ 1,893,047	$ 2,357,051
Building and improvements	5,225,431	6,351,012
Building leasehold and improvements	1,423,994	1,450,614
Properties under capital lease	47,445	47,445
Accumulated depreciation	1,994,696	2,300,116
Other assets	290,729	310,688
Mortgages and other loans payable, net	2,517,097	2,837,282
Accrued interest payable	26,104	38,142
Capital lease obligations	43,221	42,843
Other liabilities	$ 108,151	$ 188,005
Series I Preferred Stock
Preferred stock, par value (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
Consolidated VIEs
Land and land interests	$ 175,000	$ 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	32,200	330,900
Other assets	860,200	221,000
Mortgages and other loans payable, net	136,200	628,900
Accrued interest payable	400	2,500
Capital lease obligations	43,200	42,800
Other liabilities	155,600	56,800
SL Green Operating Partnership
Tenant and other receivables, allowance	16,558	18,637
Deferred rents receivable, allowance	15,776	17,207
Debt and preferred equity investments, discount and deferred origination fees	$ 23,216	$ 25,507
Limited partner interests in Operating Partnership, limited partner common units outstanding (shares)	4,700,000	4,453,000
SL Green partner's capital, general partner common units outstanding (shares)	904,000	973,000
SL Green partners' capital, limited partner common units outstanding (shares)	84,821,000	91,831,000
Land and land interests	$ 1,893,047	$ 2,357,051
Building and improvements	5,225,431	6,351,012
Building leasehold and improvements	1,423,994	1,450,614
Properties under capital lease	47,445	47,445
Accumulated depreciation	1,994,696	2,300,116
Other assets	290,729	310,688
Mortgages and other loans payable, net	2,517,097	2,837,282
Accrued interest payable	26,104	38,142
Capital lease obligations	43,221	42,843
Other liabilities	$ 108,151	$ 188,005
SL Green Operating Partnership | Series I Preferred Stock
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 Operating Partnership | Consolidated VIEs
Land and land interests	$ 175,000	$ 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	32,200	330,900
Other assets	860,200	221,000
Mortgages and other loans payable, net	136,200	628,900
Accrued interest payable	400	2,500
Capital lease obligations	43,200	42,800
Other liabilities	$ 155,600	$ 56,800

Consolidated Statements of Oper

Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues
Rental revenue, net	$ 211,369	$ 279,407	$ 426,738	$ 560,736
Escalation and reimbursement	27,052	42,620	53,451	86,812
Investment income	49,273	60,622	94,563	100,921
Other income	13,422	15,501	28,059	27,062
Total revenues	301,116	398,150	602,811	775,531
Expenses
Operating expenses, including related party expenses of $4,665 and $8,499 in 2018 and $5,262 and $9,436 in 2017, respectively.	56,237	70,852	116,019	145,358
Real estate taxes	45,322	60,945	90,983	122,013
Ground rent	8,846	8,308	17,154	16,616
Interest expense, net of interest income	53,611	64,856	101,527	130,478
Amortization of deferred financing costs	3,546	3,432	7,083	8,193
Depreciation and amortization	67,914	133,054	137,302	227,188
Transaction related costs	348	46	510	179
Marketing, general and administrative	22,479	24,256	46,007	48,399
Total expenses	258,303	365,749	516,585	698,424
Net income before equity in net income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities	42,813	32,401	86,226	77,107
Equity in net income from unconsolidated joint ventures	4,702	3,412	8,738	10,026
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	72,025	13,089	65,585	15,136
Purchase price and other fair value adjustments	11,149	0	60,442	0
(Loss) gain on sale of real estate, net	(14,790)	(3,823)	8,731	(3,256)
Depreciable real estate reserves	0	(29,064)	0	(85,336)
Gain on sale of investment in marketable securities	0	0	0	3,262
Net income	115,899	16,015	229,722	16,939
Net (income) loss attributable to noncontrolling interests:
Noncontrolling interests in the Operating Partnership	(5,586)	(419)	(10,858)	(895)
Noncontrolling interests in other partnerships	(173)	(786)	(371)	16,705
Preferred units distributions	(2,847)	(2,851)	(5,696)	(5,701)
Net income (loss) attributable to SL Green/SLGOP	107,293	11,959	212,797	27,048
Perpetual preferred stock dividends	(3,737)	(3,737)	(7,475)	(7,475)
Amounts attributable to SL Green common stockholders:
Income before depreciable real estate reserves and gains on sale and fair value adjustments	38,674	27,156	77,333	89,818
Purchase price and other fair value adjustments	10,578	0	57,406	0
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	68,336	12,517	62,291	14,474
(Loss) gain on sale of real estate, net	(14,032)	(3,656)	8,292	(3,114)
Depreciable real estate reserves	0	(27,795)	0	(81,605)
Net income attributable to SL Green common stockholders	$ 103,556	$ 8,222	$ 205,322	$ 19,573
Basic earnings per share:
Income (loss) before depreciable real estate reserves and gains (losses) on sale (in dollars per share)	$ 0.44	$ 0.27	$ 0.87	$ 0.90
Purchase price and other fair value adjustments (in dollars per share)	0.12	0	0.65	0
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (in dollars per share)	0.79	0.13	0.70	0.14
Gain on sale of real estate, net (in dollars per share)	(0.16)	(0.04)	0.09	(0.03)
Depreciable real estate reserves (in dollars per share)	0	(0.28)	0	(0.81)
Net income attributable to SL Green common stockholders (usd per share)	1.19	0.08	2.31	0.20
Diluted earnings per share:
Purchase price and other fair value adjustments (in dollars per share)	0.12	0	0.65	0
Income (loss) before depreciable real estate reserves and gains (losses) on sale (in dollars per share)	0.44	0.27	0.87	0.89
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (in dollars per share)	0.79	0.12	0.70	0.14
Gain on sale of real estate (in dollars per share)	(0.16)	(0.04)	0.09	(0.03)
Depreciable real estate reserves (in dollars per share)	0	(0.27)	0	(0.81)
Net income attributable to SL Green common stockholders (usd per share)	1.19	0.08	2.31	0.19
Dividends per share/unit (usd per share)	$ 0.8125	$ 0.775	$ 1.625	$ 1.55
Basic weighted average common shares outstanding (in shares)	87,176	99,900	88,772	100,268
Diluted weighted average common shares and common share equivalents outstanding (in shares)	92,083	104,732	93,667	105,140
SL Green Operating Partnership
Revenues
Rental revenue, net	$ 211,369	$ 279,407	$ 426,738	$ 560,736
Escalation and reimbursement	27,052	42,620	53,451	86,812
Investment income	49,273	60,622	94,563	100,921
Other income	13,422	15,501	28,059	27,062
Total revenues	301,116	398,150	602,811	775,531
Expenses
Operating expenses, including related party expenses of $4,665 and $8,499 in 2018 and $5,262 and $9,436 in 2017, respectively.	56,237	70,852	116,019	145,358
Real estate taxes	45,322	60,945	90,983	122,013
Ground rent	8,846	8,308	17,154	16,616
Interest expense, net of interest income	53,611	64,856	101,527	130,478
Amortization of deferred financing costs	3,546	3,432	7,083	8,193
Depreciation and amortization	67,914	133,054	137,302	227,188
Transaction related costs	348	46	510	179
Marketing, general and administrative	22,479	24,256	46,007	48,399
Total expenses	258,303	365,749	516,585	698,424
Net income before equity in net income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities	42,813	32,401	86,226	77,107
Equity in net income from unconsolidated joint ventures	4,702	3,412	8,738	10,026
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	72,025	13,089	65,585	15,136
Purchase price and other fair value adjustments	11,149	0
(Loss) gain on sale of real estate, net	(14,790)	(3,823)	8,731	(3,256)
Depreciable real estate reserves	0	(29,064)	0	(85,336)
Gain on sale of investment in marketable securities	0	0	0	3,262
Net income	115,899	16,015	229,722	16,939
Net (income) loss attributable to noncontrolling interests:
Noncontrolling interests in the Operating Partnership			(10,858)
Noncontrolling interests in other partnerships	(173)	(786)	(371)	16,705
Preferred units distributions	(2,847)	(2,851)	(5,696)	(5,701)
Net income (loss) attributable to SL Green/SLGOP	112,879	12,378	223,655	27,943
Perpetual preferred unit distributions	(3,737)	(3,737)	(7,475)	(7,475)
Net income attributable to SLGOP common unitholders	109,142	8,641	216,180	20,468
Amounts attributable to SL Green common stockholders:
Income before depreciable real estate reserves and gains on sale and fair value adjustments	40,758	28,439	81,422	93,924
Purchase price and other fair value adjustments	11,149	0	60,442	0
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	72,025	13,089	65,585	15,136
(Loss) gain on sale of real estate, net	(14,790)	(3,823)	8,731	(3,256)
Depreciable real estate reserves	$ 0	$ (29,064)	$ 0	$ (85,336)
Basic earnings per share:
Income (loss) before depreciable real estate reserves and gains (losses) on sale (in dollars per share)	$ 0.44	$ 0.27	$ 0.87	$ 0.90
Purchase price and other fair value adjustments (in dollars per share)	0.12	0	0.65	0
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (in dollars per share)	0.79	0.13	0.70	0.14
Gain on sale of real estate, net (in dollars per share)	(0.16)	(0.04)	0.09	(0.03)
Depreciable real estate reserves (in dollars per share)	0	(0.28)	0	(0.81)
Net income attributable to SLGOP common unitholders (usd per share)	1.19	0.08	2.31	0.20
Diluted earnings per share:
Income (loss) before depreciable real estate reserves and gains (losses) on sale (in dollars per share)	0.44	0.27	0.87	0.89
Purchase price and other fair value adjustments (in dollars per share)	0.12	0	0.65	0
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (in dollars per share)	0.79	0.12	0.70	0.14
Gain on sale of real estate (in dollars per share)	(0.16)	(0.04)	0.09	(0.03)
Depreciable real estate reserves (in dollars per share)	0	(0.27)	0	(0.81)
Net income attributable to SLGOP common unitholders (usd per share)	1.19	0.08	2.31	0.19
Dividends per share/unit (usd per share)	$ 0.8125	$ 0.775	$ 1.625	$ 1.55
Basic weighted average common shares outstanding (in shares)	91,882	104,462	93,467	104,852
Basic weighted average common units outstanding (in shares)	91,882	104,462	93,467	104,852
Diluted weighted average common units and common unit equivalents outstanding (in shares)	92,083	104,732	93,667	105,140

Consolidated Statements of Ope5

Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating expenses, paid to related parties	$ 4,655	$ 8,499	$ 5,262	$ 9,436
SL Green Operating Partnership
Operating expenses, paid to related parties	$ 4,665	$ 8,499	$ 5,262	$ 9,436

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income	$ 115,899	$ 16,015	$ 229,722	$ 16,939
Other comprehensive income (loss):
Change in net unrealized gain on derivative instruments, including SL Green's/SLGOP's share of joint venture net unrealized (loss) gain on derivative instruments	3,977	(2,520)	14,890	(3,595)
Change in unrealized gain (loss) on marketable securities	318	263	(8)	(4,487)
Other comprehensive income (loss)	4,295	(2,257)	14,882	(8,082)
Comprehensive income	120,194	13,758	244,604	8,857
Net (income) loss attributable to noncontrolling interests and preferred units distributions	(8,606)	(4,056)	(16,925)	10,109
Net (loss) income attributable to noncontrolling interests	(173)	(786)	(371)	16,705
Other comprehensive (loss) income attributable to noncontrolling interests	(245)	100	(864)	299
Comprehensive income attributable to SL Green/SLGOP	111,343	9,802	226,815	19,265
SL Green Operating Partnership
Net income	115,899	16,015	229,722	16,939
Other comprehensive income (loss):
Change in net unrealized gain on derivative instruments, including SL Green's/SLGOP's share of joint venture net unrealized (loss) gain on derivative instruments	3,977	(2,520)	14,890	(3,595)
Change in unrealized gain (loss) on marketable securities	318	263	(8)	(4,487)
Other comprehensive income (loss)	4,295	(2,257)	14,882	(8,082)
Comprehensive income	120,194	13,758	244,604	8,857
Net (loss) income attributable to noncontrolling interests	(173)	(786)	(371)	16,705
Other comprehensive (loss) income attributable to noncontrolling interests	(245)	100	(864)	299
Comprehensive income attributable to SL Green/SLGOP	$ 119,776	$ 13,072	$ 243,369	$ 25,861

Consolidated Statement of Equit

Consolidated Statement of Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In-Capital	Treasury Stock	Accumulated Other Comprehensive Income	Retained Earnings	Noncontrolling Interests	Series I Preferred StockPreferred Stock
Increase (Decrease) in Stockholders' Equity
Cumulative adjustment upon adoption of ASC 610-20 | Accounting Standards Update 2014-09	$ 570,524						$ 570,524
Beginning Balance at Dec. 31, 2017	6,589,454		$ 939	$ 4,968,338	$ (124,049)	$ 18,604	1,139,329	$ 364,361	$ 221,932
Beginning Balance (in shares) at Dec. 31, 2017			92,803
Adjusted Balance at Dec. 31, 2017	7,159,978		$ 939	4,968,338	(124,049)	18,604	1,709,853	364,361	$ 221,932
Increase (Decrease) in Stockholders' Equity
Net income	213,168						212,797	371
Other comprehensive income	14,018					14,018
Preferred dividends	(7,475)						(7,475)
DRSPP proceeds (in shares)			1
DRSPP proceeds	64			64
Conversion of units of the Operating Partnership to common stock (in shares)			15
Conversion of units in the Operating Partnership for common stock	1,560			1,560
Reallocation of noncontrolling interest in the Operating Partnership	(4,493)						(4,493)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)			(20)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	8,090			8,090
Repurchases of common stock (in shares)			(7,133)
Repurchases of common stock	(693,091)		$ (72)	(382,080)			(310,939)
Proceeds from stock options exercised (in shares)			59
Proceeds from stock options exercised	5,637		$ 1	5,636
Contributions to consolidated joint venture interests	1,828							1,828
Deconsolidation of partially owned entity	(314,596)							(314,596)
Cash distributions to noncontrolling interests	(724)							(724)
Cash distributions declared ($1.625 per common share, none of which represented a return of capital for federal income tax purposes)	(141,908)						(141,908)
Ending Balance at Jun. 30, 2018	$ 6,242,056	$ 221,932	$ 868	$ 4,601,608	$ (124,049)	$ 32,622	$ 1,457,835	$ 51,240
Ending Balance (in shares) at Jun. 30, 2018			85,725

Consolidated Statement of Equi8

Consolidated Statement of Equity (Parenthetical) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Stockholders' Equity [Abstract]
Cash distribution declared, per common share (in dollars per share)	$ 0.8125	$ 0.775	$ 1.625	$ 1.55

Consolidated Statement of Capit

Consolidated Statement of Capital (Unaudited) - USD ($) shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Increase (Decrease) in Partner's Capital
DRSPP proceeds	$ 64
Conversion of common units	1,560
Reallocation of noncontrolling interests in the operating partnership	(4,493)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	8,090
Repurchases of common stock	(693,091)
Contribution to consolidated joint venture interests	1,828
Deconsolidation of partially owned entity	(314,596)
Cash distributions to noncontrolling interests	$ (724)
Common Stock
Increase (Decrease) in Partner's Capital
DRSPP proceeds (in shares)	1
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)	(20)
Repurchases of common stock (in shares)	(7,133)
Repurchases of common stock	$ (72)
Contributions - proceeds from stock options exercised (in shares)	59
Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Contribution to consolidated joint venture interests	$ 1,828
Deconsolidation of partially owned entity	(314,596)
Cash distributions to noncontrolling interests	(724)
SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Beginning Balance	6,589,454
Adjusted Balance	7,159,978
Net income	213,168
Other comprehensive income	14,018
Preferred distributions	(7,475)
DRSPP proceeds	64
Conversion of common units	1,560
Reallocation of noncontrolling interests in the operating partnership	(4,493)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	8,090
Repurchases of common stock	(693,091)
Contribution to consolidated joint venture interests	1,828
Deconsolidation of partially owned entity	(314,596)
Contributions - proceeds from stock options exercised	5,637
Cash distributions to noncontrolling interests	(724)
Cash distributions declared ($1.625 per common unit, none of which represented a return of capital for federal income tax purposes)	(141,908)
Ending Balance	6,242,056
SL Green Operating Partnership | Common Stock | Partners' Interest
Increase (Decrease) in Partner's Capital
Beginning Balance	$ 5,984,557
Beginning Balance (units)	92,803
Adjusted Balance	$ 6,555,081
Net income	212,797
Preferred distributions	$ (7,475)
DRSPP proceeds (in shares)	1
DRSPP proceeds	$ 64
Conversion of common units (in shares)	15
Conversion of common units	$ 1,560
Reallocation of noncontrolling interests in the operating partnership	$ (4,493)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)	(20)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	$ 8,090
Repurchases of common stock (in shares)	(7,133)
Repurchases of common stock	$ (693,091)
Contributions - proceeds from stock options exercised (in shares)	59
Contributions - proceeds from stock options exercised	$ 5,637
Cash distributions declared ($1.625 per common unit, none of which represented a return of capital for federal income tax purposes)	(141,908)
Ending Balance	$ 5,936,262
Ending Balance (units)	85,725
SL Green Operating Partnership | Accumulated Other Comprehensive Income
Increase (Decrease) in Partner's Capital
Beginning Balance	$ 18,604
Adjusted Balance	18,604
Other comprehensive income	14,018
Ending Balance	32,622
SL Green Operating Partnership | Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Beginning Balance	364,361
Adjusted Balance	364,361
Net income	371
Contribution to consolidated joint venture interests	1,828
Deconsolidation of partially owned entity	(314,596)
Cash distributions to noncontrolling interests	(724)
Ending Balance	51,240
Series I Preferred Stock | SL Green Operating Partnership | Preferred Units
Increase (Decrease) in Partner's Capital
Beginning Balance	221,932
Adjusted Balance	221,932
Ending Balance	$ 221,932
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 Cap10

Consolidated Statement of Capital (Parenthetical) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Cash distribution declared, per common share (in dollars per share)	$ 0.8125	$ 0.775	$ 1.625	$ 1.55
SL Green Operating Partnership
Cash distribution declared, per common share (in dollars per share)	$ 0.8125	$ 0.775	$ 1.625	$ 1.55

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating Activities
Net income	$ 229,722	$ 16,939
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	144,385	235,381
Equity in net income from unconsolidated joint ventures	(8,738)	(10,026)
Distributions of cumulative earnings from unconsolidated joint ventures	9,889	12,388
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(65,585)	(15,136)
Purchase price and other fair value adjustments	(60,442)	0
Depreciable real estate reserves	0	85,336
(Gain) loss on sale of real estate, net	(8,731)	3,256
Gain on sale of investments in marketable securities	0	(3,262)
Deferred rents receivable	(4,369)	(23,237)
Other non-cash adjustments	9,404	20,352
Changes in operating assets and liabilities:
Tenant and other receivables	(397)	1,447
Related party receivables	(1,116)	(7,869)
Deferred lease costs	(17,469)	(23,560)
Other assets	(4,329)	680
Accounts payable, accrued expenses, other liabilities and security deposits	22,867	(11,310)
Deferred revenue and land leases payable	1,121	29,471
Net cash provided by operating activities	246,212	310,850
Investing Activities
Acquisitions of real estate property	(9,733)	(19)
Additions to land, buildings and improvements	(96,577)	(165,262)
Acquisition deposits and deferred purchase price	(1,520)	0
Investments in unconsolidated joint ventures	(254,305)	(93,182)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	178,892	93,688
Net proceeds from disposition of real estate/joint venture interest	760,335	61,248
Proceeds from sale or redemption of marketable securities	0	54,363
Other investments	(22,790)	3,014
Origination of debt and preferred equity investments	(603,575)	(854,577)
Repayments or redemption of debt and preferred equity investments	317,337	663,140
Net cash provided by (used in) investing activities	268,064	(237,587)
Financing Activities
Proceeds from mortgages and other loans payable	210,575	779,642
Repayments of mortgages and other loans payable	(22,864)	(693,243)
Proceeds from revolving credit facility and senior unsecured notes	1,475,000	1,072,800
Repayments of revolving credit facility and senior unsecured notes	(1,155,000)	(875,697)
Proceeds from stock options exercised and DRIP issuance	5,701	11,706
Repurchase of common stock	(724,696)	(211,599)
Redemption of preferred stock	(350)	(125)
Distributions to noncontrolling interests in other partnerships	(724)	(609)
Contributions from noncontrolling interests in other partnerships	1,828	33,009
Distributions to noncontrolling interests in the Operating Partnership	(7,712)	(7,112)
Dividends / Distributions paid on common and preferred stock / units	(160,699)	(168,678)
Other obligations related to loan participations	(3)	10,000
Tax withholdings related to restricted share awards	(3,842)	(3,879)
Deferred loan costs and capitalized lease obligation	(1,536)	(8,521)
Net cash used in financing activities	(384,322)	(62,306)
Net increase in cash, cash equivalents, and restricted cash	129,954	10,957
Cash, cash equivalents, and restricted cash at end of period	379,980	380,924
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Conversion of units in the Operating Partnership for common stock	1,560	13,242
Tenant improvements and capital expenditures payable	16,534	7,210
Fair value adjustment to noncontrolling interest in Operating Partnership	4,493	12,712
Deconsolidation of subsidiaries	298,403	328,644
Transfer of assets related to assets held for sale	593,995	173,918
Transfer of liabilities related to assets held for sale	265,538	149
Removal of fully depreciated commercial real estate properties	110,594	5,754
Share repurchase payable	31,605	41,598
Bond repurchase payable	0	65,416
Total cash, cash equivalents, and restricted cash	379,980	380,924
SL Green Operating Partnership
Operating Activities
Net income	229,722	16,939
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	144,385	235,381
Equity in net income from unconsolidated joint ventures	(8,738)	(10,026)
Distributions of cumulative earnings from unconsolidated joint ventures	9,889	12,388
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(65,585)	(15,136)
Purchase price and other fair value adjustments	(60,442)	0
Depreciable real estate reserves	0	85,336
(Gain) loss on sale of real estate, net	(8,731)	3,256
Gain on sale of investments in marketable securities	0	(3,262)
Deferred rents receivable	(4,369)	(23,237)
Other non-cash adjustments	9,404	20,352
Changes in operating assets and liabilities:
Tenant and other receivables	(397)	1,447
Related party receivables	(1,116)	(7,869)
Deferred lease costs	(17,469)	(23,560)
Other assets	(4,329)	680
Accounts payable, accrued expenses, other liabilities and security deposits	22,867	(11,310)
Deferred revenue and land leases payable	1,121	29,471
Net cash provided by operating activities	246,212	310,850
Investing Activities
Acquisitions of real estate property	(9,733)	(19)
Additions to land, buildings and improvements	(96,577)	(165,262)
Acquisition deposits and deferred purchase price	(1,520)	0
Investments in unconsolidated joint ventures	(254,305)	(93,182)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	178,892	93,688
Net proceeds from disposition of real estate/joint venture interest	760,335	61,248
Proceeds from sale or redemption of marketable securities	0	54,363
Other investments	(22,790)	3,014
Origination of debt and preferred equity investments	(603,575)	(854,577)
Repayments or redemption of debt and preferred equity investments	317,337	663,140
Net cash provided by (used in) investing activities	268,064	(237,587)
Financing Activities
Proceeds from mortgages and other loans payable	210,575	779,642
Repayments of mortgages and other loans payable	(22,864)	(693,243)
Proceeds from revolving credit facility and senior unsecured notes	1,475,000	1,072,800
Repayments of revolving credit facility and senior unsecured notes	(1,155,000)	(875,697)
Proceeds from stock options exercised and DRIP issuance	5,701	11,706
Repurchase of common stock	(724,696)	(211,599)
Redemption of preferred stock	(350)	(125)
Distributions to noncontrolling interests in other partnerships	(724)	(609)
Contributions from noncontrolling interests in other partnerships	1,828	33,009
Dividends / Distributions paid on common and preferred stock / units	(168,411)	(175,790)
Tax withholdings related to restricted share awards	(3,842)	(3,879)
Deferred loan costs and capitalized lease obligation	(1,536)	(8,521)
Net cash used in financing activities	(384,322)	(62,306)
Net increase in cash, cash equivalents, and restricted cash	129,954	10,957
Cash, cash equivalents, and restricted cash at beginning of year	250,026	369,967
Cash, cash equivalents, and restricted cash at end of period	379,980	380,924
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Conversion of units in the Operating Partnership for common stock	1,560	13,242
Tenant improvements and capital expenditures payable	16,534	7,210
Fair value adjustment to noncontrolling interest in Operating Partnership	4,493	12,712
Deconsolidation of subsidiaries	298,403	328,644
Transfer of assets related to assets held for sale	593,995	173,918
Transfer of liabilities related to assets held for sale	265,538	149
Removal of fully depreciated commercial real estate properties	110,594	5,754
Share repurchase payable	31,605	41,598
Bond repurchase payable	0	65,416
Total cash, cash equivalents, and restricted cash	$ 250,026	$ 369,967

Organization and Basis of Prese

Organization and Basis of Presentation	6 Months Ended
	Jun. 30, 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 June 30, 2018 , noncontrolling investors held, in the aggregate, a 5.20% 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 June 30, 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 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 21 (2) 12,756,091 10 11,491,164 31 24,247,255 94.1 % Retail 4 (3) 302,583 9 347,970 13 650,553 94.2 % Development/Redevelopment 8 318,985 3 416,214 11 735,199 43.9 % Fee Interest — — 1 — 1 — — % 33 13,377,659 23 12,255,348 56 25,633,007 92.6 % Suburban Office 19 (4) 2,835,200 — — 19 2,835,200 87.0 % Retail 1 52,000 — — 1 52,000 100.0 % Development/Redevelopment 1 1,000 — — 1 1,000 — % 21 2,888,200 — — 21 2,888,200 87.2 % Total commercial properties 54 16,265,859 23 12,255,348 77 28,521,207 92.1 % Residential: Manhattan Residential 3 (3) 472,105 10 2,156,751 13 2,628,856 90.0 % Suburban Residential — — — — — — — % Total residential properties 3 472,105 10 2,156,751 13 2,628,856 90.0 % Total portfolio 57 16,737,964 33 14,412,099 90 31,150,063 91.9 % (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) Includes 2 Herald Square, which is under contract for sale of a joint venture interest and has been classified as held for sale as of June 30, 2018 . (3) As of June 30, 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. (4) Includes the properties at 1-6 International Drive in Rye Brook, New York which are classified as held for sale at June 30, 2018 . As of June 30, 2018 , we also managed an approximately 336,000 square foot (unaudited) office building owned by a third party and held debt and preferred equity investments with a book value of $2.4 billion , including $0.2 billion of debt and preferred equity investments and other financing receivables that are included in balance sheet line items other than the Debt and Preferred Equity Investments line item. Partnership Agreement In accordance with the partnership agreement of the Operating Partnership, or the Operating Partnership Agreement, we allocate all distributions and profits and losses in proportion to the percentage of ownership interests of the respective partners. As the managing general partner of the Operating Partnership, we are required to take such reasonable efforts, as determined by us in our sole discretion, to cause the Operating Partnership to distribute sufficient amounts to enable the payment of sufficient dividends by us to minimize any Federal income or excise tax at the Company level. Under the Operating Partnership Agreement, each limited partner has the right to redeem units of limited partnership interests for cash, or if we so elect, shares of SL Green's common stock on a one-for- one basis. Basis of Quarterly Presentation The accompanying unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and notes required by accounting principles generally accepted in the United States for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for the fair presentation of the financial position of the Company and the Operating Partnership at June 30, 2018 and the results of operations for the periods presented have been included. The operating results for the period presented are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 . These financial statements should be read in conjunction with the financial statements and accompanying notes included in the Annual Report on Form 10-K for the year ended December 31, 2017 of the Company and the Operating Partnership. The consolidated balance sheet at December 31, 2017 has been derived from the audited financial statements as of that date but does not include all the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements. Subsequent Events In August 2018, the Operating Partnership issued $350.0 million of senior unsecured notes, with the Company and ROP as guarantors. The notes bear interest at a floating rate, reset quarterly, equal to three-month LIBOR plus 98 basis points. The notes will mature in August 2021 and can be redeemed at par beginning in August 2019.

Significant Accounting Policies

Significant Accounting Policies	6 Months Ended
	Jun. 30, 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 variable interest entity, or VIE, in which we are considered the primary beneficiary. The primary beneficiary is the entity that has (i) the power to direct the activities that most significantly impact the entity's economic performance and (ii) the obligation to absorb losses of the VIE or the right to receive benefits from the VIE that could be significant to the VIE. Investment in Commercial Real Estate Properties 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. On a periodic basis, we assess whether there are any indications that the value of our real estate properties may be other than temporarily impaired or that their carrying value may not be recoverable. A property's value is considered impaired if management's estimate of the aggregate future cash flows (undiscounted) to be generated by the property is less than the carrying value of the property. To the extent impairment has occurred, the loss will be measured as the excess of the carrying amount of the property over the calculated fair value of the property. We also evaluate our real estate properties for impairment when a property has been classified as held for sale. Real estate assets held for sale are valued at the lower of their carrying value or fair value less costs to sell. We recognized $1.8 million and $4.2 million of rental revenue for the three and six months ended June 30, 2018 and $6.4 million and $11.2 million for the three and six months ended June 30, 2017 , 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. For the three and six months ended June 30, 2018 we recognized as a reduction to interest expense the amortization of above-market rate mortgages of $0.0 million and $0.0 million , respectively. For the three and six months ended June 30, 2017 we recognized as a reduction to interest expense the amortization of above-market rate mortgages of $0.7 million and $1.3 million , 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 June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Identified intangible assets (included in other assets): Gross amount $ 263,138 $ 325,880 Accumulated amortization (239,344 ) (277,038 ) Net (1) $ 23,794 $ 48,842 Identified intangible liabilities (included in deferred revenue): Gross amount $ 274,120 $ 540,283 Accumulated amortization (249,905 ) (402,583 ) Net (1) $ 24,215 $ 137,700 (1) As of June 30, 2018 and December 31, 2017, $0.1 million and $13.9 million , respectively and $0.1 million and $4.1 million , respectively, of net intangible assets and net intangible liabilities, were reclassified to assets held for sale and liabilities related to assets held for sale. Fair Value Measurements See Note 16, "Fair Value Measurements." Investment in Marketable Securities At acquisition, we designate a debt security as held-to-maturity, available-for-sale, or trading. As of June 30, 2018 , we did not have any debt securities designated as held-to-maturity or trading. We account for our available-for-sale debt securities at fair value pursuant to Accounting Standards Codification, or ASC, 820-10, with the net unrealized gains or losses reported as a component of accumulated other comprehensive income or loss. Any unrealized losses that are determined to be other-than-temporary are recognized in earnings up to their credit component. The 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 June 30, 2018 . The cost of bonds and marketable securities sold is determined using the specific identification method. At June 30, 2018 and December 31, 2017 , we held the following marketable securities (in thousands): June 30, 2018 December 31, 2017 Commercial mortgage-backed securities $ 28,570 $ 28,579 Total marketable securities available-for-sale $ 28,570 $ 28,579 The cost basis of the commercial mortgage-backed securities was $27.5 million at both June 30, 2018 and December 31, 2017 . These securities mature at various times through 2035. We held no equity marketable securities as of June 30, 2018 and December 31, 2017 . During the three and six months ended June 30, 2018 , we did not dispose of any marketable securities. During the three months ended June 30, 2017 , we did not dispose of any marketable securities. During the six months ended June 30, 2017 , we disposed of marketable securities for aggregate net proceeds of $54.4 million and realized a gain of $3.3 million , which is included in gain on sale of investment in marketable securities on the consolidated statements of operations. 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 June 30, 2018 . Reserve for Possible Credit Losses The reserve for possible credit losses in connection with debt and preferred equity investments is the charge to earnings to increase the allowance for possible credit losses to the level that we estimate to be adequate, based on Level 3 data, considering delinquencies, loss experience and collateral quality. Other factors considered include geographic trends, product diversification, the size of the portfolio and current economic conditions. Based upon these factors, we establish a provision for possible credit loss on each individual investment. When it is probable that we will be unable to collect all amounts contractually due, the investment is considered impaired. Where impairment is indicated on an investment that is held to maturity, a valuation allowance is measured based upon the excess of the recorded investment amount over the fair value of the collateral. Any deficiency between the carrying amount of an asset and the calculated value of the collateral is charged to expense. We continue to assess or adjust our estimates based on circumstances of a loan and the underlying collateral. If additional information reflects increased recovery of our investment, we will adjust our reserves accordingly. There were no loan reserves recorded during the three and six months ended June 30, 2018 and 2017 . Debt and preferred equity investments held for sale are carried at the lower of cost or fair market value using available market information obtained through consultation with dealers or other originators of such investments as well as discounted cash flow models based on Level 3 data pursuant to ASC 820-10. As circumstances change, management may conclude not to sell an investment designated as held for sale. In such situations, the investment will be reclassified at its net carrying value to debt and preferred equity investments held to maturity. For these reclassified investments, the difference between the current carrying value and the expected cash to be collected at maturity will be accreted into income over the remaining term of the investment. Income Taxes SL Green is taxed as a REIT under Section 856(c) of the Code. As a REIT, SL Green generally is not subject to Federal income tax. To maintain its qualification as a REIT, SL Green must distribute at least 90% of its REIT taxable income to its stockholders and meet certain other requirements. If SL Green fails to qualify as a REIT in any taxable year, SL Green will be subject to Federal income tax on its taxable income at regular corporate rates. SL Green may also be subject to certain state, local and franchise taxes. Under certain circumstances, Federal income and excise taxes may be due on its undistributed taxable income. The Operating Partnership is a partnership and, as a result, all income and losses of the partnership are allocated to the partners for inclusion in their respective income tax returns. The only provision for income taxes included in the consolidated statements of operations relates to the Operating Partnership’s consolidated taxable REIT subsidiaries. The Operating Partnership may also be subject to certain state, local and franchise taxes. Pursuant to amendments to the Code that became effective January 1, 2001, we have elected, and may elect in the future, to treat certain of our existing or newly created corporate subsidiaries as taxable REIT subsidiaries, or TRSs. In general, TRSs may perform non-customary services for the tenants of the Company, hold assets that we cannot hold directly and generally may engage in any real estate or non-real estate related business. The TRSs generate income, resulting in Federal and state income tax liability for these entities. During the three and six months ended June 30, 2018 , we recorded Federal, state and local tax provisions of $1.1 million and $1.6 million , respectively. 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. Many of the provisions of the Tax Act will require guidance through the issuance of Treasury regulations in order to assess their effect. The Tax Act has not had a material impact on our financial statements. 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 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. Other than one tenant, Credit Suisse Securities (USA), Inc., who accounts for 8.2% of our share of annualized cash rent, no other tenant in our portfolio accounted for more than 5.0% of our share of annualized cash rent, including our share of joint venture annualized rent, at June 30, 2018 . For the three months ended June 30, 2018 , 7.3% , 7.2% , 6.4% , 5.8% and 5.7% of our annualized cash rent was attributable to 11 Madison Avenue, 1185 Avenue of the Americas, 420 Lexington Avenue, 1515 Broadway, and One Madison Avenue respectively. Annualized cash rent for all other consolidated properties was below 5.0% . Reclassification Certain prior year balances have been reclassified to conform to our current year presentation. Accounting Standards Updates In June 2018, the FASB issued Accounting Standard Update (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 will be effective for the Company for fiscal years beginning after December 15, 2018, including the interim periods within that fiscal year. 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 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 guidance will be effective for the Company in the interim period beginning after June 15, 2018. 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 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities. The amendments in the new standard will permit more flexibility in hedging interest rate risk for both variable rate and fixed rate financial instruments. The standard will also enhance the presentation of hedge results in the financial statements. The guidance is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. The Company has not yet adopted the guidance, and does not expect a material impact on the Company’s consolidated financial statements when the new standard is implemented. In May 2017, the FASB issued 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. 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 has not yet adopted this new guidance and is currently evaluating the impact of adopting this new accounting standard on the Company’s consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases, and in July 2018, the FASB issued ASU No. 2018-10, Codification Improvements to Topic 842, Leases and ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. 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 accounting applied by a lessor, inclusive of the effect of a 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 and to adopt, is largely unchanged from that applied under the previous standard. However, 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. The Company is currently quantifying these impacts. This guidance is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early adoption is permitted. The Company expects to adopt this guidance January 1, 2019 and will apply the modified retrospective approach. In January 2016, the FASB issued ASU 2016-01 (Subtopic 825-10), Recognition and Measurement of Financial Assets and Financial Liabilities. The guidance requires entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value through earnings, to record changes in 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.

Property Acquisitions

Property Acquisitions	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Property Acquisitions	Property Acquisitions The following table summarizes the properties acquired during the six months ended June 30, 2018 : Property Acquisition Date Property Type Approximate Square Feet Acquisition Price (in millions) 2 Herald Square (1) May 2018 Leasehold Interest 369,000 $ 266.0 (1) In May 2018, SL Green 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, which 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 $11.1 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." In May 2018, we entered into an agreement to sell a partial interest in 2 Herald Square resulting in the leasehold interest being classified as held for sale as of June 30, 2018 . See Note 4, "Property Dispositions."

Properties Held for Sale and Pr

Properties Held for Sale and Property Dispositions	6 Months Ended
	Jun. 30, 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 June 30, 2018 , 1-6 International Drive and 2 Herald Square were classified as held for sale. We closed on the sale of 1-6 International Drive in July 2018 . Property Dispositions The following table summarizes the properties sold during the six months ended June 30, 2018 : Property Disposition Date Property Type Approximate Square Feet Sales Price (1) (in millions) Gain (loss) (2) (in millions) 600 Lexington Avenue January 2018 Fee Interest 303,515 $ 305.0 $ 23.8 115-117 Stevens Avenue May 2018 Fee Interest 178,000 12.0 (0.7 ) 635 Madison Avenue June 2018 Fee Interest 176,530 153.0 (14.1 ) (1) Sales price represents the gross sales price for a property or the gross asset valuation for interests in a property. (2) Gain (loss) on sale amounts do not include adjustments for expenses recorded in subsequent periods.

Debt and Preferred Equity Inves

Debt and Preferred Equity Investments	6 Months Ended
	Jun. 30, 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 for the six months ended June 30, 2018 and the twelve months ended December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Balance at beginning of period (1) $ 2,114,041 $ 1,640,412 Debt investment originations/accretion (2) 611,686 1,142,591 Preferred equity investment originations/accretion (2) 4,177 144,456 Redemptions/sales/syndications/amortization (3) (561,389 ) (813,418 ) Balance at end of period (1) $ 2,168,515 $ 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 are included in other assets and other liabilities on the consolidated balance sheets. Debt Investments As of June 30, 2018 and December 31, 2017 , we held the following debt investments with an aggregate weighted average current yield of 9.06% at June 30, 2018 (in thousands): Loan Type June 30, 2018 June 30, 2018 Senior June 30, 2018 (1) December 31, 2017 (1) Maturity (2) Fixed Rate Investments: Mortgage Loan (3)(4) $ — $ — $ 26,394 $ 26,366 February 2019 Mortgage Loan — — 164 239 August 2019 Mezzanine Loan (5a) — 1,160,000 208,506 204,005 March 2020 Mezzanine Loan — 15,000 3,500 3,500 September 2021 Mezzanine Loan — 147,000 24,922 24,913 April 2022 Mezzanine Loan — 280,000 35,564 34,600 August 2022 Mezzanine Loan (6) — 86,201 12,702 12,699 November 2023 Mezzanine Loan (5b) — 115,000 12,936 12,932 June 2024 Mezzanine Loan — 95,000 30,000 30,000 January 2025 Mezzanine Loan — 340,000 15,000 15,000 November 2026 Mezzanine Loan — 1,657,500 55,250 55,250 June 2027 Mortgage/Jr. Mortgage Loan (7) — — — 250,464 Total fixed rate $ — $ 3,895,701 $ 424,938 $ 669,968 Floating Rate Investments: Mezzanine Loan — 20,523 10,970 10,934 August 2018 Mortgage/Mezzanine Loan (8) — — 19,990 19,940 August 2018 Mezzanine Loan (9) — 65,000 14,992 14,955 August 2018 Mortgage/Mezzanine Loan — — 16,992 16,969 September 2018 Mezzanine Loan (10) — 37,500 14,961 14,855 September 2018 Mezzanine Loan 2,325 45,025 35,072 34,879 October 2018 Mezzanine Loan (5c) — 150,000 15,347 15,381 December 2018 Mezzanine Loan (5d) — — 14,836 14,869 December 2018 Mezzanine Loan — 33,000 26,967 26,927 December 2018 Mezzanine Loan — 175,000 59,873 59,723 December 2018 Mezzanine Loan (11) — 45,000 12,211 12,174 January 2019 Mezzanine Loan 4,000 29,291 9,980 8,550 January 2019 Mezzanine Loan (5e)(12) 795 — 15,150 15,148 March 2019 Mezzanine Loan — 38,000 21,964 21,939 March 2019 Mezzanine Loan (13) — 40,000 19,958 19,982 April 2019 Mezzanine Loan (13) — 61,130 21,718 34,947 April 2019 Mezzanine Loan — 175,000 37,355 37,250 April 2019 Mezzanine Loan — 265,000 24,895 24,830 April 2019 Mortgage/Jr. Mortgage Participation Loan 20,065 220,572 79,551 71,832 August 2019 Mezzanine Loan (10) 2,034 189,829 37,884 37,851 September 2019 Mortgage/Mezzanine Loan 20,560 — 168,369 143,919 September 2019 Mezzanine Loan — 350,000 34,810 34,737 October 2019 Mortgage/Mezzanine Loan 1,306 — 46,168 — December 2019 Mortgage/Mezzanine Loan 17,627 — 51,981 43,845 January 2020 Mezzanine Loan 1,123 571,863 78,462 75,834 January 2020 Mortgage Loan 14,786 — 84,783 — February 2020 Mezzanine Loan 3,878 306,711 50,669 — March 2020 Mortgage/Mezzanine Loan 45,019 — 333,290 — April 2020 Mezzanine Loan 6,386 35,912 11,829 11,259 July 2020 Loan Type June 30, 2018 June 30, 2018 Senior June 30, 2018 (1) December 31, 2017 (1) Maturity (2) Mezzanine Loan 44,088 340,558 83,065 75,428 November 2020 Mortgage and Mezzanine Loan 38,200 — 93,498 88,989 December 2020 Mortgage and Mezzanine Loan — — 35,207 35,152 December 2020 Jr. Mortgage Participation/Mezzanine Loan — 60,000 15,648 15,635 July 2021 Mortgage/Mezzanine Loan (14) — — — 162,553 Mortgage/Mezzanine Loan (14) — — — 74,755 Mortgage/Mezzanine Loan (15) — — — 23,609 Total floating rate $ 222,192 $ 3,254,914 $ 1,598,445 $ 1,299,650 Total $ 222,192 $ 7,150,615 $ 2,023,383 $ 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) In September 2014, we acquired a $26.4 million mortgage loan at a $0.2 million discount and a $5.7 million junior mortgage participation at a $5.7 million discount. The junior mortgage participation has been a nonperforming loan since acquisition, is currently on non-accrual status and has no carrying value. (4) This loan was repaid in August 2018. (5) Carrying value is net of the following amounts that were sold or syndicated, which are included in other assets and other liabilities on the consolidated balance sheets as a result of the transfers not meeting the conditions for sale accounting: (a) $1.3 million , (b) $12.0 million , (c) $14.6 million , (d) $14.1 million , and (e) $5.1 million . (6) The loan's June interest payment was outstanding at June 30, 2018 and was subsequently received in July 2018. 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. (7) 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. (8) This loan was extended in August 2018. (9) This loan was extended in July 2018. (10) This loan was repaid in July 2018. (11) In July 2018, the Company accepted an assignment of the property in-lieu of repayment of the loan, and marked the assets received and liabilities assumed to fair value, which exceeded the carrying value of the loan. (12) This loan was extended in March 2018. (13) This loan was extended in April 2018. (14) This loan was repaid in February 2018. (15) This loan was sold in May 2018. Preferred Equity Investments As of June 30, 2018 and December 31, 2017 , we held the following preferred equity investments with an aggregate weighted average current yield of 5.73% at June 30, 2018 (in thousands): Type June 30, 2018 June 30, 2018 Senior June 30, 2018 (1) December 31, 2017 (1) Maturity (2) Preferred Equity $ — $ 272,000 $ 145,132 $ 144,423 April 2021 Total $ — $ 272,000 $ 145,132 $ 144,423 (1) Carrying value is net of deferred origination fees. (2) Represents contractual maturity, excluding any unexercised extension options. At June 30, 2018 , all debt and preferred equity investments were performing in accordance with the terms of the relevant investments, with the exception of a junior mortgage participation acquired in September 2014, which was acquired for zero and has a carrying value of zero , as discussed in subnote 3 of the Debt Investments table above, and a mezzanine loan for which the June 2018 interest payment was outstanding as of June 30, 2018 and was subsequently received in July 2018, as discussed in subnote 5 of the Debt Investments table above. 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 and has a carrying value of zero, as discussed in subnote 3 of the Debt Investments table above. We have determined that we have one portfolio segment of financing receivables at June 30, 2018 and December 31, 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 $89.6 million and $65.5 million at June 30, 2018 and December 31, 2017 , respectively. No financing receivables were 90 days past due at June 30, 2018 .

Investments in Unconsolidated J

Investments in Unconsolidated Joint Ventures	6 Months Ended
	Jun. 30, 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 June 30, 2018 and December 31, 2017 , 800 Third Avenue, 21 East 66th Street, 605 West 42 nd 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 $ 680.1 million and $606.2 million as of June 30, 2018 and December 31, 2017 , respectively. 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 June 30, 2018 : Property Partner Ownership (1) Economic (1) Unaudited Approximate Square Feet Acquisition Date (2) Acquisition (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/ 30.00% 30.00% 17,150 December 2010 10,800 3 Columbus Circle (4) The Moinian Group 48.90% 48.90% 741,500 January 2011 500,000 280 Park Avenue Vornado Realty Trust 50.00% 50.00% 1,219,158 March 2011 400,000 1552-1560 Broadway (5) Jeff Sutton 50.00% 50.00% 57,718 August 2011 136,550 724 Fifth Avenue (6) Jeff Sutton 50.00% 50.00% 65,010 January 2012 223,000 10 East 53rd Street Canadian Pension Plan Investment Board 55.00% 55.00% 354,300 February 2012 252,500 521 Fifth Avenue Plaza Global 50.50% 50.50% 460,000 November 2012 315,000 21 East 66th Street (7) Private Investors 32.28% 32.28% 13,069 December 2012 75,000 650 Fifth Avenue (8) 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 (9) Various Various Various 1,439,016 February 2015 36,668 131-137 Spring Street Invesco Real Estate 20.00% 20.00% 68,342 August 2015 277,750 605 West 42nd Street The Moinian Group 20.00% 20.00% 927,358 April 2016 759,000 11 Madison Avenue PGIM Real Estate 60.00% 60.00% 2,314,000 August 2016 2,605,000 333 East 22nd Street Private Investors 33.33% 33.33% 26,926 August 2016 — 400 East 57th Street (10) BlackRock, Inc and Stonehenge Partners 51.00% 41.00% 290,482 October 2016 170,000 One Vanderbilt (11) National Pension Service of Korea/Hines Interest LP 71.01% 71.01% — January 2017 3,310,000 Mezzanine Loan (12) Private Investors 33.33% 33.33% — May 2017 15,000 Worldwide Plaza RXR Realty / New York REIT / Private Investor 24.35% 24.35% 2,048,725 October 2017 1,725,000 1515 Broadway (13) Allianz Real Estate of America 56.87% 56.87% 1,750,000 November 2017 1,950,000 (1) Ownership interest and economic interest represent the Company's interests in the joint venture as of June 30, 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) As a result of the sale of a condominium interest in September 2012, Young & Rubicam, Inc., or Y&R, owns floors three through eight at the property. Because the joint venture has an option to repurchase these floors, the gain associated with this sale was deferred. (5) The purchase price represents only the purchase of the 1552 Broadway interest which comprised approximately 13,045 square feet. The joint venture also owns a long-term leasehold interest in the retail space and certain other spaces at 1560 Broadway, which is adjacent to 1552 Broadway. (6) In July 2018, the Company closed on the sale of substantially all of its interest in 724 Fifth Avenue to its joint venture partner. (7) 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. (8) 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. (9) 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. (10) 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. (11) The partners have committed aggregate equity 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 June 30, 2018 the total of the two partners' ownership interests based on equity contributed was 13.39% . (12) In May 2017, the Company contributed a mezzanine loan secured by a commercial property in midtown Manhattan to a joint venture and retained a 33.33% interest in the venture. The carrying value is net of $10.0 million that was sold, which is included in other assets and other liabilities on the consolidated balance sheets as a result of the transfers not meeting the conditions for sale accounting. The loan was repaid in August 2018. (13) 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 June 30, 2018 and December 31, 2017, the carrying value for acquisition, development and construction arrangements were as follows (in thousands): Loan Type June 30, 2018 December 31, 2017 Maturity Date Preferred Equity $ 141,000 $ — September 2018 Mezzanine Loan (1) 44,483 44,823 February 2022 Mezzanine Loan (2) 28,105 26,716 July 2036 Mezzanine Loan and Preferred Equity (3) — 100,000 $ 213,588 $ 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 Company was redeemed on this investment in July 2018. (3) The mezzanine loan was repaid and the preferred equity interest was redeemed in March 2018. Sale of Joint Venture Interests or Properties The following table summarizes the investments in unconsolidated joint ventures sold during the six months ended June 30, 2018 : Property Ownership Interest Disposition Date Type of Sale Gross Asset Valuation (in thousands) (1) Gain (Loss) on Sale (in thousands) (2) 1274 Fifth Avenue (3) 9.83% February 2018 Property $ 44,100 $ (362 ) 1515 Broadway (4) 13.00% February 2018 Ownership Interest 1,950,000 — Stonehenge Village (3) 5.00% March 2018 Property 287,000 (5,701 ) 175-225 Third Street Brooklyn, New York 95.00% April 2018 Property 115,000 19,483 1745 Broadway 56.87% May 2018 Property 633,000 52,038 Jericho Plaza 11.67% June 2018 Ownership Interest 117,400 147 (1) Represents implied gross valuation for the joint venture or sales price of the property. (2) Represents the Company's share of the gain (loss). (3) Property was part of the Stonehenge Portfolio. (4) Our investment in 1515 Broadway was marked to fair value on January 1, 2018 upon adoption of ASC 610-20. Joint Venture Mortgages and Other Loans Payable We generally finance our joint ventures with non-recourse debt. In certain cases we have provided guarantees or master leases for tenant space, which terminate upon the satisfaction of specified circumstances or repayment of the underlying loans. The first mortgage notes and other loans payable collateralized by the respective joint venture properties and assignment of leases at June 30, 2018 and December 31, 2017 , respectively, are as follows (amounts in thousands): Property Economic (1) Maturity Date Interest Rate (2) June 30, 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 — 3 Columbus Circle 48.90 % March 2025 3.61 % 350,000 350,000 1515 Broadway 56.87 % March 2025 3.93 % 864,238 872,528 11 Madison Avenue 60.00 % September 2025 3.84 % 1,400,000 1,400,000 800 Third Avenue 60.52 % February 2026 3.37 % 177,000 177,000 400 East 57th Street 41.00 % November 2026 3.00 % 100,000 100,000 Worldwide Plaza 24.35 % November 2027 3.98 % 1,200,000 1,200,000 Stonehenge Portfolio (5) Various Various 4.20 % 323,058 357,282 Total fixed rate debt $ 6,026,624 $ 5,569,138 Floating Rate Debt: 724 Fifth Avenue (6) 50.00 % April 2019 L+ 2.42 % $ 275,000 $ 275,000 280 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 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 (7) 25.00 % November 2020 L+ 2.13 % 174,430 171,444 11 West 34th Street 30.00 % January 2021 L+ 1.45 % 23,000 23,000 100 Park Avenue 49.90 % February 2021 L+ 1.75 % 360,000 360,000 One Vanderbilt (8) 71.01 % September 2021 L+ 3.50 % 375,000 355,535 605 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 % 1,608 1,648 Stonehenge Portfolio Various January 2021 L+ 1.40 % 38,000 55,340 175-225 Third Street (9) — 40,000 1745 Broadway (10) — 345,000 Jericho Plaza (11) — 81,099 Total floating rate debt $ 3,518,038 $ 3,979,066 Total joint venture mortgages and other loans payable $ 9,544,662 $ 9,548,204 Deferred financing costs, net (110,924 ) (136,103 ) Total joint venture mortgages and other loans payable, net $ 9,433,738 $ 9,412,101 (1) Economic interest represents the Company's interests in the joint venture as of June 30, 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 rates as of June 30, 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 $135.7 million , $54.8 million , and $132.6 million in fixed-rate mortgages that mature in August 2019, June 2024, and April 2028, respectively. (6) In July 2018, the Company closed on the sale of substantially all of its interest in 724 Fifth Avenue to its joint venture partner. (7) This loan has a committed amount of $195.0 million , of which $20.6 million was unfunded as of June 30, 2018 . (8) This loan is a $1.5 billion construction facility, which bears interest at 350 basis points over 30-day LIBOR, 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. (9) In April 2018, along with our joint venture partner, we closed on the sale of the property. (10) In May 2018, along with our joint venture partner, we closed on the sale of the property. (11) In June 2018, we closed on the sale of our interest in the property. 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, 3 Columbus Circle, 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 $3.0 million and $6.9 million from these services, net of our ownership share of the joint ventures, for the three and six months ended June 30, 2018 , respectively. We earned $12.4 million and $17.9 million from these services, net of our ownership share of the joint ventures, for the three and six months ended June 30, 2017 , 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 June 30, 2018 and December 31, 2017 are as follows (in thousands): June 30, 2018 December 31, 2017 Assets (1) Commercial real estate property, net $ 14,193,325 $ 12,822,133 Cash and restricted cash 434,307 494,909 Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance 308,653 349,944 Debt and preferred equity investments, net 228,588 202,539 Other assets 2,254,990 1,407,806 Total assets $ 17,419,863 $ 15,277,331 Liabilities and equity (1) Mortgages and other loans payable, net $ 9,433,738 $ 9,412,101 Deferred revenue/gain 1,863,384 985,648 Other liabilities 478,916 411,053 Equity 5,643,825 4,468,529 Total liabilities and equity $ 17,419,863 $ 15,277,331 Company's investments in unconsolidated joint ventures $ 3,059,985 $ 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, for the three and six months ended June 30, 2018 and 2017 , are as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Total revenues $ 314,195 $ 210,590 $ 635,136 $ 427,109 Operating expenses 50,356 39,147 110,129 77,941 Ground rent 4,457 4,179 8,850 8,430 Real estate taxes 55,838 35,170 112,865 70,109 Interest expense, net of interest income 91,648 59,702 181,389 115,030 Amortization of deferred financing costs 7,350 7,458 12,466 13,963 Transaction related costs — 56 — 146 Depreciation and amortization 111,495 65,944 216,575 137,109 Total expenses 321,144 211,656 642,274 422,728 Net (loss) income before gain on sale (1) $ (6,949 ) $ (1,066 ) $ (7,138 ) $ 4,381 Company's equity in net income from unconsolidated joint ventures (1) $ 4,702 $ 3,412 $ 8,738 $ 10,026 (1) The combined statements of operation 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	6 Months Ended
	Jun. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred Costs	Deferred Costs Deferred costs at June 30, 2018 and December 31, 2017 consisted of the following (in thousands): June 30, 2018 December 31, 2017 Deferred leasing costs $ 426,875 $ 443,341 Less: accumulated amortization (227,934 ) (217,140 ) Deferred costs, net $ 198,941 $ 226,201

Mortgages and Other Loans Payab

Mortgages and Other Loans Payable	6 Months Ended
	Jun. 30, 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 June 30, 2018 and December 31, 2017 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) June 30, 2018 December 31, 2017 Fixed Rate Debt: One Madison Avenue May 2020 5.91 % $ 469,564 $ 486,153 762 Madison Avenue February 2022 5.00 % 771 771 100 Church Street July 2022 4.68 % 215,223 217,273 420 Lexington Avenue October 2024 3.99 % 300,000 300,000 400 East 58th Street (2) November 2026 3.00 % 40,000 40,000 Landmark Square January 2027 4.90 % 100,000 100,000 485 Lexington Avenue February 2027 4.25 % 450,000 450,000 1080 Amsterdam (3) February 2027 3.58 % 36,138 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 Total fixed rate debt $ 1,861,696 $ 2,400,560 Floating Rate Debt: 719 Seventh Avenue February 2019 L+ 3.05 % $ 44,000 $ 41,622 183, 187 Broadway & 5-7 Dey Street (7) May 2019 L+ 2.70 % 58,000 58,000 2017 Master Repurchase Agreement (8) June 2019 L+ 2.34 % 300,000 90,809 220 East 42nd Street October 2020 L+ 1.60 % 275,000 275,000 Total floating rate debt $ 677,000 $ 465,431 Total fixed rate and floating rate debt $ 2,538,696 $ 2,865,991 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 2,538,696 $ 2,865,991 Deferred financing costs, net of amortization (21,599 ) (28,709 ) Total mortgages and other loans payable, net $ 2,517,097 $ 2,837,282 (1) Interest rate as of June 30, 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 property. (6) In June 2018, the Series J Preferred Units were redeemed in connection with the sale of the property. (7) In May 2018, we exercised a 12 -month extension option. (8) In June 2018, we exercised a 12 -month extension option. At June 30, 2018 and December 31, 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 $3.8 billion and $4.8 billion , 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 June 30, 2018 , the facility had an outstanding balance of $299.2 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 June 30, 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 June 30, 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 June 30, 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 June 30, 2018 , the facility fee was 20 basis points. As of June 30, 2018 , we had $11.8 million of outstanding letters of credit, $360.0 million drawn under the revolving credit facility and $1.5 billion outstanding under the term loan facilities, with total undrawn capacity of $1.1 billion under the 2017 credit facility. At June 30, 2018 and December 31, 2017 , the revolving credit facility had a carrying value of $351.3 million and $30.3 million , respectively, net of deferred financing costs. At June 30, 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. ROP is a guarantor under the 2017 credit facility. The 2017 credit facility includes certain restrictions and covenants (see Restrictive Covenants below). Senior Unsecured Notes The following table sets forth our senior unsecured notes and other related disclosures as of June 30, 2018 and December 31, 2017 , respectively, by scheduled maturity date (amounts in thousands): Issuance June 30, June 30, December 31, Coupon Rate (1) Initial Term (in Years) Maturity Date August 5, 2011 (2) $ 250,000 $ 249,991 $ 249,953 5.00 % 7 August 2018 March 16, 2010 (2) 250,000 250,000 250,000 7.75 % 10 March 2020 October 5, 2017 (3) 500,000 499,539 499,489 3.25 % 5 October 2022 November 15, 2012 (4) 300,000 304,673 305,163 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 $ 1,400,000 $ 1,404,203 $ 1,404,605 Deferred financing costs, net (7,481 ) (8,666 ) $ 1,400,000 $ 1,396,722 $ 1,395,939 (1) Interest on the senior unsecured notes is payable semi-annually with principal and unpaid interest due on the scheduled maturity dates. (2) Issued by the Company, the Operating Partnership and ROP, as co-obligors. (3) Issued by the Operating Partnership with the Company and ROP as guarantors. (4) In October 2017, the Company, the Operating Partnership and ROP, as co-obligors, issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022. The notes were priced at 105.334% . In August 2018, the Operating Partnership issued $350.0 million of senior unsecured notes, with the Company and ROP as guarantors. The notes bear interest at a floating rate, reset quarterly, equal to three-month LIBOR plus 98 basis points. The notes will mature in August 2021 and can be redeemed at par beginning in August 2019. 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 June 30, 2018 and December 31, 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 June 30, 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 Remaining 2018 $ 19,097 $ — $ — $ — $ — $ 250,000 $ 269,097 $ 4,986 2019 42,271 102,000 — — — — 144,271 252,795 2020 23,466 979,531 — — — 250,000 1,252,997 276,006 2021 11,638 — — — — — 11,638 454,621 2022 9,430 198,555 — — — 800,000 1,007,985 220,810 Thereafter 16,591 1,136,117 360,000 1,500,000 100,000 100,000 3,212,708 2,879,344 $ 122,493 $ 2,416,203 $ 360,000 $ 1,500,000 $ 100,000 $ 1,400,000 $ 5,898,696 $ 4,088,562 Consolidated interest expense, excluding capitalized interest, was comprised of the following (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Interest expense before capitalized interest $ 61,553 $ 71,992 $ 116,471 $ 144,414 Interest capitalized (7,594 ) (6,743 ) (14,280 ) (13,022 ) Interest income (348 ) (393 ) (664 ) (914 ) Interest expense, net $ 53,611 $ 64,856 $ 101,527 $ 130,478

Corporate Indebtedness

Corporate Indebtedness	6 Months Ended
	Jun. 30, 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 June 30, 2018 and December 31, 2017 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) June 30, 2018 December 31, 2017 Fixed Rate Debt: One Madison Avenue May 2020 5.91 % $ 469,564 $ 486,153 762 Madison Avenue February 2022 5.00 % 771 771 100 Church Street July 2022 4.68 % 215,223 217,273 420 Lexington Avenue October 2024 3.99 % 300,000 300,000 400 East 58th Street (2) November 2026 3.00 % 40,000 40,000 Landmark Square January 2027 4.90 % 100,000 100,000 485 Lexington Avenue February 2027 4.25 % 450,000 450,000 1080 Amsterdam (3) February 2027 3.58 % 36,138 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 Total fixed rate debt $ 1,861,696 $ 2,400,560 Floating Rate Debt: 719 Seventh Avenue February 2019 L+ 3.05 % $ 44,000 $ 41,622 183, 187 Broadway & 5-7 Dey Street (7) May 2019 L+ 2.70 % 58,000 58,000 2017 Master Repurchase Agreement (8) June 2019 L+ 2.34 % 300,000 90,809 220 East 42nd Street October 2020 L+ 1.60 % 275,000 275,000 Total floating rate debt $ 677,000 $ 465,431 Total fixed rate and floating rate debt $ 2,538,696 $ 2,865,991 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 2,538,696 $ 2,865,991 Deferred financing costs, net of amortization (21,599 ) (28,709 ) Total mortgages and other loans payable, net $ 2,517,097 $ 2,837,282 (1) Interest rate as of June 30, 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 property. (6) In June 2018, the Series J Preferred Units were redeemed in connection with the sale of the property. (7) In May 2018, we exercised a 12 -month extension option. (8) In June 2018, we exercised a 12 -month extension option. At June 30, 2018 and December 31, 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 $3.8 billion and $4.8 billion , 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 June 30, 2018 , the facility had an outstanding balance of $299.2 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 June 30, 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 June 30, 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 June 30, 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 June 30, 2018 , the facility fee was 20 basis points. As of June 30, 2018 , we had $11.8 million of outstanding letters of credit, $360.0 million drawn under the revolving credit facility and $1.5 billion outstanding under the term loan facilities, with total undrawn capacity of $1.1 billion under the 2017 credit facility. At June 30, 2018 and December 31, 2017 , the revolving credit facility had a carrying value of $351.3 million and $30.3 million , respectively, net of deferred financing costs. At June 30, 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. ROP is a guarantor under the 2017 credit facility. The 2017 credit facility includes certain restrictions and covenants (see Restrictive Covenants below). Senior Unsecured Notes The following table sets forth our senior unsecured notes and other related disclosures as of June 30, 2018 and December 31, 2017 , respectively, by scheduled maturity date (amounts in thousands): Issuance June 30, June 30, December 31, Coupon Rate (1) Initial Term (in Years) Maturity Date August 5, 2011 (2) $ 250,000 $ 249,991 $ 249,953 5.00 % 7 August 2018 March 16, 2010 (2) 250,000 250,000 250,000 7.75 % 10 March 2020 October 5, 2017 (3) 500,000 499,539 499,489 3.25 % 5 October 2022 November 15, 2012 (4) 300,000 304,673 305,163 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 $ 1,400,000 $ 1,404,203 $ 1,404,605 Deferred financing costs, net (7,481 ) (8,666 ) $ 1,400,000 $ 1,396,722 $ 1,395,939 (1) Interest on the senior unsecured notes is payable semi-annually with principal and unpaid interest due on the scheduled maturity dates. (2) Issued by the Company, the Operating Partnership and ROP, as co-obligors. (3) Issued by the Operating Partnership with the Company and ROP as guarantors. (4) In October 2017, the Company, the Operating Partnership and ROP, as co-obligors, issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022. The notes were priced at 105.334% . In August 2018, the Operating Partnership issued $350.0 million of senior unsecured notes, with the Company and ROP as guarantors. The notes bear interest at a floating rate, reset quarterly, equal to three-month LIBOR plus 98 basis points. The notes will mature in August 2021 and can be redeemed at par beginning in August 2019. 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 June 30, 2018 and December 31, 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 June 30, 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 Remaining 2018 $ 19,097 $ — $ — $ — $ — $ 250,000 $ 269,097 $ 4,986 2019 42,271 102,000 — — — — 144,271 252,795 2020 23,466 979,531 — — — 250,000 1,252,997 276,006 2021 11,638 — — — — — 11,638 454,621 2022 9,430 198,555 — — — 800,000 1,007,985 220,810 Thereafter 16,591 1,136,117 360,000 1,500,000 100,000 100,000 3,212,708 2,879,344 $ 122,493 $ 2,416,203 $ 360,000 $ 1,500,000 $ 100,000 $ 1,400,000 $ 5,898,696 $ 4,088,562 Consolidated interest expense, excluding capitalized interest, was comprised of the following (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Interest expense before capitalized interest $ 61,553 $ 71,992 $ 116,471 $ 144,414 Interest capitalized (7,594 ) (6,743 ) (14,280 ) (13,022 ) Interest income (348 ) (393 ) (664 ) (914 ) Interest expense, net $ 53,611 $ 64,856 $ 101,527 $ 130,478

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 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, the chairman of our board of directors, and provide services to certain properties owned by us. Alliance’s affiliates include First Quality Maintenance, L.P., or First Quality, Classic Security LLC, Bright Star Couriers LLC and Onyx Restoration Works, and provide cleaning, extermination, security, messenger, and restoration services, respectively. In addition, First Quality has the non-exclusive opportunity to provide cleaning and related services to individual tenants at our properties on a basis separately negotiated with any tenant seeking such additional services. The Service Corporation has entered into an arrangement with Alliance whereby it will receive a profit participation above a certain threshold for services provided by Alliance to certain tenants at certain buildings above the base services specified in their lease agreements. Income earned from the profit participation, which is included in other income on the consolidated statements of operations, was $1.0 million and $2.0 million for the three and six months ended June 30, 2018 , respectively, and was $1.0 million and $2.0 million for the three and six months ended June 30, 2017 , respectively. We also recorded expenses, inclusive of capitalized expenses, of $5.1 million and $9.1 million for the three and six months ended June 30, 2018 , respectively, for these services (excluding services provided directly to tenants), and $5.8 million and $10.3 million for the three and six months ended June 30, 2017 , respectively. 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 $0.1 million and $0.3 million for the three and six months ended June 30, 2018 , respectively and $0.1 million and $0.3 million for the three and six months ended June 30, 2017 , 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. 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 June 30, 2018 and December 31, 2017 consisted of the following (in thousands): June 30, 2018 December 31, 2017 Due from joint ventures $ 17,446 $ 15,025 Other 10,408 8,014 Related party receivables $ 27,854 $ 23,039

Noncontrolling Interests on the

Noncontrolling Interests on the Company's Consolidated Financial Statements	6 Months Ended
	Jun. 30, 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 June 30, 2018 and December 31, 2017 , the noncontrolling interest unit holders owned 5.20% , or 4,699,872 units, and 4.58% , or 4,452,979 units, of the Operating Partnership, respectively. As of June 30, 2018 , 4,699,872 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 for the six months ended June 30, 2018 and the twelve months ended December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Balance at beginning of period $ 461,954 $ 473,882 Distributions (7,712 ) (14,266 ) Issuance of common units 17,714 25,723 Redemption of common units (1,561 ) (21,574 ) Net income 10,858 3,995 Accumulated other comprehensive income allocation 864 (94 ) Fair value adjustment 4,493 (5,712 ) Balance at end of period $ 486,610 $ 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 June 30, 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 for the three months ended June 30, 2018 and the twelve months ended December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Balance at beginning of period $ 301,735 $ 302,010 Issuance of preferred units — — Redemption of preferred units (350 ) (275 ) Balance at end of period $ 301,385 $ 301,735

Stockholders' Equity of the Com

Stockholders' Equity of the Company	6 Months Ended
	Jun. 30, 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 June 30, 2018 , 85,725,135 shares of common stock and no shares of excess stock were issued and outstanding. Stock Repurchase Program In August 2016, our Board of Directors approved a stock repurchase plan under which we can repurchase up to $1.0 billion of shares of our common stock. The Board of Directors has since authorized two separate $500.0 million increases to the size of the share repurchase program in the fourth quarter of 2017 and the second quarter of 2018 bringing the program total to $2.0 billion . At June 30, 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 Maximum approximate dollar value of shares that may yet be repurchased under the plan (in millions) (1) 2017 8,342,411 $101.64 8,342,411 $1,152.0 First quarter 2018 3,653,928 $97.07 11,996,339 $797.2 Second quarter 2018 (2) 3,479,552 $97.22 15,475,891 $458.9 (1) Reflective of $2.0 billion plan maximum as of June 30, 2018 . (2) Includes 101,421 shares of common stock repurchased by the Company in June 2018 that were settled in July 2018. 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 six months ended June 30, 2018 and 2017 , respectively (dollars in thousands): Six Months Ended June 30, 2018 2017 Shares of common stock issued 674 1,036 Dividend reinvestments/stock purchases under the DRSPP $ 64 $ 111 Earnings per Share SL Green's earnings per share for the three and six months ended June 30, 2018 and 2017 are computed as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, Numerator 2018 2017 2018 2017 Basic Earnings: Income attributable to SL Green common stockholders $ 103,556 $ 8,222 $ 205,322 $ 19,573 Effect of Dilutive Securities: Redemption of units to common shares 5,586 419 10,858 895 Diluted Earnings: Income attributable to SL Green common stockholders $ 109,142 $ 8,641 $ 216,180 $ 20,468 Three Months Ended June 30, Six Months Ended June 30, Denominator 2018 2017 2018 2017 Basic Shares: Weighted average common stock outstanding 87,176 99,900 88,772 100,268 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,706 4,562 4,695 4,584 Stock-based compensation plans 201 270 200 288 Diluted weighted average common stock outstanding 92,083 104,732 93,667 105,140 SL Green has excluded 1,158,317 and 1,184,735 common stock equivalents from the diluted shares outstanding for the three and six months ended June 30, 2018 , respectively, as they were anti-dilutive. SL Green has excluded 986,390 and 979,676 common stock equivalents from the diluted shares outstanding for the three and six months ended June 30, 2017 , respectively, as they were anti-dilutive. Accumulated Other Comprehensive Income The following tables set forth the changes in accumulated other comprehensive income (loss) by component as of June 30, 2018 (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, 2017 $ 12,542 $ 5,020 $ 1,042 $ 18,604 Other comprehensive (loss) income before reclassifications 9,837 4,097 (14 ) 13,920 Amounts reclassified from accumulated other comprehensive income 237 (139 ) — 98 Balance at June 30, 2018 $ 22,616 $ 8,978 $ 1,028 $ 32,622 (1) Amount reclassified from accumulated other comprehensive income (loss) is included in interest expense in the respective consolidated statements of operations. As of June 30, 2018 and December 31, 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 $2.2 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.

Partners' Capital of the Operat

Partners' Capital of the Operating Partnership	6 Months Ended
	Jun. 30, 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 June 30, 2018 , 85,725,135 shares of common stock and no shares of excess stock were issued and outstanding. Stock Repurchase Program In August 2016, our Board of Directors approved a stock repurchase plan under which we can repurchase up to $1.0 billion of shares of our common stock. The Board of Directors has since authorized two separate $500.0 million increases to the size of the share repurchase program in the fourth quarter of 2017 and the second quarter of 2018 bringing the program total to $2.0 billion . At June 30, 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 Maximum approximate dollar value of shares that may yet be repurchased under the plan (in millions) (1) 2017 8,342,411 $101.64 8,342,411 $1,152.0 First quarter 2018 3,653,928 $97.07 11,996,339 $797.2 Second quarter 2018 (2) 3,479,552 $97.22 15,475,891 $458.9 (1) Reflective of $2.0 billion plan maximum as of June 30, 2018 . (2) Includes 101,421 shares of common stock repurchased by the Company in June 2018 that were settled in July 2018. 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 six months ended June 30, 2018 and 2017 , respectively (dollars in thousands): Six Months Ended June 30, 2018 2017 Shares of common stock issued 674 1,036 Dividend reinvestments/stock purchases under the DRSPP $ 64 $ 111 Earnings per Share SL Green's earnings per share for the three and six months ended June 30, 2018 and 2017 are computed as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, Numerator 2018 2017 2018 2017 Basic Earnings: Income attributable to SL Green common stockholders $ 103,556 $ 8,222 $ 205,322 $ 19,573 Effect of Dilutive Securities: Redemption of units to common shares 5,586 419 10,858 895 Diluted Earnings: Income attributable to SL Green common stockholders $ 109,142 $ 8,641 $ 216,180 $ 20,468 Three Months Ended June 30, Six Months Ended June 30, Denominator 2018 2017 2018 2017 Basic Shares: Weighted average common stock outstanding 87,176 99,900 88,772 100,268 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,706 4,562 4,695 4,584 Stock-based compensation plans 201 270 200 288 Diluted weighted average common stock outstanding 92,083 104,732 93,667 105,140 SL Green has excluded 1,158,317 and 1,184,735 common stock equivalents from the diluted shares outstanding for the three and six months ended June 30, 2018 , respectively, as they were anti-dilutive. SL Green has excluded 986,390 and 979,676 common stock equivalents from the diluted shares outstanding for the three and six months ended June 30, 2017 , respectively, as they were anti-dilutive. Accumulated Other Comprehensive Income The following tables set forth the changes in accumulated other comprehensive income (loss) by component as of June 30, 2018 (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, 2017 $ 12,542 $ 5,020 $ 1,042 $ 18,604 Other comprehensive (loss) income before reclassifications 9,837 4,097 (14 ) 13,920 Amounts reclassified from accumulated other comprehensive income 237 (139 ) — 98 Balance at June 30, 2018 $ 22,616 $ 8,978 $ 1,028 $ 32,622 (1) Amount reclassified from accumulated other comprehensive income (loss) is included in interest expense in the respective consolidated statements of operations. As of June 30, 2018 and December 31, 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 $2.2 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.
SL Green Operating Partnership
Stockholders' Equity
Partners' Capital of the Operating Partnership	Partners' Capital of the Operating Partnership The Company is the sole general partner of the Operating Partnership and at June 30, 2018 owned 85,725,135 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 June 30, 2018 , limited partners other than SL Green owned 5.20% , or 4,699,872 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 three and six months ended June 30, 2018 and 2017 , respectively, are computed as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, Numerator 2018 2017 2018 2017 Basic and Diluted Earnings: Income attributable to SLGOP common unitholders $ 109,142 $ 8,641 $ 216,180 $ 20,468 Three Months Ended June 30, Six Months Ended June 30, Denominator 2018 2017 2018 2017 Basic units: Weighted average common units outstanding 91,882 104,462 93,467 104,852 Effect of Dilutive Securities: Stock-based compensation plans 201 270 200 288 Diluted weighted average common units outstanding 92,083 104,732 93,667 105,140 The Operating Partnership has excluded 1,158,317 and 1,184,735 common unit equivalents from the diluted units outstanding for the three and six months ended June 30, 2018 , respectively, as they were anti-dilutive. The Operating Partnership has excluded 986,390 and 979,676 common unit equivalents from the diluted units outstanding for the three and six months ended June 30, 2017 , respectively, as they were anti-dilutive.

Share-based Compensation

Share-based Compensation	6 Months Ended
	Jun. 30, 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 June 30, 2018 , 7.4 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 six months ended June 30, 2018 and the year ended December 31, 2017 . June 30, 2018 December 31, 2017 Dividend yield 2.85 % 2.51 % Expected life 3.5 years 4.4 years Risk-free interest rate 2.48 % 1.73 % Expected stock price volatility 22.00 % 28.10 % A summary of the status of the Company's stock options as of June 30, 2018 and December 31, 2017 , and changes during the six months ended June 30, 2018 and year ended December 31, 2017 are as follows: June 30, 2018 December 31, 2017 Options Outstanding Weighted Average Exercise Price Options Outstanding Weighted Average Exercise Price Balance at beginning of period 1,548,719 $ 101.48 1,737,213 $ 98.44 Granted 6,000 97.91 174,000 105.66 Exercised (58,734 ) 89.62 (292,193 ) 81.07 Lapsed or canceled (56,033 ) 114.70 (70,301 ) 121.68 Balance at end of period 1,439,952 $ 101.43 1,548,719 $ 101.48 Options exercisable at end of period 1,067,969 $ 98.93 800,902 $ 94.33 Total fair value of options granted during the period $ 84,068 $ 3,816,652 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 3.2 years and the remaining average contractual life of the options exercisable was 3.2 years. During the three and six months ended June 30, 2018 , we recognized compensation expense for these options of $1.6 million and $3.2 million , respectively. During the three and six months ended June 30, 2017 , we recognized compensation expense for these options of $1.9 million and $3.9 million , respectively. As of June 30, 2018 , there was $4.9 million of total unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted average period of 1.3 years. Stock-based Compensation Effective January 1, 1999, the Company implemented a deferred compensation plan, or the Deferred Plan, where shares issued under the Deferred Plan were granted to certain employees, including our executives and vesting will occur annually upon the completion of a service period or our meeting established financial performance criteria. Annual vesting occurs at rates ranging from 15% to 35% once performance criteria are reached. A summary of the Company's restricted stock as of June 30, 2018 and December 31, 2017 and charges during the six months ended June 30, 2018 and the year ended December 31, 2017 , are as follows: June 30, 2018 December 31, 2017 Balance at beginning of period 3,298,216 3,202,031 Granted 1,700 96,185 Canceled (8,300 ) — Balance at end of period 3,291,616 3,298,216 Vested during the period 92,114 95,736 Compensation expense recorded $ 6,251,350 $ 9,809,749 Total fair value of restricted stock granted during the period $ 163,831 $ 9,905,986 The fair value of restricted stock that vested during the six months ended June 30, 2018 and the year ended December 31, 2017 was $9.8 million and $9.4 million , respectively. As of June 30, 2018 there was $15.2 million of total unrecognized compensation cost related to restricted stock, which is expected to be recognized over a weighted average period of 1.8 years . For the three and six months ended June 30, 2018 , $1.6 million and $3.2 million , respectively, was capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options. For the three and six months ended June 30, 2017 $2.0 million and $3.6 million , respectively, was capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options. We granted LTIP Units, which include bonus, time-based and performance based awards, with a fair value of $20.6 million and $20.5 million as of June 30, 2018 and December 31, 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 June 30, 2018 , there was $7.5 million of total unrecognized compensation expense related to the time-based and performance based awards, which is expected to be recognized over a weighted average period of 1.1 years . During the three and six months ended June 30, 2018 , we recorded compensation expense related to bonus, time-based and performance based awards of $2.3 million and $9.1 million , respectively. During the three and six months ended June 30, 2017 we recorded compensation expense related to bonus, time-based and performance based awards of $2.6 million and $12.6 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 no compensation expense for the three and six months ended June 30, 2018 related to the 2014 Outperformance Plan. We recorded compensation expense of $4.3 million and $6.3 million for the three and six months ended June 30, 2017 , 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 six months ended June 30, 2018 , 11,502 phantom stock units and 9,332 shares of common stock were issued to our board of directors. We recorded compensation expense of $0.1 million and $2.1 million during the three and six months ended June 30, 2018 , respectively, related to the Deferred Compensation Plan. We recorded compensation expense of $0.2 million and $2.1 million during the three and six months ended June 30, 2017 , respectively, related to the Deferred Compensation Plan. As of June 30, 2018 , there were 111,356 phantom stock units outstanding pursuant to our Non-Employee Director's Deferral Program. Employee Stock Purchase Plan In 2007, the Company's board of directors adopted the 2008 Employee Stock Purchase Plan, or ESPP, to encourage our employees to increase their efforts to make our business more successful by providing equity-based incentives to eligible employees. The ESPP is intended to qualify as an "employee stock purchase plan" under Section 423 of the Code, and has been adopted by the board to enable our eligible employees to purchase the Company's shares of common stock through payroll deductions. The ESPP became effective on January 1, 2008 with a maximum of 500,000 shares of the common stock available for issuance, subject to adjustment upon a merger, reorganization, stock split or other similar corporate change. The Company filed a registration statement on Form S-8 with the SEC with respect to the ESPP. The common stock is offered for purchase through a series of successive offering periods. Each offering period will be three months in duration and will begin on the first day of each calendar quarter, with the first offering period having commenced on January 1, 2008. The ESPP provides for eligible employees to purchase the common stock at a purchase price equal to 85% of the lesser of (1) the market value of the common stock on the first day of the offering period or (2) the market value of the common stock on the last day of the offering period. The ESPP was approved by our stockholders at our 2008 annual meeting of stockholders. As of June 30, 2018 , 110,045 shares of our common stock had been issued under the ESPP.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Accumulated Other Comprehensive Income	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 June 30, 2018 , 85,725,135 shares of common stock and no shares of excess stock were issued and outstanding. Stock Repurchase Program In August 2016, our Board of Directors approved a stock repurchase plan under which we can repurchase up to $1.0 billion of shares of our common stock. The Board of Directors has since authorized two separate $500.0 million increases to the size of the share repurchase program in the fourth quarter of 2017 and the second quarter of 2018 bringing the program total to $2.0 billion . At June 30, 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 Maximum approximate dollar value of shares that may yet be repurchased under the plan (in millions) (1) 2017 8,342,411 $101.64 8,342,411 $1,152.0 First quarter 2018 3,653,928 $97.07 11,996,339 $797.2 Second quarter 2018 (2) 3,479,552 $97.22 15,475,891 $458.9 (1) Reflective of $2.0 billion plan maximum as of June 30, 2018 . (2) Includes 101,421 shares of common stock repurchased by the Company in June 2018 that were settled in July 2018. 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 six months ended June 30, 2018 and 2017 , respectively (dollars in thousands): Six Months Ended June 30, 2018 2017 Shares of common stock issued 674 1,036 Dividend reinvestments/stock purchases under the DRSPP $ 64 $ 111 Earnings per Share SL Green's earnings per share for the three and six months ended June 30, 2018 and 2017 are computed as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, Numerator 2018 2017 2018 2017 Basic Earnings: Income attributable to SL Green common stockholders $ 103,556 $ 8,222 $ 205,322 $ 19,573 Effect of Dilutive Securities: Redemption of units to common shares 5,586 419 10,858 895 Diluted Earnings: Income attributable to SL Green common stockholders $ 109,142 $ 8,641 $ 216,180 $ 20,468 Three Months Ended June 30, Six Months Ended June 30, Denominator 2018 2017 2018 2017 Basic Shares: Weighted average common stock outstanding 87,176 99,900 88,772 100,268 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,706 4,562 4,695 4,584 Stock-based compensation plans 201 270 200 288 Diluted weighted average common stock outstanding 92,083 104,732 93,667 105,140 SL Green has excluded 1,158,317 and 1,184,735 common stock equivalents from the diluted shares outstanding for the three and six months ended June 30, 2018 , respectively, as they were anti-dilutive. SL Green has excluded 986,390 and 979,676 common stock equivalents from the diluted shares outstanding for the three and six months ended June 30, 2017 , respectively, as they were anti-dilutive. Accumulated Other Comprehensive Income The following tables set forth the changes in accumulated other comprehensive income (loss) by component as of June 30, 2018 (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, 2017 $ 12,542 $ 5,020 $ 1,042 $ 18,604 Other comprehensive (loss) income before reclassifications 9,837 4,097 (14 ) 13,920 Amounts reclassified from accumulated other comprehensive income 237 (139 ) — 98 Balance at June 30, 2018 $ 22,616 $ 8,978 $ 1,028 $ 32,622 (1) Amount reclassified from accumulated other comprehensive income (loss) is included in interest expense in the respective consolidated statements of operations. As of June 30, 2018 and December 31, 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 $2.2 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	6 Months Ended
	Jun. 30, 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 June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 28,570 $ — $ 28,570 $ — Interest rate cap and swap agreements (included in other assets) $ 26,132 $ — $ 26,132 $ — 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 other than temporary impairment in real estate investments and debt and preferred equity investments, including intangibles primarily utilizing cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as sales comparison approach, which utilizes comparable sales, listings and sales contracts. All of which are classified as Level 3 inputs. 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 $11.1 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 June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Carrying Value (1) Fair Value Carrying Value (1) Fair Value Debt and preferred equity investments $ 2,168,515 (2) $ 2,114,041 (2) Fixed rate debt $ 3,765,899 $ 3,796,225 $ 4,305,165 $ 4,421,866 Variable rate debt 2,137,000 2,151,998 1,605,431 1,612,224 $ 5,902,899 $ 5,948,223 $ 5,910,596 $ 6,034,090 (1) Amounts exclude net deferred financing costs. (2) At June 30, 2018 , debt and preferred equity investments had an estimated fair value ranging between $2.2 billion and $2.4 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 June 30, 2018 and December 31, 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	6 Months Ended
	Jun. 30, 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 June 30, 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 $ 15,272 Interest Rate Swap 100,000 1.161 % July 2016 July 2023 Other Assets 7,496 Interest Rate Cap 137,500 4.000 % September 2017 September 2019 Other Assets 1 Interest Rate Swap 100,000 1.928 % December 2017 November 2020 Other Assets 1,688 Interest Rate Swap 100,000 1.934 % December 2017 November 2020 Other Assets 1,675 $ 26,132 During the three months ended June 30, 2018 , we recorded a loss on the changes in the fair value of $0.1 million , which is included in interest expense in the consolidated statements of operations. During the six months ended June 30, 2018 , we recorded a loss on the changes in the fair value of $0.3 million , which is included in interest expense in the consolidated statements of operations. During the three months ended June 30, 2017 , we did not record a gain or loss on the changes in the fair value. During the six months ended June 30, 2017 , we recorded a loss on the changes in the fair value of $0.1 million , 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 June 30, 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 zero . As of June 30, 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 zero at June 30, 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 $2.6 million of the current balance held in accumulated other comprehensive income will be reclassified into interest expense and $1.4 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 three months ended June 30, 2018 and 2017 , respectively (in thousands): Amount of Gain (Loss) Location of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income Amount of Gain (Loss) Location of Gain (Loss) Recognized in Income on Derivative Amount of Gain (Loss) Three Months Ended June 30, Three Months Ended June 30, Three Months Ended June 30, Derivative 2018 2017 2018 2017 2018 2017 Interest Rate Swaps/Caps $ 3,116 $ (2,036 ) Interest expense $ 76 $ (519 ) Interest expense $ (3 ) $ — Share of unconsolidated joint ventures' derivative instruments 1,092 (1,328 ) Equity in net income from unconsolidated joint ventures 155 (292 ) Equity in net income from unconsolidated joint ventures (30 ) 34 $ 4,208 $ (3,364 ) $ 231 $ (811 ) $ (33 ) $ 34 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 six months ended June 30, 2018 and 2017 , respectively (in thousands): Amount of Gain (Loss) Recognized in Other Comprehensive Loss (Effective Portion) Location of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion) Location of Gain (Loss) Recognized in Income on Derivative Amount of Gain (Loss) Recognized into Income (Ineffective Portion) Six Months Ended June 30, Six Months Ended June 30, Six Months Ended June 30, Derivative 2018 2017 2018 2017 2018 2017 Interest Rate Swaps/Caps $ 10,398 $ (5,173 ) Interest expense $ (253 ) $ (1,498 ) Interest expense $ (12 ) $ (8 ) Share of unconsolidated joint ventures' derivative instruments 4,405 (987 ) Equity in net income from unconsolidated joint ventures 154 (691 ) Equity in net income from unconsolidated joint ventures (119 ) (61 ) $ 14,803 $ (6,160 ) $ (99 ) $ (2,189 ) $ (131 ) $ (69 )

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings As of June 30, 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. Capital and Ground Leases Arrangements 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 June 30, 2018 (in thousands): Capital lease Non-cancellable operating leases Remaining 2018 $ 5,324 $ 17,917 2019 10,826 35,943 2020 11,245 36,435 2021 11,635 36,751 2022 11,856 34,723 2023 12,083 32,548 Thereafter 1,391,127 1,008,718 Total minimum lease payments $ 1,454,096 $ 1,203,035 Amount representing interest (1,145,484 ) Amount classified within liabilities held for sale (1) (265,391 ) Capital lease obligations $ 43,221 (1) Related to the ground lease at 2 Herald Square, which is under contract for sale of a joint venture interest and has been classified as held for sale as of June 30, 2018.

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 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 contribution to income from continuing operations. The primary sources of revenue are generated from tenant rents and escalations and reimbursement revenue. Real estate property operating expenses consist primarily of security, maintenance, utility costs, 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 three and six months ended June 30, 2018 and 2017 , and selected asset information as of June 30, 2018 and December 31, 2017 , regarding our operating segments are as follows (in thousands): Real Estate Segment Debt and Preferred Equity Segment Total Company Total revenues Three months ended: June 30, 2018 $ 251,843 $ 49,273 $ 301,116 June 30, 2017 337,528 60,622 398,150 Six months ended: June 30, 2018 508,248 94,563 602,811 June 30, 2017 674,610 100,921 775,531 Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities Three months ended: June 30, 2018 $ 13,239 $ 34,276 $ 47,515 June 30, 2017 (16,232 ) 52,045 35,813 Six months ended: June 30, 2018 27,263 67,701 94,964 June 30, 2017 (2,425 ) 89,558 87,133 Total assets As of: June 30, 2018 $ 11,249,972 $ 2,463,956 $ 13,713,928 December 31, 2017 11,631,700 2,351,204 13,982,904 Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities represents total revenues less total expenses for the real estate segment and total investment income less allocated interest expense for the debt and preferred equity segment. Interest costs for the debt and preferred equity segment includes actual costs incurred for 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 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 three and six months ended June 30, 2018 , marketing, general and administrative expenses totaled $22.5 million , and $46.0 million , respectively. For the three and six months ended June 30, 2017 , marketing, general and administrative expenses totaled $24.3 million , and $48.4 million , respectively. All other expenses, except interest, relate entirely to the real estate assets. There were no transactions between the above two segments. The table below reconciles net income before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities to net income for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities $ 47,515 $ 35,813 $ 94,964 $ 87,133 Equity in net gain on sale of interest in unconsolidated joint venture/real estate 72,025 13,089 65,585 15,136 Purchase price and other fair value adjustments 11,149 — 60,442 — (Loss) gain on sale of real estate, net (14,790 ) (3,823 ) 8,731 (3,256 ) Depreciable real estate reserves — (29,064 ) — (85,336 ) Gain on sale of investment in marketable securities — — — 3,262 Net income $ 115,899 $ 16,015 $ 229,722 $ 16,939

Significant Accounting Polici31

Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 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 variable interest entity, or VIE, in which we are considered the primary beneficiary. The primary beneficiary is the entity that has (i) the power to direct the activities that most significantly impact the entity's economic performance and (ii) the obligation to absorb losses of the VIE or the right to receive benefits from the VIE that could be significant to the VIE.
Investment in Commercial Real Estate Properties	Investment in Commercial Real Estate Properties 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.
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 other than temporary impairment in real estate investments and debt and preferred equity investments, including intangibles primarily utilizing cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as sales comparison approach, which utilizes comparable sales, listings and sales contracts. All of which are classified as Level 3 inputs. 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 $11.1 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.
Investment in Marketable Securities	Investment in Marketable Securities At acquisition, we designate a debt security as held-to-maturity, available-for-sale, or trading. As of June 30, 2018 , we did not have any debt securities designated as held-to-maturity or trading. We account for our available-for-sale debt securities at fair value pursuant to Accounting Standards Codification, or ASC, 820-10, with the net unrealized gains or losses reported as a component of accumulated other comprehensive income or loss. Any unrealized losses that are determined to be other-than-temporary are recognized in earnings up to their credit component. The 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 June 30, 2018 . The cost of bonds and marketable securities sold is determined using the specific identification method.
Investments in Unconsolidated Joint Ventures	Investments in Unconsolidated Joint Ventures We 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.
Reserve for Possible Credit Losses	Reserve for Possible Credit Losses The reserve for possible credit losses in connection with debt and preferred equity investments is the charge to earnings to increase the allowance for possible credit losses to the level that we estimate to be adequate, based on Level 3 data, considering delinquencies, loss experience and collateral quality. Other factors considered include geographic trends, product diversification, the size of the portfolio and current economic conditions. Based upon these factors, we establish a provision for possible credit loss on each individual investment. When it is probable that we will be unable to collect all amounts contractually due, the investment is considered impaired. Where impairment is indicated on an investment that is held to maturity, a valuation allowance is measured based upon the excess of the recorded investment amount over the fair value of the collateral. Any deficiency between the carrying amount of an asset and the calculated value of the collateral is charged to expense. We continue to assess or adjust our estimates based on circumstances of a loan and the underlying collateral. If additional information reflects increased recovery of our investment, we will adjust our reserves accordingly. There were no loan reserves recorded during the three and six months ended June 30, 2018 and 2017 . Debt and preferred equity investments held for sale are carried at the lower of cost or fair market value using available market information obtained through consultation with dealers or other originators of such investments as well as discounted cash flow models based on Level 3 data pursuant to ASC 820-10. As circumstances change, management may conclude not to sell an investment designated as held for sale. In such situations, the investment will be reclassified at its net carrying value to debt and preferred equity investments held to maturity. For these reclassified investments, the difference between the current carrying value and the expected cash to be collected at maturity will be accreted into income over the remaining term of the investment.
Income Taxes	Income Taxes SL Green is taxed as a REIT under Section 856(c) of the Code. As a REIT, SL Green generally is not subject to Federal income tax. To maintain its qualification as a REIT, SL Green must distribute at least 90% of its REIT taxable income to its stockholders and meet certain other requirements. If SL Green fails to qualify as a REIT in any taxable year, SL Green will be subject to Federal income tax on its taxable income at regular corporate rates. SL Green may also be subject to certain state, local and franchise taxes. Under certain circumstances, Federal income and excise taxes may be due on its undistributed taxable income. The Operating Partnership is a partnership and, as a result, all income and losses of the partnership are allocated to the partners for inclusion in their respective income tax returns. The only provision for income taxes included in the consolidated statements of operations relates to the Operating Partnership’s consolidated taxable REIT subsidiaries. The Operating Partnership may also be subject to certain state, local and franchise taxes. Pursuant to amendments to the Code that became effective January 1, 2001, we have elected, and may elect in the future, to treat certain of our existing or newly created corporate subsidiaries as taxable REIT subsidiaries, or TRSs. In general, TRSs may perform non-customary services for the tenants of the Company, hold assets that we cannot hold directly and generally may engage in any real estate or non-real estate related business. The TRSs generate income, resulting in Federal and state income tax liability for these entities. During the three and six months ended June 30, 2018 , we recorded Federal, state and local tax provisions of $1.1 million and $1.6 million , respectively. 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.
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.
Reclassification	Reclassification Certain prior year balances have been reclassified to conform to our current year presentation.
Accounting Standards Updates	Accounting Standards Updates In June 2018, the FASB issued Accounting Standard Update (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 will be effective for the Company for fiscal years beginning after December 15, 2018, including the interim periods within that fiscal year. 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 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 guidance will be effective for the Company in the interim period beginning after June 15, 2018. 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 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities. The amendments in the new standard will permit more flexibility in hedging interest rate risk for both variable rate and fixed rate financial instruments. The standard will also enhance the presentation of hedge results in the financial statements. The guidance is effective for fiscal years beginning after December 15, 2018. Early adoption is permitted. The Company has not yet adopted the guidance, and does not expect a material impact on the Company’s consolidated financial statements when the new standard is implemented. In May 2017, the FASB issued 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. 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 has not yet adopted this new guidance and is currently evaluating the impact of adopting this new accounting standard on the Company’s consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases, and in July 2018, the FASB issued ASU No. 2018-10, Codification Improvements to Topic 842, Leases and ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. 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 accounting applied by a lessor, inclusive of the effect of a 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 and to adopt, is largely unchanged from that applied under the previous standard. However, 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. The Company is currently quantifying these impacts. This guidance is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early adoption is permitted. The Company expects to adopt this guidance January 1, 2019 and will apply the modified retrospective approach. In January 2016, the FASB issued ASU 2016-01 (Subtopic 825-10), Recognition and Measurement of Financial Assets and Financial Liabilities. The guidance requires entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value through earnings, to record changes in 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 Pre32

Organization and Basis of Presentation (Tables)	6 Months Ended
	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of commercial office properties	As of June 30, 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 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 21 (2) 12,756,091 10 11,491,164 31 24,247,255 94.1 % Retail 4 (3) 302,583 9 347,970 13 650,553 94.2 % Development/Redevelopment 8 318,985 3 416,214 11 735,199 43.9 % Fee Interest — — 1 — 1 — — % 33 13,377,659 23 12,255,348 56 25,633,007 92.6 % Suburban Office 19 (4) 2,835,200 — — 19 2,835,200 87.0 % Retail 1 52,000 — — 1 52,000 100.0 % Development/Redevelopment 1 1,000 — — 1 1,000 — % 21 2,888,200 — — 21 2,888,200 87.2 % Total commercial properties 54 16,265,859 23 12,255,348 77 28,521,207 92.1 % Residential: Manhattan Residential 3 (3) 472,105 10 2,156,751 13 2,628,856 90.0 % Suburban Residential — — — — — — — % Total residential properties 3 472,105 10 2,156,751 13 2,628,856 90.0 % Total portfolio 57 16,737,964 33 14,412,099 90 31,150,063 91.9 % (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) Includes 2 Herald Square, which is under contract for sale of a joint venture interest and has been classified as held for sale as of June 30, 2018 . (3) As of June 30, 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. (4) Includes the properties at 1-6 International Drive in Rye Brook, New York which are classified as held for sale at June 30, 2018 .

Significant Accounting Polici33

Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
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 June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Identified intangible assets (included in other assets): Gross amount $ 263,138 $ 325,880 Accumulated amortization (239,344 ) (277,038 ) Net (1) $ 23,794 $ 48,842 Identified intangible liabilities (included in deferred revenue): Gross amount $ 274,120 $ 540,283 Accumulated amortization (249,905 ) (402,583 ) Net (1) $ 24,215 $ 137,700 (1) As of June 30, 2018 and December 31, 2017, $0.1 million and $13.9 million , respectively and $0.1 million and $4.1 million , respectively, of net intangible assets and net intangible liabilities, were reclassified to assets held for sale and liabilities related to assets held for sale.
Schedule of marketable securities	At June 30, 2018 and December 31, 2017 , we held the following marketable securities (in thousands): June 30, 2018 December 31, 2017 Commercial mortgage-backed securities $ 28,570 $ 28,579 Total marketable securities available-for-sale $ 28,570 $ 28,579

Property Acquisitions (Tables)

Property Acquisitions (Tables)	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition	The following table summarizes the properties acquired during the six months ended June 30, 2018 : Property Acquisition Date Property Type Approximate Square Feet Acquisition Price (in millions) 2 Herald Square (1) May 2018 Leasehold Interest 369,000 $ 266.0 (1) In May 2018, SL Green 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, which 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 $11.1 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."

Properties Held for Sale and 35

Properties Held for Sale and Property Dispositions (Tables)	6 Months Ended
	Jun. 30, 2018
Discontinued Operations and Disposal Groups [Abstract]
Summary of properties sold	The following table summarizes the properties sold during the six months ended June 30, 2018 : Property Disposition Date Property Type Approximate Square Feet Sales Price (1) (in millions) Gain (loss) (2) (in millions) 600 Lexington Avenue January 2018 Fee Interest 303,515 $ 305.0 $ 23.8 115-117 Stevens Avenue May 2018 Fee Interest 178,000 12.0 (0.7 ) 635 Madison Avenue June 2018 Fee Interest 176,530 153.0 (14.1 ) (1) Sales price represents the gross sales price for a property or the gross asset valuation for interests in a property. (2) Gain (loss) on sale amounts do not include adjustments for expenses recorded in subsequent periods.

Debt and Preferred Equity Inv36

Debt and Preferred Equity Investments (Tables)	6 Months Ended
	Jun. 30, 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 for the six months ended June 30, 2018 and the twelve months ended December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Balance at beginning of period (1) $ 2,114,041 $ 1,640,412 Debt investment originations/accretion (2) 611,686 1,142,591 Preferred equity investment originations/accretion (2) 4,177 144,456 Redemptions/sales/syndications/amortization (3) (561,389 ) (813,418 ) Balance at end of period (1) $ 2,168,515 $ 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 are included in other assets and other liabilities on the consolidated balance sheets.
Summary of debt investments	As of June 30, 2018 and December 31, 2017 , we held the following debt investments with an aggregate weighted average current yield of 9.06% at June 30, 2018 (in thousands): Loan Type June 30, 2018 June 30, 2018 Senior June 30, 2018 (1) December 31, 2017 (1) Maturity (2) Fixed Rate Investments: Mortgage Loan (3)(4) $ — $ — $ 26,394 $ 26,366 February 2019 Mortgage Loan — — 164 239 August 2019 Mezzanine Loan (5a) — 1,160,000 208,506 204,005 March 2020 Mezzanine Loan — 15,000 3,500 3,500 September 2021 Mezzanine Loan — 147,000 24,922 24,913 April 2022 Mezzanine Loan — 280,000 35,564 34,600 August 2022 Mezzanine Loan (6) — 86,201 12,702 12,699 November 2023 Mezzanine Loan (5b) — 115,000 12,936 12,932 June 2024 Mezzanine Loan — 95,000 30,000 30,000 January 2025 Mezzanine Loan — 340,000 15,000 15,000 November 2026 Mezzanine Loan — 1,657,500 55,250 55,250 June 2027 Mortgage/Jr. Mortgage Loan (7) — — — 250,464 Total fixed rate $ — $ 3,895,701 $ 424,938 $ 669,968 Floating Rate Investments: Mezzanine Loan — 20,523 10,970 10,934 August 2018 Mortgage/Mezzanine Loan (8) — — 19,990 19,940 August 2018 Mezzanine Loan (9) — 65,000 14,992 14,955 August 2018 Mortgage/Mezzanine Loan — — 16,992 16,969 September 2018 Mezzanine Loan (10) — 37,500 14,961 14,855 September 2018 Mezzanine Loan 2,325 45,025 35,072 34,879 October 2018 Mezzanine Loan (5c) — 150,000 15,347 15,381 December 2018 Mezzanine Loan (5d) — — 14,836 14,869 December 2018 Mezzanine Loan — 33,000 26,967 26,927 December 2018 Mezzanine Loan — 175,000 59,873 59,723 December 2018 Mezzanine Loan (11) — 45,000 12,211 12,174 January 2019 Mezzanine Loan 4,000 29,291 9,980 8,550 January 2019 Mezzanine Loan (5e)(12) 795 — 15,150 15,148 March 2019 Mezzanine Loan — 38,000 21,964 21,939 March 2019 Mezzanine Loan (13) — 40,000 19,958 19,982 April 2019 Mezzanine Loan (13) — 61,130 21,718 34,947 April 2019 Mezzanine Loan — 175,000 37,355 37,250 April 2019 Mezzanine Loan — 265,000 24,895 24,830 April 2019 Mortgage/Jr. Mortgage Participation Loan 20,065 220,572 79,551 71,832 August 2019 Mezzanine Loan (10) 2,034 189,829 37,884 37,851 September 2019 Mortgage/Mezzanine Loan 20,560 — 168,369 143,919 September 2019 Mezzanine Loan — 350,000 34,810 34,737 October 2019 Mortgage/Mezzanine Loan 1,306 — 46,168 — December 2019 Mortgage/Mezzanine Loan 17,627 — 51,981 43,845 January 2020 Mezzanine Loan 1,123 571,863 78,462 75,834 January 2020 Mortgage Loan 14,786 — 84,783 — February 2020 Mezzanine Loan 3,878 306,711 50,669 — March 2020 Mortgage/Mezzanine Loan 45,019 — 333,290 — April 2020 Mezzanine Loan 6,386 35,912 11,829 11,259 July 2020 Loan Type June 30, 2018 June 30, 2018 Senior June 30, 2018 (1) December 31, 2017 (1) Maturity (2) Mezzanine Loan 44,088 340,558 83,065 75,428 November 2020 Mortgage and Mezzanine Loan 38,200 — 93,498 88,989 December 2020 Mortgage and Mezzanine Loan — — 35,207 35,152 December 2020 Jr. Mortgage Participation/Mezzanine Loan — 60,000 15,648 15,635 July 2021 Mortgage/Mezzanine Loan (14) — — — 162,553 Mortgage/Mezzanine Loan (14) — — — 74,755 Mortgage/Mezzanine Loan (15) — — — 23,609 Total floating rate $ 222,192 $ 3,254,914 $ 1,598,445 $ 1,299,650 Total $ 222,192 $ 7,150,615 $ 2,023,383 $ 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) In September 2014, we acquired a $26.4 million mortgage loan at a $0.2 million discount and a $5.7 million junior mortgage participation at a $5.7 million discount. The junior mortgage participation has been a nonperforming loan since acquisition, is currently on non-accrual status and has no carrying value. (4) This loan was repaid in August 2018. (5) Carrying value is net of the following amounts that were sold or syndicated, which are included in other assets and other liabilities on the consolidated balance sheets as a result of the transfers not meeting the conditions for sale accounting: (a) $1.3 million , (b) $12.0 million , (c) $14.6 million , (d) $14.1 million , and (e) $5.1 million . (6) The loan's June interest payment was outstanding at June 30, 2018 and was subsequently received in July 2018. 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. (7) 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. (8) This loan was extended in August 2018. (9) This loan was extended in July 2018. (10) This loan was repaid in July 2018. (11) In July 2018, the Company accepted an assignment of the property in-lieu of repayment of the loan, and marked the assets received and liabilities assumed to fair value, which exceeded the carrying value of the loan. (12) This loan was extended in March 2018. (13) This loan was extended in April 2018. (14) This loan was repaid in February 2018.
Summary of preferred equity investments	As of June 30, 2018 and December 31, 2017 , we held the following preferred equity investments with an aggregate weighted average current yield of 5.73% at June 30, 2018 (in thousands): Type June 30, 2018 June 30, 2018 Senior June 30, 2018 (1) December 31, 2017 (1) Maturity (2) Preferred Equity $ — $ 272,000 $ 145,132 $ 144,423 April 2021 Total $ — $ 272,000 $ 145,132 $ 144,423 (1) Carrying value is net of deferred origination fees. (2) Represents contractual maturity, excluding any unexercised extension options.

Investments in Unconsolidated37

Investments in Unconsolidated Joint Ventures (Tables)	6 Months Ended
	Jun. 30, 2018
Schedule of Equity Method Investments [Line Items]
Schedule of general information on joint ventures	As of June 30, 2018 and December 31, 2017, the carrying value for acquisition, development and construction arrangements were as follows (in thousands): Loan Type June 30, 2018 December 31, 2017 Maturity Date Preferred Equity $ 141,000 $ — September 2018 Mezzanine Loan (1) 44,483 44,823 February 2022 Mezzanine Loan (2) 28,105 26,716 July 2036 Mezzanine Loan and Preferred Equity (3) — 100,000 $ 213,588 $ 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 Company was redeemed on this investment in July 2018. (3) The mezzanine loan was repaid and the preferred equity interest was redeemed in March 2018. The table below provides general information on each of our joint ventures as of June 30, 2018 : Property Partner Ownership (1) Economic (1) Unaudited Approximate Square Feet Acquisition Date (2) Acquisition (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/ 30.00% 30.00% 17,150 December 2010 10,800 3 Columbus Circle (4) The Moinian Group 48.90% 48.90% 741,500 January 2011 500,000 280 Park Avenue Vornado Realty Trust 50.00% 50.00% 1,219,158 March 2011 400,000 1552-1560 Broadway (5) Jeff Sutton 50.00% 50.00% 57,718 August 2011 136,550 724 Fifth Avenue (6) Jeff Sutton 50.00% 50.00% 65,010 January 2012 223,000 10 East 53rd Street Canadian Pension Plan Investment Board 55.00% 55.00% 354,300 February 2012 252,500 521 Fifth Avenue Plaza Global 50.50% 50.50% 460,000 November 2012 315,000 21 East 66th Street (7) Private Investors 32.28% 32.28% 13,069 December 2012 75,000 650 Fifth Avenue (8) 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 (9) Various Various Various 1,439,016 February 2015 36,668 131-137 Spring Street Invesco Real Estate 20.00% 20.00% 68,342 August 2015 277,750 605 West 42nd Street The Moinian Group 20.00% 20.00% 927,358 April 2016 759,000 11 Madison Avenue PGIM Real Estate 60.00% 60.00% 2,314,000 August 2016 2,605,000 333 East 22nd Street Private Investors 33.33% 33.33% 26,926 August 2016 — 400 East 57th Street (10) BlackRock, Inc and Stonehenge Partners 51.00% 41.00% 290,482 October 2016 170,000 One Vanderbilt (11) National Pension Service of Korea/Hines Interest LP 71.01% 71.01% — January 2017 3,310,000 Mezzanine Loan (12) Private Investors 33.33% 33.33% — May 2017 15,000 Worldwide Plaza RXR Realty / New York REIT / Private Investor 24.35% 24.35% 2,048,725 October 2017 1,725,000 1515 Broadway (13) Allianz Real Estate of America 56.87% 56.87% 1,750,000 November 2017 1,950,000 (1) Ownership interest and economic interest represent the Company's interests in the joint venture as of June 30, 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) As a result of the sale of a condominium interest in September 2012, Young & Rubicam, Inc., or Y&R, owns floors three through eight at the property. Because the joint venture has an option to repurchase these floors, the gain associated with this sale was deferred. (5) The purchase price represents only the purchase of the 1552 Broadway interest which comprised approximately 13,045 square feet. The joint venture also owns a long-term leasehold interest in the retail space and certain other spaces at 1560 Broadway, which is adjacent to 1552 Broadway. (6) In July 2018, the Company closed on the sale of substantially all of its interest in 724 Fifth Avenue to its joint venture partner. (7) 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. (8) 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. (9) 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. (10) 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. (11) The partners have committed aggregate equity 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 June 30, 2018 the total of the two partners' ownership interests based on equity contributed was 13.39% . (12) In May 2017, the Company contributed a mezzanine loan secured by a commercial property in midtown Manhattan to a joint venture and retained a 33.33% interest in the venture. The carrying value is net of $10.0 million that was sold, which is included in other assets and other liabilities on the consolidated balance sheets as a result of the transfers not meeting the conditions for sale accounting. The loan was repaid in August 2018. (13) 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.
Schedule of first mortgage notes payable collateralized by the respective joint venture properties and assignment of leases	The first mortgage notes and other loans payable collateralized by the respective joint venture properties and assignment of leases at June 30, 2018 and December 31, 2017 , respectively, are as follows (amounts in thousands): Property Economic (1) Maturity Date Interest Rate (2) June 30, 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 — 3 Columbus Circle 48.90 % March 2025 3.61 % 350,000 350,000 1515 Broadway 56.87 % March 2025 3.93 % 864,238 872,528 11 Madison Avenue 60.00 % September 2025 3.84 % 1,400,000 1,400,000 800 Third Avenue 60.52 % February 2026 3.37 % 177,000 177,000 400 East 57th Street 41.00 % November 2026 3.00 % 100,000 100,000 Worldwide Plaza 24.35 % November 2027 3.98 % 1,200,000 1,200,000 Stonehenge Portfolio (5) Various Various 4.20 % 323,058 357,282 Total fixed rate debt $ 6,026,624 $ 5,569,138 Floating Rate Debt: 724 Fifth Avenue (6) 50.00 % April 2019 L+ 2.42 % $ 275,000 $ 275,000 280 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 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 (7) 25.00 % November 2020 L+ 2.13 % 174,430 171,444 11 West 34th Street 30.00 % January 2021 L+ 1.45 % 23,000 23,000 100 Park Avenue 49.90 % February 2021 L+ 1.75 % 360,000 360,000 One Vanderbilt (8) 71.01 % September 2021 L+ 3.50 % 375,000 355,535 605 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 % 1,608 1,648 Stonehenge Portfolio Various January 2021 L+ 1.40 % 38,000 55,340 175-225 Third Street (9) — 40,000 1745 Broadway (10) — 345,000 Jericho Plaza (11) — 81,099 Total floating rate debt $ 3,518,038 $ 3,979,066 Total joint venture mortgages and other loans payable $ 9,544,662 $ 9,548,204 Deferred financing costs, net (110,924 ) (136,103 ) Total joint venture mortgages and other loans payable, net $ 9,433,738 $ 9,412,101 (1) Economic interest represents the Company's interests in the joint venture as of June 30, 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 rates as of June 30, 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 $135.7 million , $54.8 million , and $132.6 million in fixed-rate mortgages that mature in August 2019, June 2024, and April 2028, respectively. (6) In July 2018, the Company closed on the sale of substantially all of its interest in 724 Fifth Avenue to its joint venture partner. (7) This loan has a committed amount of $195.0 million , of which $20.6 million was unfunded as of June 30, 2018 . (8) This loan is a $1.5 billion construction facility, which bears interest at 350 basis points over 30-day LIBOR, 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. (9) In April 2018, along with our joint venture partner, we closed on the sale of the property. (10) In May 2018, along with our joint venture partner, we closed on the sale of the property. (11) In June 2018, we closed on the sale of our interest in the property.
Schedule of combined balance sheets for the unconsolidated joint ventures	The combined balance sheets for the unconsolidated joint ventures, at June 30, 2018 and December 31, 2017 are as follows (in thousands): June 30, 2018 December 31, 2017 Assets (1) Commercial real estate property, net $ 14,193,325 $ 12,822,133 Cash and restricted cash 434,307 494,909 Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance 308,653 349,944 Debt and preferred equity investments, net 228,588 202,539 Other assets 2,254,990 1,407,806 Total assets $ 17,419,863 $ 15,277,331 Liabilities and equity (1) Mortgages and other loans payable, net $ 9,433,738 $ 9,412,101 Deferred revenue/gain 1,863,384 985,648 Other liabilities 478,916 411,053 Equity 5,643,825 4,468,529 Total liabilities and equity $ 17,419,863 $ 15,277,331 Company's investments in unconsolidated joint ventures $ 3,059,985 $ 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.
Schedule of combined statements of income for the unconsolidated joint ventures	The combined statements of operations for the unconsolidated joint ventures, for the three and six months ended June 30, 2018 and 2017 , are as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Total revenues $ 314,195 $ 210,590 $ 635,136 $ 427,109 Operating expenses 50,356 39,147 110,129 77,941 Ground rent 4,457 4,179 8,850 8,430 Real estate taxes 55,838 35,170 112,865 70,109 Interest expense, net of interest income 91,648 59,702 181,389 115,030 Amortization of deferred financing costs 7,350 7,458 12,466 13,963 Transaction related costs — 56 — 146 Depreciation and amortization 111,495 65,944 216,575 137,109 Total expenses 321,144 211,656 642,274 422,728 Net (loss) income before gain on sale (1) $ (6,949 ) $ (1,066 ) $ (7,138 ) $ 4,381 Company's equity in net income from unconsolidated joint ventures (1) $ 4,702 $ 3,412 $ 8,738 $ 10,026 (1) The combined statements of operation 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 [Member]
Schedule of Equity Method Investments [Line Items]
Schedule of general information on joint ventures	The following table summarizes the investments in unconsolidated joint ventures sold during the six months ended June 30, 2018 : Property Ownership Interest Disposition Date Type of Sale Gross Asset Valuation (in thousands) (1) Gain (Loss) on Sale (in thousands) (2) 1274 Fifth Avenue (3) 9.83% February 2018 Property $ 44,100 $ (362 ) 1515 Broadway (4) 13.00% February 2018 Ownership Interest 1,950,000 — Stonehenge Village (3) 5.00% March 2018 Property 287,000 (5,701 ) 175-225 Third Street Brooklyn, New York 95.00% April 2018 Property 115,000 19,483 1745 Broadway 56.87% May 2018 Property 633,000 52,038 Jericho Plaza 11.67% June 2018 Ownership Interest 117,400 147 (1) Represents implied gross valuation for the joint venture or sales price of the property. (2) Represents the Company's share of the gain (loss). (3) Property was part of the Stonehenge Portfolio. (4) Our investment in 1515 Broadway was marked to fair value on January 1, 2018 upon adoption of ASC 610-20.

Deferred Costs (Tables)

Deferred Costs (Tables)	6 Months Ended
	Jun. 30, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of components of deferred costs	Deferred costs at June 30, 2018 and December 31, 2017 consisted of the following (in thousands): June 30, 2018 December 31, 2017 Deferred leasing costs $ 426,875 $ 443,341 Less: accumulated amortization (227,934 ) (217,140 ) Deferred costs, net $ 198,941 $ 226,201

Mortgages and Other Loans Pay39

Mortgages and Other Loans Payable (Tables)	6 Months Ended
	Jun. 30, 2018
Mortgages and Other Loans Payable
Schedule of first mortgages and other loans payable collateralized by the respective properties and assignment of leases	The first mortgages and other loans payable collateralized by the respective properties and assignment of leases or debt investments at June 30, 2018 and December 31, 2017 , respectively, were as follows (amounts in thousands): Property Maturity Date Interest Rate (1) June 30, 2018 December 31, 2017 Fixed Rate Debt: One Madison Avenue May 2020 5.91 % $ 469,564 $ 486,153 762 Madison Avenue February 2022 5.00 % 771 771 100 Church Street July 2022 4.68 % 215,223 217,273 420 Lexington Avenue October 2024 3.99 % 300,000 300,000 400 East 58th Street (2) November 2026 3.00 % 40,000 40,000 Landmark Square January 2027 4.90 % 100,000 100,000 485 Lexington Avenue February 2027 4.25 % 450,000 450,000 1080 Amsterdam (3) February 2027 3.58 % 36,138 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 Total fixed rate debt $ 1,861,696 $ 2,400,560 Floating Rate Debt: 719 Seventh Avenue February 2019 L+ 3.05 % $ 44,000 $ 41,622 183, 187 Broadway & 5-7 Dey Street (7) May 2019 L+ 2.70 % 58,000 58,000 2017 Master Repurchase Agreement (8) June 2019 L+ 2.34 % 300,000 90,809 220 East 42nd Street October 2020 L+ 1.60 % 275,000 275,000 Total floating rate debt $ 677,000 $ 465,431 Total fixed rate and floating rate debt $ 2,538,696 $ 2,865,991 Mortgages reclassed to liabilities related to assets held for sale — — Total mortgages and other loans payable $ 2,538,696 $ 2,865,991 Deferred financing costs, net of amortization (21,599 ) (28,709 ) Total mortgages and other loans payable, net $ 2,517,097 $ 2,837,282 (1) Interest rate as of June 30, 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 property. (6) In June 2018, the Series J Preferred Units were redeemed in connection with the sale of the property. (7) In May 2018, we exercised a 12 -month extension option. (8) In June 2018, we exercised a 12 -month extension option.

Corporate Indebtedness (Tables)

Corporate Indebtedness (Tables)	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Schedule of senior unsecured notes and other related disclosures by scheduled maturity date	The following table sets forth our senior unsecured notes and other related disclosures as of June 30, 2018 and December 31, 2017 , respectively, by scheduled maturity date (amounts in thousands): Issuance June 30, June 30, December 31, Coupon Rate (1) Initial Term (in Years) Maturity Date August 5, 2011 (2) $ 250,000 $ 249,991 $ 249,953 5.00 % 7 August 2018 March 16, 2010 (2) 250,000 250,000 250,000 7.75 % 10 March 2020 October 5, 2017 (3) 500,000 499,539 499,489 3.25 % 5 October 2022 November 15, 2012 (4) 300,000 304,673 305,163 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 $ 1,400,000 $ 1,404,203 $ 1,404,605 Deferred financing costs, net (7,481 ) (8,666 ) $ 1,400,000 $ 1,396,722 $ 1,395,939 (1) Interest on the senior unsecured notes is payable semi-annually with principal and unpaid interest due on the scheduled maturity dates. (2) Issued by the Company, the Operating Partnership and ROP, as co-obligors. (3) Issued by the Operating Partnership with the Company and ROP as guarantors. (4) In October 2017, the Company, the Operating Partnership and ROP, as co-obligors, issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022. The notes were priced at 105.334% .
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 June 30, 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 Remaining 2018 $ 19,097 $ — $ — $ — $ — $ 250,000 $ 269,097 $ 4,986 2019 42,271 102,000 — — — — 144,271 252,795 2020 23,466 979,531 — — — 250,000 1,252,997 276,006 2021 11,638 — — — — — 11,638 454,621 2022 9,430 198,555 — — — 800,000 1,007,985 220,810 Thereafter 16,591 1,136,117 360,000 1,500,000 100,000 100,000 3,212,708 2,879,344 $ 122,493 $ 2,416,203 $ 360,000 $ 1,500,000 $ 100,000 $ 1,400,000 $ 5,898,696 $ 4,088,562
Schedule of consolidated interest expense, excluding capitalized interest	Consolidated interest expense, excluding capitalized interest, was comprised of the following (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Interest expense before capitalized interest $ 61,553 $ 71,992 $ 116,471 $ 144,414 Interest capitalized (7,594 ) (6,743 ) (14,280 ) (13,022 ) Interest income (348 ) (393 ) (664 ) (914 ) Interest expense, net $ 53,611 $ 64,856 $ 101,527 $ 130,478

Related Party Transactions (Tab

Related Party Transactions (Tables)	6 Months Ended
	Jun. 30, 2018
Related Party Transactions [Abstract]
Schedule of amounts due from/to related parties	Amounts due from joint ventures and related parties at June 30, 2018 and December 31, 2017 consisted of the following (in thousands): June 30, 2018 December 31, 2017 Due from joint ventures $ 17,446 $ 15,025 Other 10,408 8,014 Related party receivables $ 27,854 $ 23,039

Noncontrolling Interests on t42

Noncontrolling Interests on the Company's Consolidated Financial Statements (Tables)	6 Months Ended
	Jun. 30, 2018
Noncontrolling Interest [Abstract]
Schedule of Noncontrolling Interest	Below is a summary of the activity relating to the noncontrolling interests in the Operating Partnership for the six months ended June 30, 2018 and the twelve months ended December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Balance at beginning of period $ 461,954 $ 473,882 Distributions (7,712 ) (14,266 ) Issuance of common units 17,714 25,723 Redemption of common units (1,561 ) (21,574 ) Net income 10,858 3,995 Accumulated other comprehensive income allocation 864 (94 ) Fair value adjustment 4,493 (5,712 ) Balance at end of period $ 486,610 $ 461,954
Schedule of Preferred Unit Activity	Below is a summary of the activity relating to the preferred units in the Operating Partnership for the three months ended June 30, 2018 and the twelve months ended December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Balance at beginning of period $ 301,735 $ 302,010 Issuance of preferred units — — Redemption of preferred units (350 ) (275 ) Balance at end of period $ 301,385 $ 301,735

Stockholders' Equity of the C43

Stockholders' Equity of the Company (Tables)	6 Months Ended
	Jun. 30, 2018
Stockholders' Equity Note [Abstract]
Class of Treasury Stock	At June 30, 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 Maximum approximate dollar value of shares that may yet be repurchased under the plan (in millions) (1) 2017 8,342,411 $101.64 8,342,411 $1,152.0 First quarter 2018 3,653,928 $97.07 11,996,339 $797.2 Second quarter 2018 (2) 3,479,552 $97.22 15,475,891 $458.9 (1) Reflective of $2.0 billion plan maximum as of June 30, 2018 . (2) Includes 101,421 shares of common stock repurchased by the Company in June 2018 that were settled in July 2018.
Schedule of Common Stock Issued and Proceeds Received Dividend Reinvestments	The following table summarizes SL Green common stock issued, and proceeds received from dividend reinvestments and/or stock purchases under the DRSPP for the six months ended June 30, 2018 and 2017 , respectively (dollars in thousands): Six Months Ended June 30, 2018 2017 Shares of common stock issued 674 1,036 Dividend reinvestments/stock purchases under the DRSPP $ 64 $ 111
Schedule of Earnings Per Share	SL Green's earnings per share for the three and six months ended June 30, 2018 and 2017 are computed as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, Numerator 2018 2017 2018 2017 Basic Earnings: Income attributable to SL Green common stockholders $ 103,556 $ 8,222 $ 205,322 $ 19,573 Effect of Dilutive Securities: Redemption of units to common shares 5,586 419 10,858 895 Diluted Earnings: Income attributable to SL Green common stockholders $ 109,142 $ 8,641 $ 216,180 $ 20,468 Three Months Ended June 30, Six Months Ended June 30, Denominator 2018 2017 2018 2017 Basic Shares: Weighted average common stock outstanding 87,176 99,900 88,772 100,268 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,706 4,562 4,695 4,584 Stock-based compensation plans 201 270 200 288 Diluted weighted average common stock outstanding 92,083 104,732 93,667 105,140

Partners' Capital of the Oper44

Partners' Capital of the Operating Partnership (Tables)	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Schedule of calculation of numerator and denominator in earnings per unit	The Operating Partnership's earnings per unit for the three and six months ended June 30, 2018 and 2017 , respectively, are computed as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, Numerator 2018 2017 2018 2017 Basic and Diluted Earnings: Income attributable to SLGOP common unitholders $ 109,142 $ 8,641 $ 216,180 $ 20,468 Three Months Ended June 30, Six Months Ended June 30, Denominator 2018 2017 2018 2017 Basic units: Weighted average common units outstanding 91,882 104,462 93,467 104,852 Effect of Dilutive Securities: Stock-based compensation plans 201 270 200 288 Diluted weighted average common units outstanding 92,083 104,732 93,667 105,140

Share-based Compensation (Table

Share-based Compensation (Tables)	6 Months Ended
	Jun. 30, 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 six months ended June 30, 2018 and the year ended December 31, 2017 . June 30, 2018 December 31, 2017 Dividend yield 2.85 % 2.51 % Expected life 3.5 years 4.4 years Risk-free interest rate 2.48 % 1.73 % Expected stock price volatility 22.00 % 28.10 %
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 June 30, 2018 and December 31, 2017 , and changes during the six months ended June 30, 2018 and year ended December 31, 2017 are as follows: June 30, 2018 December 31, 2017 Options Outstanding Weighted Average Exercise Price Options Outstanding Weighted Average Exercise Price Balance at beginning of period 1,548,719 $ 101.48 1,737,213 $ 98.44 Granted 6,000 97.91 174,000 105.66 Exercised (58,734 ) 89.62 (292,193 ) 81.07 Lapsed or canceled (56,033 ) 114.70 (70,301 ) 121.68 Balance at end of period 1,439,952 $ 101.43 1,548,719 $ 101.48 Options exercisable at end of period 1,067,969 $ 98.93 800,902 $ 94.33 Total fair value of options granted during the period $ 84,068 $ 3,816,652
Summary of restricted stock and charges during the period	A summary of the Company's restricted stock as of June 30, 2018 and December 31, 2017 and charges during the six months ended June 30, 2018 and the year ended December 31, 2017 , are as follows: June 30, 2018 December 31, 2017 Balance at beginning of period 3,298,216 3,202,031 Granted 1,700 96,185 Canceled (8,300 ) — Balance at end of period 3,291,616 3,298,216 Vested during the period 92,114 95,736 Compensation expense recorded $ 6,251,350 $ 9,809,749 Total fair value of restricted stock granted during the period $ 163,831 $ 9,905,986

Accumulated Other Comprehensi46

Accumulated Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Schedule of accumulated other comprehensive income (loss)	The following tables set forth the changes in accumulated other comprehensive income (loss) by component as of June 30, 2018 (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, 2017 $ 12,542 $ 5,020 $ 1,042 $ 18,604 Other comprehensive (loss) income before reclassifications 9,837 4,097 (14 ) 13,920 Amounts reclassified from accumulated other comprehensive income 237 (139 ) — 98 Balance at June 30, 2018 $ 22,616 $ 8,978 $ 1,028 $ 32,622 (1) Amount reclassified from accumulated other comprehensive income (loss) is included in interest expense in the respective consolidated statements of operations. As of June 30, 2018 and December 31, 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 $2.2 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)	6 Months Ended
	Jun. 30, 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 June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 28,570 $ — $ 28,570 $ — Interest rate cap and swap agreements (included in other assets) $ 26,132 $ — $ 26,132 $ — 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 June 30, 2018 and December 31, 2017 (in thousands): June 30, 2018 December 31, 2017 Carrying Value (1) Fair Value Carrying Value (1) Fair Value Debt and preferred equity investments $ 2,168,515 (2) $ 2,114,041 (2) Fixed rate debt $ 3,765,899 $ 3,796,225 $ 4,305,165 $ 4,421,866 Variable rate debt 2,137,000 2,151,998 1,605,431 1,612,224 $ 5,902,899 $ 5,948,223 $ 5,910,596 $ 6,034,090 (1) Amounts exclude net deferred financing costs. (2) At June 30, 2018 , debt and preferred equity investments had an estimated fair value ranging between $2.2 billion and $2.4 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_ Deriva48

Financial Instruments: Derivatives and Hedging (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 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 $ 15,272 Interest Rate Swap 100,000 1.161 % July 2016 July 2023 Other Assets 7,496 Interest Rate Cap 137,500 4.000 % September 2017 September 2019 Other Assets 1 Interest Rate Swap 100,000 1.928 % December 2017 November 2020 Other Assets 1,688 Interest Rate Swap 100,000 1.934 % December 2017 November 2020 Other Assets 1,675 $ 26,132
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 three months ended June 30, 2018 and 2017 , respectively (in thousands): Amount of Gain (Loss) Location of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income Amount of Gain (Loss) Location of Gain (Loss) Recognized in Income on Derivative Amount of Gain (Loss) Three Months Ended June 30, Three Months Ended June 30, Three Months Ended June 30, Derivative 2018 2017 2018 2017 2018 2017 Interest Rate Swaps/Caps $ 3,116 $ (2,036 ) Interest expense $ 76 $ (519 ) Interest expense $ (3 ) $ — Share of unconsolidated joint ventures' derivative instruments 1,092 (1,328 ) Equity in net income from unconsolidated joint ventures 155 (292 ) Equity in net income from unconsolidated joint ventures (30 ) 34 $ 4,208 $ (3,364 ) $ 231 $ (811 ) $ (33 ) $ 34 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 six months ended June 30, 2018 and 2017 , respectively (in thousands): Amount of Gain (Loss) Recognized in Other Comprehensive Loss (Effective Portion) Location of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion) Location of Gain (Loss) Recognized in Income on Derivative Amount of Gain (Loss) Recognized into Income (Ineffective Portion) Six Months Ended June 30, Six Months Ended June 30, Six Months Ended June 30, Derivative 2018 2017 2018 2017 2018 2017 Interest Rate Swaps/Caps $ 10,398 $ (5,173 ) Interest expense $ (253 ) $ (1,498 ) Interest expense $ (12 ) $ (8 ) Share of unconsolidated joint ventures' derivative instruments 4,405 (987 ) Equity in net income from unconsolidated joint ventures 154 (691 ) Equity in net income from unconsolidated joint ventures (119 ) (61 ) $ 14,803 $ (6,160 ) $ (99 ) $ (2,189 ) $ (131 ) $ (69 )

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2018 (in thousands): Capital lease Non-cancellable operating leases Remaining 2018 $ 5,324 $ 17,917 2019 10,826 35,943 2020 11,245 36,435 2021 11,635 36,751 2022 11,856 34,723 2023 12,083 32,548 Thereafter 1,391,127 1,008,718 Total minimum lease payments $ 1,454,096 $ 1,203,035 Amount representing interest (1,145,484 ) Amount classified within liabilities held for sale (1) (265,391 ) Capital lease obligations $ 43,221
Schedule of future minimum rental 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 June 30, 2018 (in thousands): Capital lease Non-cancellable operating leases Remaining 2018 $ 5,324 $ 17,917 2019 10,826 35,943 2020 11,245 36,435 2021 11,635 36,751 2022 11,856 34,723 2023 12,083 32,548 Thereafter 1,391,127 1,008,718 Total minimum lease payments $ 1,454,096 $ 1,203,035 Amount representing interest (1,145,484 ) Amount classified within liabilities held for sale (1) (265,391 ) Capital lease obligations $ 43,221 (1) Related to the ground lease at 2 Herald Square, which is under contract for sale of a joint venture interest and has been classified as held for sale as of June 30, 2018.

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Schedule of selected results of operations and selected asset information	Selected consolidated results of operations for the three and six months ended June 30, 2018 and 2017 , and selected asset information as of June 30, 2018 and December 31, 2017 , regarding our operating segments are as follows (in thousands): Real Estate Segment Debt and Preferred Equity Segment Total Company Total revenues Three months ended: June 30, 2018 $ 251,843 $ 49,273 $ 301,116 June 30, 2017 337,528 60,622 398,150 Six months ended: June 30, 2018 508,248 94,563 602,811 June 30, 2017 674,610 100,921 775,531 Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities Three months ended: June 30, 2018 $ 13,239 $ 34,276 $ 47,515 June 30, 2017 (16,232 ) 52,045 35,813 Six months ended: June 30, 2018 27,263 67,701 94,964 June 30, 2017 (2,425 ) 89,558 87,133 Total assets As of: June 30, 2018 $ 11,249,972 $ 2,463,956 $ 13,713,928 December 31, 2017 11,631,700 2,351,204 13,982,904
Schedule of reconciliation of income from continuing operations to net income attributable to SL Green common stockholders	The table below reconciles net income before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities to net income for the three and six months ended June 30, 2018 and 2017 (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2018 2017 2018 2017 Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities $ 47,515 $ 35,813 $ 94,964 $ 87,133 Equity in net gain on sale of interest in unconsolidated joint venture/real estate 72,025 13,089 65,585 15,136 Purchase price and other fair value adjustments 11,149 — 60,442 — (Loss) gain on sale of real estate, net (14,790 ) (3,823 ) 8,731 (3,256 ) Depreciable real estate reserves — (29,064 ) — (85,336 ) Gain on sale of investment in marketable securities — — — 3,262 Net income $ 115,899 $ 16,015 $ 229,722 $ 16,939

Organization and Basis of Pre51

Organization and Basis of Presentation - Additional Information (Details) - USD ($)	Aug. 07, 2018	Jun. 30, 2018	Dec. 31, 2017
SL Green Operating Partnership
Organization
Percentage of ownership in SL Green Management LLC owned by operating partnership (percent)		100.00%
Noncontrolling interest in the operating partnership (as a percent)		5.20%	4.58%
Subsequent Event | Senior Unsecured Notes Due August 2021 | Senior Unsecured Notes
Organization
Face amount of loan	$ 350,000,000
Interest rate added to base rate (as a percent)	0.98%

Organization and Basis of Pre52

Organization and Basis of Presentation - Schedule of Commercial Office Properties (Details) $ in Billions	6 Months Ended
	Jun. 30, 2018USD ($)ft²buildingshares
Real estate properties
Number of Properties | building	90
Approximate Square Feet unaudited (sqft)	31,150,063
Weighted Average Occupancy unaudited (as a percent)	91.90%
Debt and preferred equity investments including investments held by unconsolidated joint ventures | $	$ 2.4
Debt and preferred equity investments and other financing receivables included in other balance sheet items | $	$ 0.2
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	77
Approximate Square Feet unaudited (sqft)	28,521,207
Weighted Average Occupancy unaudited (as a percent)	92.10%
Residential
Real estate properties
Number of Properties | building	13
Approximate Square Feet unaudited (sqft)	2,628,856
Weighted Average Occupancy unaudited (as a percent)	90.00%
Managed office properties
Real estate properties
Approximate Square Feet unaudited (sqft)	336,000
Consolidated properties
Real estate properties
Number of Properties | building	57
Approximate Square Feet unaudited (sqft)	16,737,964
Consolidated properties | Commercial properties
Real estate properties
Number of Properties | building	54
Approximate Square Feet unaudited (sqft)	16,265,859
Consolidated properties | Residential
Real estate properties
Number of Properties | building	3
Approximate Square Feet unaudited (sqft)	472,105
Unconsolidated properties
Real estate properties
Number of Properties | building	33
Approximate Square Feet unaudited (sqft)	14,412,099
Unconsolidated properties | Commercial properties
Real estate properties
Number of Properties | building	23
Approximate Square Feet unaudited (sqft)	12,255,348
Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	10
Approximate Square Feet unaudited (sqft)	2,156,751
Manhattan
Real estate properties
Number of Properties | building	56
Approximate Square Feet unaudited (sqft)	25,633,007
Weighted Average Occupancy unaudited (as a percent)	92.60%
Manhattan | Office
Real estate properties
Number of Properties | building	31
Approximate Square Feet unaudited (sqft)	24,247,255
Weighted Average Occupancy unaudited (as a percent)	94.10%
Manhattan | Retail
Real estate properties
Number of Properties | building	13
Approximate Square Feet unaudited (sqft)	650,553
Weighted Average Occupancy unaudited (as a percent)	94.20%
Manhattan | Development/Redevelopment
Real estate properties
Number of Properties | building	11
Approximate Square Feet unaudited (sqft)	735,199
Weighted Average Occupancy unaudited (as a percent)	43.90%
Manhattan | Fee Interest
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	0
Weighted Average Occupancy unaudited (as a percent)	0.00%
Manhattan | Residential
Real estate properties
Number of Properties | building	13
Approximate Square Feet unaudited (sqft)	2,628,856
Weighted Average Occupancy unaudited (as a percent)	90.00%
Manhattan | Consolidated properties
Real estate properties
Number of Properties | building	33
Approximate Square Feet unaudited (sqft)	13,377,659
Manhattan | Consolidated properties | Office
Real estate properties
Number of Properties | building	21
Approximate Square Feet unaudited (sqft)	12,756,091
Manhattan | Consolidated properties | Retail
Real estate properties
Number of Properties | building	4
Approximate Square Feet unaudited (sqft)	302,583
Manhattan | Consolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	8
Approximate Square Feet unaudited (sqft)	318,985
Manhattan | Consolidated properties | Fee Interest
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0
Manhattan | Consolidated properties | Residential
Real estate properties
Number of Properties | building	3
Approximate Square Feet unaudited (sqft)	472,105
Manhattan | Consolidated properties | Dual property type, retail portion
Real estate properties
Approximate Square Feet unaudited (sqft)	270,132
Manhattan | Consolidated properties | Dual property type, residential portion
Real estate properties
Approximate Square Feet unaudited (sqft)	222,855
Manhattan | Unconsolidated properties
Real estate properties
Number of Properties | building	23
Approximate Square Feet unaudited (sqft)	12,255,348
Manhattan | Unconsolidated properties | Office
Real estate properties
Number of Properties | building	10
Approximate Square Feet unaudited (sqft)	11,491,164
Manhattan | Unconsolidated properties | Retail
Real estate properties
Number of Properties | building	9
Approximate Square Feet unaudited (sqft)	347,970
Manhattan | Unconsolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	3
Approximate Square Feet unaudited (sqft)	416,214
Manhattan | Unconsolidated properties | Fee Interest
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	0
Manhattan | Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	10
Approximate Square Feet unaudited (sqft)	2,156,751
Suburban
Real estate properties
Number of Properties | building	21
Approximate Square Feet unaudited (sqft)	2,888,200
Weighted Average Occupancy unaudited (as a percent)	87.20%
Suburban | Office
Real estate properties
Number of Properties | building	19
Approximate Square Feet unaudited (sqft)	2,835,200
Weighted Average Occupancy unaudited (as a percent)	87.00%
Suburban | Retail
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	52,000
Weighted Average Occupancy unaudited (as a percent)	100.00%
Suburban | Development/Redevelopment
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	1,000
Weighted Average Occupancy unaudited (as a percent)	0.00%
Suburban | Residential
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0
Weighted Average Occupancy unaudited (as a percent)	0.00%
Suburban | Consolidated properties
Real estate properties
Number of Properties | building	21
Approximate Square Feet unaudited (sqft)	2,888,200
Suburban | Consolidated properties | Office
Real estate properties
Number of Properties | building	19
Approximate Square Feet unaudited (sqft)	2,835,200
Suburban | Consolidated properties | Retail
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	52,000
Suburban | Consolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	1
Approximate Square Feet unaudited (sqft)	1,000
Suburban | Consolidated properties | Residential
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0
Suburban | Unconsolidated properties
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0
Suburban | Unconsolidated properties | Office
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0
Suburban | Unconsolidated properties | Retail
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0
Suburban | Unconsolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0
Suburban | Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	0
Approximate Square Feet unaudited (sqft)	0

Significant Accounting Polici53

Significant Accounting Policies - Investments in Commercial Real Estate Properties (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Investment in Commercial Real Estate Properties
Depreciable real estate reserves	$ 0	$ (29,064)	$ 0	$ (85,336)
Rental revenue from amortization of acquired leases	1,800	6,400	4,200	11,200
Reduction in interest expense from amortization of above-market rate mortgages	0	$ 700	0	$ 1,300
Identified intangible assets (included in other assets):
Gross amount	263,138		263,138		$ 325,880
Accumulated amortization	(239,344)		(239,344)		(277,038)
Net	23,794		23,794		48,842
Identified intangible liabilities (included in deferred revenue):
Gross amount	274,120		274,120		540,283
Accumulated amortization	(249,905)		(249,905)		(402,583)
Net	24,215		24,215		137,700
Net intangible assets reclassed to assets held for sale	100		100		13,900
Net intangible liabilities reclassed to liabilities relates to assets held for sale	$ 100		$ 100		$ 4,100
Minimum | Above-market leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)			1 year
Minimum | Below-market leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)			1 year
Minimum | In-place leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)			1 year
Maximum | Above-market leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)			14 years
Maximum | Below-market leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)			14 years
Maximum | In-place leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)			14 years
Building | Minimum
Investment in Commercial Real Estate Properties
Estimated useful life (in years)			3 years
Building | Maximum
Investment in Commercial Real Estate Properties
Estimated useful life (in years)			40 years

Significant Accounting Polici54

Significant Accounting Policies - Investment in Marketable Securities (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2018	Dec. 31, 2017
Investment in Marketable Securities
Marketable securities			$ 28,570,000	$ 28,579,000
Proceeds from sale of marketable securities	$ 54,400,000
Marketable Securities, Realized Gain (Loss)		$ 3,300,000
Fair Value
Investment in Marketable Securities
Marketable securities			28,570,000	28,579,000
Equity marketable securities
Investment in Marketable Securities
Cost basis			0	0
Commercial mortgage-backed securities
Investment in Marketable Securities
Marketable securities			28,570,000	28,579,000
Cost basis			$ 27,500,000	$ 27,500,000

Significant Accounting Polici55

Significant Accounting Policies - Reserve for Credit Losses (Details) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Accounting Policies [Abstract]
Loan reserves	$ 0	$ 0

Significant Accounting Polici56

Significant Accounting Policies - Revenue Recognition/Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Income taxes
Federal, state and local tax provision	$ 1.1	$ 1.6

Significant Accounting Polici57

Significant Accounting Policies - Concentrations of Credit Risk/Accounting Standards Updates (Details) $ in Billions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018USD ($)Tenant
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%	5.00%
Annualized rent | 1515 Broadway | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	5.80%
Annualized rent | 11 Madison Avenue | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	7.30%
Annualized rent | 1185 Avenue of the Americas | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	7.20%
Annualized rent | 420 Lexington Avenue | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	6.40%
Annualized rent | 1 Madison Ave | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	5.70%
Tenant 1 | Annualized rent | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)		8.20%
1515 Broadway | Accounting Standards Update 2017-05
Concentration of Credit Risk
Gain on disposal | $		$ 0.6

Property Acquisitions - Propert

Property Acquisitions - Properties Acquired (Details) $ in Millions	1 Months Ended
	May 31, 2018USD ($)ft²	Jun. 30, 2018ft²
Property Acquisitions
Approximate Square Feet | ft²		31,150,063
2 Herald Square
Property Acquisitions
Approximate Square Feet | ft²	369,000
Acquisition price | $	$ 266
Business combination, fair value adjustment | $	$ 11.1

Properties Held for Sale and 59

Properties Held for Sale and Property Dispositions (Details) $ in Millions	1 Months Ended
	Jan. 31, 2018USD ($)ft²	Jun. 30, 2018ft²
Properties Sold [Abstract]
Approximate Square Feet | ft²		31,150,063
600 Lexington Ave
Properties Sold [Abstract]
Approximate Square Feet | ft²	303,515
Sales Price	$ 305
Gain on Sale (Loss)	$ 23.8
115-117 Stevens Avenue
Properties Sold [Abstract]
Approximate Square Feet | ft²	178,000
Sales Price	$ 12
Gain on Sale (Loss)	$ (0.7)
635 Madison Avenue
Properties Sold [Abstract]
Approximate Square Feet | ft²	176,530
Sales Price	$ 153
Gain on Sale (Loss)	$ (14.1)

Debt and Preferred Equity Inv60

Debt and Preferred Equity Investments - Additional Information (Details) - USD ($)	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2014
Mortgage Loans on Real Estate [Line Items]
Aggregate weighted average current yield (as a percent)	9.06%
Debt Investments Held [Abstract]
Carrying Value	$ 2,168,515,000	$ 2,114,041,000
Mezzanine/Jr. Mortgage Loan with an Initial Maturity Date of April 2017
Debt Investments Held [Abstract]
Carrying Value	250,500,000	0	$ 0
Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Amount participated out	1,300,000
Mezzanine Loan, with an Initial Maturity Date of June 2024
Debt Investments Held [Abstract]
Amount participated out	12,000,000
Mezzanine Loan with an Initial Maturity Date of December 2018
Debt Investments Held [Abstract]
Amount participated out	14,600,000
Mezzanine Loan with an Initial Maturity Date of December 2018, 2
Debt Investments Held [Abstract]
Amount participated out	14,100,000
Mezzanine Loan with an Initial Maturity of March 2019
Debt Investments Held [Abstract]
Amount participated out	5,100,000
Debt Investments in Mortgage Loans
Debt Investments Held [Abstract]
Future Funding Obligations	222,192,000
Senior Financing	7,150,615,000
Carrying Value	2,023,383,000	1,969,618,000
Total fixed rate
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	3,895,701,000
Carrying Value	424,938,000	669,968,000
Total fixed rate | Mezzanine/Jr. Mortgage Loan with an Initial Maturity Date of April 2017
Debt Investments Held [Abstract]
Interest Receivable	7,700,000
Total fixed rate | Mortgage Loan, February 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	26,394,000	26,366,000
Loan acquired				$ 26,400,000
Discount amount				200,000
Total fixed rate | Mortgage Loan, August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	164,000	239,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,160,000,000
Carrying Value	208,506,000	204,005,000
Total fixed rate | Mezzanine Loan, September 2021
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	15,000,000
Carrying Value	3,500,000	3,500,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of April 2022
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	147,000,000
Carrying Value	24,922,000	24,913,000
Total fixed rate | Mezzanine Loan, November 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	86,201,000
Carrying Value	12,702,000	12,699,000
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of June 2024
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	115,000,000
Carrying Value	12,936,000	12,932,000
Total fixed rate | Mezzanine Loan, January 2025
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	95,000,000
Carrying Value	30,000,000	30,000,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of November 2026
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	340,000,000
Carrying Value	15,000,000	15,000,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of June 2027
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,657,500,000
Carrying Value	55,250,000	55,250,000
Total fixed rate | Real Estate Acquired in Satisfaction of Debt [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	250,464,000
Total fixed rate | Junior Mortgage Participation, Related To Mortgage Loan, February 2019
Debt Investments Held [Abstract]
Loan acquired				5,700,000
Discount amount				$ 5,700,000
Total floating rate
Debt Investments Held [Abstract]
Future Funding Obligations	222,192,000
Senior Financing	3,254,914,000
Carrying Value	1,598,445,000	1,299,650,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Future Funding Obligations	45,019,000
Senior Financing	0
Carrying Value	333,290,000	0
Total floating rate | Mortgage and Mezzanine Loan with an Initial Maturity Date of April 2020 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	6,386,000
Senior Financing	35,912,000
Carrying Value	11,829,000	11,259,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	175,000,000
Carrying Value	37,355,000	37,250,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	61,130,000
Carrying Value	21,718,000	34,947,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of August 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	20,523,000
Carrying Value	10,970,000	10,934,000
Total floating rate | Mortgage/Mezzanine Loan, with an Initial Maturity Date of August 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	19,990,000	19,940,000
Total floating rate | Mezzanine Loan With An Initial Maturity Date of August 2018, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	65,000,000
Carrying Value	14,992,000	14,955,000
Total floating rate | Mortgage/Mezzanine Loan, September 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	16,992,000	16,969,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of September 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	37,500,000
Carrying Value	14,961,000	14,855,000
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of October 2016 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	2,325,000
Senior Financing	45,025,000
Carrying Value	35,072,000	34,879,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of October 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	150,000,000
Carrying Value	15,347,000	15,381,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	14,836,000	14,869,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	33,000,000
Carrying Value	26,967,000	26,927,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 3
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	175,000,000
Carrying Value	59,873,000	59,723,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of December 2018, 4
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	45,000,000
Carrying Value	12,211,000	12,174,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of January 2019
Debt Investments Held [Abstract]
Future Funding Obligations	4,000,000
Senior Financing	29,291,000
Carrying Value	9,980,000	8,550,000
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2019, 2
Debt Investments Held [Abstract]
Future Funding Obligations	795,000
Senior Financing	0
Carrying Value	15,150,000	15,148,000
Total floating rate | Mezzanine Loan with an Initial Maturity of March 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	38,000,000
Carrying Value	21,964,000	21,939,000
Total floating rate | Mezzanine Loan with an Initial Maturity of March 2019, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000,000
Carrying Value	19,958,000	19,982,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	265,000,000
Carrying Value	24,895,000	24,830,000
Total floating rate | Mezzanine Loan with an Initial Maturity Date of April 2019, 2 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	20,065,000
Senior Financing	220,572,000
Carrying Value	79,551,000	71,832,000
Total floating rate | Mortgage/Jr Mortgage Participate Loan, Maturity Date of August 2019
Debt Investments Held [Abstract]
Future Funding Obligations	2,034,000
Senior Financing	189,829,000
Carrying Value	37,884,000	37,851,000
Total floating rate | Mezzanine Loan, Maturity of September 2019
Debt Investments Held [Abstract]
Future Funding Obligations	20,560,000
Senior Financing	0
Carrying Value	168,369,000	143,919,000
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of September 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	350,000,000
Carrying Value	34,810,000	34,737,000
Total floating rate | Mezzanine Loan with an Initial Maturity of October 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	1,306,000
Senior Financing	0
Carrying Value	46,168,000	0
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity Date of December 2019 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	17,627,000
Senior Financing	0
Carrying Value	51,981,000	43,845,000
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	1,123,000
Senior Financing	571,863,000
Carrying Value	78,462,000	75,834,000
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	14,786,000
Senior Financing	0
Carrying Value	84,783,000	0
Total floating rate | Mortgage Loan with an Initial Maturity of February 2020 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	3,878,000
Senior Financing	306,711,000
Carrying Value	50,669,000	0
Total floating rate | Mezzanine Loan with an Initial Maturity of July 2020 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	44,088,000
Senior Financing	340,558,000
Carrying Value	83,065,000	75,428,000
Total floating rate | Mezzanine Loan with an Initial Maturity of July 2020 [Domain]
Debt Investments Held [Abstract]
Future Funding Obligations	38,200,000
Senior Financing	0
Carrying Value	93,498,000	88,989,000
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of December 2020 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	35,207,000	35,152,000
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of December 2020, 2 [Member]
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	60,000,000
Carrying Value	15,648,000	15,635,000
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	0
Carrying Value	0	162,553,000
Total floating rate | Mezzanine Loan with an Initial Maturity of August 2022
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	280,000,000
Carrying Value	35,564,000	34,600,000
Total floating rate | Mortgage/Mezzanine Loan repaid in June 2017
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	74,755,000
Total floating rate | Mezzanine Loan Contributed for a Joint Venture Interest
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	$ 0	$ 23,609,000

Debt and Preferred Equity Inv61

Debt and Preferred Equity Investments - Rollforward of Net Book Balance (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at beginning of period	$ 2,114,041	$ 1,640,412
Redemptions/Sales/Syndications/Amortization	(561,389)	(813,418)
Balance at end of period	2,168,515	2,114,041
Debt Investments in Mortgage Loans
Movement in Mortgage Loans on Real Estate [Roll Forward]
Originations/Accretion	611,686	1,142,591
Preferred equity investments
Movement in Mortgage Loans on Real Estate [Roll Forward]
Originations/Accretion	$ 4,177	$ 144,456

Debt and Preferred Equity Inv62

Debt and Preferred Equity Investments - Preferred Equity Investments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Preferred equity investment
Aggregate weighted average current yield (as a percent)	9.06%
Carrying Value	$ 2,168,515	$ 2,114,041
Preferred Equity, April 2021
Preferred equity investment
Future Funding Obligations	0
Senior Financing	272,000
Carrying Value	$ 145,132	144,423
Preferred equity investments
Preferred equity investment
Aggregate weighted average current yield (as a percent)	5.73%
Future Funding Obligations	$ 0
Senior Financing	272,000
Carrying Value	$ 145,132	$ 144,423

Debt and Preferred Equity Inv63

Debt and Preferred Equity Investments - Narrative (Details)	6 Months Ended		37 Months Ended
	Jun. 30, 2018USD ($)segment	Jun. 30, 2017segment	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Preferred equity investment
Carrying Value	$ 2,168,515,000			$ 2,114,041,000
Number of portfolio segments of financial receivables (segment) | segment	1	1
Additional amount of financing receivables included in other assets	$ 89,600,000			65,500,000
Mezzanine/Jr. Mortgage Loan with an Initial Maturity Date of April 2017
Preferred equity investment
Carrying Value	250,500,000			0	$ 0
Junior Mortgage Participation Acquired in September 2014
Preferred equity investment
Payments to acquire loans			$ 0
Carrying Value	$ 0			$ 0	$ 0

Investments in Unconsolidated64

Investments in Unconsolidated Joint Ventures - Additional Information (Details) $ in Thousands	Jan. 01, 2018USD ($)	Feb. 28, 2018	Nov. 30, 2017	May 31, 2017USD ($)	Oct. 31, 2016	Mar. 31, 2018property	Jun. 30, 2018USD ($)ft²unit	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)ft²unit	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)
General information on each joint venture
Net equity investment in VIEs in which the entity is not primary beneficiary							$ 680,100		$ 680,100		$ 606,200
Unaudited Approximate Square Feet (sqft) | ft²							31,150,063		31,150,063
Purchase price and other fair value adjustments							$ 11,149	$ 0	$ 60,442	$ 0
100 Park Avenue
General information on each joint venture
Ownership Interest							49.90%		49.90%
Unaudited Approximate Square Feet (sqft) | ft²							834,000		834,000
Acquisition Price							$ 95,800		$ 95,800
717 Fifth Avenue
General information on each joint venture
Ownership Interest							10.92%		10.92%
Unaudited Approximate Square Feet (sqft) | ft²							119,500		119,500
Acquisition Price							$ 251,900		$ 251,900
800 Third Avenue
General information on each joint venture
Ownership Interest							60.52%		60.52%
Unaudited Approximate Square Feet (sqft) | ft²							526,000		526,000
Acquisition Price							$ 285,000		$ 285,000
11 West 34th Street
General information on each joint venture
Ownership Interest							30.00%		30.00%
Unaudited Approximate Square Feet (sqft) | ft²							17,150		17,150
Acquisition Price							$ 10,800		$ 10,800
3 Columbus Circle
General information on each joint venture
Ownership Interest							48.90%		48.90%
Unaudited Approximate Square Feet (sqft) | ft²							741,500		741,500
Acquisition Price							$ 500,000		$ 500,000
280 Park Avenue
General information on each joint venture
Ownership Interest							50.00%		50.00%
Unaudited Approximate Square Feet (sqft) | ft²							1,219,158		1,219,158
Acquisition Price							$ 400,000		$ 400,000
1552-1560 Broadway
General information on each joint venture
Ownership Interest							50.00%		50.00%
Unaudited Approximate Square Feet (sqft) | ft²							57,718		57,718
Acquisition Price							$ 136,550		$ 136,550
724 Fifth Avenue
General information on each joint venture
Ownership Interest							50.00%		50.00%
Unaudited Approximate Square Feet (sqft) | ft²							65,010		65,010
Acquisition Price							$ 223,000		$ 223,000
10 East 53rd Street
General information on each joint venture
Ownership Interest							55.00%		55.00%
Unaudited Approximate Square Feet (sqft) | ft²							354,300		354,300
Acquisition Price							$ 252,500		$ 252,500
521 Fifth Avenue
General information on each joint venture
Ownership Interest							50.50%		50.50%
Unaudited Approximate Square Feet (sqft) | ft²							460,000		460,000
Acquisition Price							$ 315,000		$ 315,000
21 East 66th Street
General information on each joint venture
Ownership Interest							32.28%		32.28%
Unaudited Approximate Square Feet (sqft) | ft²							13,069		13,069
Acquisition Price							$ 75,000		$ 75,000
650 Fifth Avenue
General information on each joint venture
Ownership Interest							50.00%		50.00%
Unaudited Approximate Square Feet (sqft) | ft²							69,214		69,214
Acquisition Price							$ 0		$ 0
121 Greene Street
General information on each joint venture
Ownership Interest							50.00%		50.00%
Unaudited Approximate Square Feet (sqft) | ft²							7,131		7,131
Acquisition Price							$ 27,400		$ 27,400
55 West 46th Street
General information on each joint venture
Ownership Interest							25.00%		25.00%
Unaudited Approximate Square Feet (sqft) | ft²							347,000		347,000
Acquisition Price							$ 295,000		$ 295,000
Stonehenge Portfolio
General information on each joint venture
Ownership Interest					90.00%
Unaudited Approximate Square Feet (sqft) | ft²							1,439,016		1,439,016
Acquisition Price							$ 36,668		$ 36,668
Number of properties sold | property						2
131-137 Spring Street
General information on each joint venture
Ownership Interest							20.00%		20.00%
Unaudited Approximate Square Feet (sqft) | ft²							68,342		68,342
Acquisition Price							$ 277,750		$ 277,750
605 West 42nd Street
General information on each joint venture
Ownership Interest							20.00%		20.00%
Unaudited Approximate Square Feet (sqft) | ft²							927,358		927,358
Acquisition Price							$ 759,000		$ 759,000
11 Madison Avenue
General information on each joint venture
Ownership Interest							60.00%		60.00%
Unaudited Approximate Square Feet (sqft) | ft²							2,314,000		2,314,000
Acquisition Price							$ 2,605,000		$ 2,605,000
333 East 22nd St
General information on each joint venture
Ownership Interest							33.33%		33.33%
Economic Interest (as a percent)							33.33%		33.33%
Unaudited Approximate Square Feet (sqft) | ft²							26,926		26,926
Acquisition Price							$ 0		$ 0
East 400 Street 57
General information on each joint venture
Ownership Interest					51.00%		51.00%		51.00%
Unaudited Approximate Square Feet (sqft) | ft²							290,482		290,482
Acquisition Price							$ 170,000		$ 170,000
1552 Broadway
General information on each joint venture
Unaudited Approximate Square Feet (sqft) | ft²							13,045		13,045
One Vanderbilt
General information on each joint venture
Ownership Interest							71.01%		71.01%
Unaudited Approximate Square Feet (sqft) | ft²							0		0
Acquisition Price							$ 3,310,000		$ 3,310,000
Aggregate equity committed by partners							$ 525,000		$ 525,000
Maximum ownership percentage of partners							29.00%		29.00%
Partners' ownership percentage							13.39%		13.39%
Equity method investment, amount sold				$ 10,000
Worldwide Plaza
General information on each joint venture
Ownership Interest							24.35%		24.35%
Economic Interest (as a percent)							24.35%		24.35%
Unaudited Approximate Square Feet (sqft) | ft²							2,048,725		2,048,725
Acquisition Price							$ 1,725,000		$ 1,725,000
1515 Broadway
General information on each joint venture
Ownership Interest							56.87%		56.87%
Economic Interest (as a percent)							56.87%		56.87%
Unaudited Approximate Square Feet (sqft) | ft²							1,750,000		1,750,000
Acquisition Price							$ 1,950,000		$ 1,950,000
Cumulative effect on retained earnings	$ 600,000
East 400 Street 57
General information on each joint venture
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							3228.00%		3228.00%
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							1614.00%		1614.00%
Number of residential units | unit							3		3
Mezzanine Loan
General information on each joint venture
Ownership Interest				33.33%			33.33%		33.33%
Economic Interest (as a percent)							33.33%		33.33%
Unaudited Approximate Square Feet (sqft) | ft²							0		0
Acquisition Price							$ 15,000		$ 15,000
Allianz Real Estate | 1515 Broadway
General information on each joint venture
Ownership percentage in disposed asset		13.00%	30.00%
Joint venture | 100 Park Avenue
General information on each joint venture
Economic Interest (as a percent)							49.90%		49.90%
Joint venture | 717 Fifth Avenue
General information on each joint venture
Economic Interest (as a percent)							10.92%		10.92%
Joint venture | 800 Third Avenue
General information on each joint venture
Economic Interest (as a percent)							60.52%		60.52%
Joint venture | 11 West 34th Street
General information on each joint venture
Economic Interest (as a percent)							30.00%		30.00%
Joint venture | 3 Columbus Circle
General information on each joint venture
Economic Interest (as a percent)							48.90%		48.90%
Joint venture | 280 Park Avenue
General information on each joint venture
Economic Interest (as a percent)							50.00%		50.00%
Joint venture | 1552-1560 Broadway
General information on each joint venture
Economic Interest (as a percent)							50.00%		50.00%
Joint venture | 724 Fifth Avenue
General information on each joint venture
Economic Interest (as a percent)							50.00%		50.00%
Joint venture | 10 East 53rd Street
General information on each joint venture
Economic Interest (as a percent)							55.00%		55.00%
Joint venture | 521 Fifth Avenue
General information on each joint venture
Economic Interest (as a percent)							50.50%		50.50%
Joint venture | 21 East 66th Street
General information on each joint venture
Economic Interest (as a percent)							32.28%		32.28%
Joint venture | 650 Fifth Avenue
General information on each joint venture
Economic Interest (as a percent)							50.00%		50.00%
Joint venture | 121 Greene Street
General information on each joint venture
Economic Interest (as a percent)							50.00%		50.00%
Joint venture | 55 West 46th Street
General information on each joint venture
Economic Interest (as a percent)							25.00%		25.00%
Joint venture | Stonehenge Portfolio
General information on each joint venture
Ownership Interest					10.00%
Joint venture | 131-137 Spring Street
General information on each joint venture
Economic Interest (as a percent)							20.00%		20.00%
Joint venture | 605 West 42nd Street
General information on each joint venture
Economic Interest (as a percent)							20.00%		20.00%
Joint venture | 11 Madison Avenue
General information on each joint venture
Economic Interest (as a percent)							60.00%		60.00%
Joint venture | East 400 Street 57
General information on each joint venture
Economic Interest (as a percent)							41.00%		41.00%
Joint venture | One Vanderbilt
General information on each joint venture
Economic Interest (as a percent)							71.01%		71.01%
Joint venture | 919 Third Avenue
General information on each joint venture
Ownership Interest							51.00%		51.00%
Economic Interest (as a percent)							51.00%		51.00%
Unaudited Approximate Square Feet (sqft) | ft²							1,454,000		1,454,000
Acquisition Price							$ 1,256,727		$ 1,256,727

Investments in Unconsolidated65

Investments in Unconsolidated Joint Ventures - Acquisition, Development and Construction Arrangements/Sale of Joint Venture Interest or Property (Details) - USD ($) $ in Thousands	1 Months Ended					3 Months Ended		6 Months Ended
	Jun. 30, 2018	May 31, 2018	Apr. 30, 2018	Mar. 31, 2018	Feb. 28, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Oct. 31, 2016
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 3,059,985					$ 3,059,985		$ 3,059,985		$ 2,362,989
Equity in net gain on sale of interest in unconsolidated joint venture/real estate						72,025	$ 13,089	65,585	$ 15,136
Stonehenge Portfolio
Schedule of Equity Method Investments [Line Items]
Ownership Interest											90.00%
Preferred Equity due September 2018
Schedule of Equity Method Investments [Line Items]
Equity method investments	141,000					141,000		141,000		0
Mezzanine loan due February 2022
Schedule of Equity Method Investments [Line Items]
Equity method investments	44,483					44,483		44,483		44,823
Mezzanine loan due July 2036
Schedule of Equity Method Investments [Line Items]
Equity method investments	28,105					28,105		28,105		26,716
Mezzanine Loan and Preferred Equity, Due March 2018
Schedule of Equity Method Investments [Line Items]
Equity method investments	0					0		0		100,000
Mezzanine Loans And Preferred Equity [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 213,588					$ 213,588		$ 213,588		$ 171,539
1274 Fifth Avenue
Schedule of Equity Method Investments [Line Items]
Ownership Interest					9.83%
Gross Asset Valuation					$ 44,100
Equity in net gain on sale of interest in unconsolidated joint venture/real estate					$ (362)
1515 Broadway
Schedule of Equity Method Investments [Line Items]
Ownership Interest					13.00%
Gross Asset Valuation					$ 1,950,000
Equity in net gain on sale of interest in unconsolidated joint venture/real estate					$ 0
Stonehenge Portfolio
Schedule of Equity Method Investments [Line Items]
Ownership Interest				5.00%
Gross Asset Valuation				$ 287,000
Equity in net gain on sale of interest in unconsolidated joint venture/real estate				$ (5,701)
175-225 Third Street Brooklyn, New York
Schedule of Equity Method Investments [Line Items]
Ownership Interest			95.00%
Gross Asset Valuation			$ 115,000
Equity in net gain on sale of interest in unconsolidated joint venture/real estate			$ 19,483
1745 Broadway
Schedule of Equity Method Investments [Line Items]
Ownership Interest		56.87%
Gross Asset Valuation		$ 633,000
Equity in net gain on sale of interest in unconsolidated joint venture/real estate		$ 52,038
Jericho Plaza
Schedule of Equity Method Investments [Line Items]
Ownership Interest	11.67%					11.67%		11.67%
Gross Asset Valuation	$ 117,400					$ 117,400		$ 117,400
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	$ 147

Investments in Unconsolidated66

Investments in Unconsolidated Joint Ventures - Mortgages and Other Loans Payable (Details)	6 Months Ended
	Jun. 30, 2018USD ($)extension	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Total fixed rate debt	$ 1,861,696,000	$ 2,400,560,000
Total floating rate debt	677,000,000	465,431,000
Total fixed rate and floating rate debt	2,538,696,000	2,865,991,000
919 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 0	500,000,000
1515 Broadway
Debt Instrument [Line Items]
Economic Interest (as a percent)	56.87%
Worldwide Plaza
Debt Instrument [Line Items]
Economic Interest (as a percent)	24.35%
Joint venture
Debt Instrument [Line Items]
Total fixed rate debt	$ 6,026,624,000	5,569,138,000
Total floating rate debt	3,518,038,000	3,979,066,000
Total fixed rate and floating rate debt	9,544,662,000	9,548,204,000
Deferred financing costs, net	(110,924,000)	(136,103,000)
Total joint venture mortgages and other loans payable, net	$ 9,433,738,000	9,412,101,000
Joint venture | 521 Fifth Avenue
Debt Instrument [Line Items]
Economic Interest (as a percent)	50.50%
Interest rate, fixed rate debt (as a percent)	3.73%
Total fixed rate debt	$ 170,000,000	170,000,000
Joint venture | 717 Fifth Avenue
Debt Instrument [Line Items]
Economic Interest (as a percent)	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]
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 | 650 Fifth Avenue
Debt Instrument [Line Items]
Economic Interest (as a percent)	50.00%
Joint venture | 650 Fifth Avenue | Mortgage loan
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.46%
Total fixed rate debt	$ 210,000,000	210,000,000
Long-term debt, carrying value	$ 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 | 21 East 66th Street
Debt Instrument [Line Items]
Economic Interest (as a percent)	32.28%
Interest rate, fixed rate debt (as a percent)	3.60%
Interest rate, floating rate debt (as a percent)	2.75%
Total fixed rate debt	$ 12,000,000	12,000,000
Total floating rate debt	$ 1,608,000	1,648,000
Joint venture | 919 Third Avenue
Debt Instrument [Line Items]
Economic Interest (as a percent)	51.00%
Interest rate, fixed rate debt (as a percent)	5.12%
Total fixed rate debt	$ 500,000,000	0
Joint venture | 3 Columbus Circle
Debt Instrument [Line Items]
Economic Interest (as a percent)	48.90%
Interest rate, fixed rate debt (as a percent)	3.61%
Total fixed rate debt	$ 350,000,000	350,000,000
Joint venture | 1515 Broadway
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.93%
Total fixed rate debt	$ 864,238,000	872,528,000
Joint venture | 11 Madison Avenue
Debt Instrument [Line Items]
Economic Interest (as a 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
Joint venture | 800 Third Avenue
Debt Instrument [Line Items]
Economic Interest (as a percent)	60.52%
Interest rate, fixed rate debt (as a percent)	3.37%
Total fixed rate debt	$ 177,000,000	177,000,000
Joint venture | East 400 Street 57
Debt Instrument [Line Items]
Economic Interest (as a percent)	41.00%
Interest rate, fixed rate debt (as a percent)	3.00%
Total fixed rate debt	$ 100,000,000	100,000,000
Joint venture | Worldwide Plaza
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.98%
Total fixed rate debt	$ 1,200,000,000	1,200,000,000
Joint venture | Stonehenge Portfolio
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.20%
Interest rate, floating rate debt (as a percent)	1.40%
Total fixed rate debt	$ 323,058,000	357,282,000
Total floating rate debt	38,000,000	55,340,000
Joint venture | 1745 Broadway
Debt Instrument [Line Items]
Total floating rate debt	$ 0	345,000,000
Joint venture | 55 West 46th Street
Debt Instrument [Line Items]
Economic Interest (as a percent)	25.00%
Interest rate, floating rate debt (as a percent)	2.13%
Total floating rate debt	$ 174,430,000	171,444,000
Committed amount	195,000,000
Unused borrowing capacity, amount	20,600,000
Joint venture | 175-225 Third Street Brooklyn, New York
Debt Instrument [Line Items]
Total floating rate debt	0	40,000,000
Joint venture | Jericho Plaza
Debt Instrument [Line Items]
Total floating rate debt	$ 0	81,099,000
Joint venture | 724 Fifth Avenue
Debt Instrument [Line Items]
Economic Interest (as a percent)	50.00%
Interest rate, floating rate debt (as a percent)	2.42%
Total floating rate debt	$ 275,000,000	275,000,000
Joint venture | 1552 Broadway
Debt Instrument [Line Items]
Economic Interest (as a percent)	50.00%
Interest rate, floating rate debt (as a percent)	2.65%
Total floating rate debt	$ 195,000,000	195,000,000
Joint venture | 280 Park Avenue
Debt Instrument [Line Items]
Economic Interest (as a 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
Joint venture | 121 Greene Street
Debt Instrument [Line Items]
Economic Interest (as a percent)	50.00%
Interest rate, floating rate debt (as a percent)	1.50%
Total floating rate debt	$ 15,000,000	15,000,000
Joint venture | 10 East 53rd Street
Debt Instrument [Line Items]
Economic Interest (as a percent)	55.00%
Interest rate, floating rate debt (as a percent)	2.25%
Total floating rate debt	$ 170,000,000	170,000,000
Joint venture | 131-137 Spring Street
Debt Instrument [Line Items]
Economic Interest (as a percent)	20.00%
Interest rate, floating rate debt (as a percent)	1.55%
Total floating rate debt	$ 141,000,000	141,000,000
Joint venture | 11 West 34th Street
Debt Instrument [Line Items]
Economic Interest (as a percent)	30.00%
Interest rate, floating rate debt (as a percent)	1.45%
Total floating rate debt	$ 23,000,000	23,000,000
Joint venture | 100 Park Avenue
Debt Instrument [Line Items]
Economic Interest (as a percent)	49.90%
Interest rate, floating rate debt (as a percent)	1.75%
Total floating rate debt	$ 360,000,000	360,000,000
Joint venture | One Vanderbilt
Debt Instrument [Line Items]
Economic Interest (as a percent)	71.01%
Interest rate, floating rate debt (as a percent)	3.50%
Total floating rate debt	$ 375,000,000	355,535,000
Joint venture | One Vanderbilt | Construction Loans
Debt Instrument [Line Items]
Maximum facility capacity	$ 1,500,000,000
Credit facility, interest rate (as a percent)	3.50%
Term (in Years)	5 years
Number of extension options | extension	2
Period of extension options	1 year
Joint venture | 605 West 42nd Street
Debt Instrument [Line Items]
Economic Interest (as a percent)	20.00%
Interest rate, floating rate debt (as a percent)	1.44%
Total floating rate debt	$ 550,000,000	$ 550,000,000
Mezzanine Loan, Initial Maturity October 2022 [Member] | Joint venture | 650 Fifth Avenue | Mezzanine loans
Debt Instrument [Line Items]
Long-term debt, carrying value	65,000,000
Secured Debt, Initial Maturity August 2019 | Joint venture | Stonehenge Portfolio
Debt Instrument [Line Items]
Total fixed rate debt	135,700,000
Secured Debt, Initial Maturity June 2024 | Joint venture | Stonehenge Portfolio
Debt Instrument [Line Items]
Total fixed rate debt	54,800,000
Secured Debt, Initial Maturity April 2028 | Joint venture | Stonehenge Portfolio
Debt Instrument [Line Items]
Total fixed rate debt	$ 132,600,000

Investments in Unconsolidated67

Investments in Unconsolidated Joint Ventures - Schedules of Combined Financial Statements for the Unconsolidated Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Assets (1)
Commercial real estate property, net	$ 6,595,221		$ 6,595,221		$ 7,906,006
Cash and cash equivalents	287,240	$ 270,965	287,240	$ 270,965	127,888
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	47,482		47,482		57,644
Other assets	290,729		290,729		310,688
Liabilities and equity (1)
Mortgages and other loans payable, net	2,517,097		2,517,097		2,837,282
Deferred revenue/gain	95,756		95,756		208,119
Other liabilities	108,151		108,151		188,005
Company's investments in unconsolidated joint ventures	3,059,985		3,059,985		2,362,989
Combined statements of income for the unconsolidated joint ventures
Operating expenses	56,237	70,852	116,019	145,358
Ground rent	8,846	8,308	17,154	16,616
Real estate taxes	45,322	60,945	90,983	122,013
Interest expense, net of interest income	53,611	64,856	101,527	130,478
Amortization of deferred financing costs	3,546	3,432	7,083	8,193
Transaction related costs	348	46	510	179
Depreciation and amortization	67,914	133,054	137,302	227,188
Total expenses	258,303	365,749	516,585	698,424
Company's equity in net income from unconsolidated joint ventures (1)	4,702	3,412	8,738	10,026
Joint venture
Investment in Unconsolidated Joint Ventures
Management fees, base revenue	3,000	12,400	6,900	17,900
Assets (1)
Commercial real estate property, net	14,193,325		14,193,325		12,822,133
Cash and cash equivalents	434,307		434,307		494,909
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	308,653		308,653		349,944
Debt and preferred equity investments, net	228,588		228,588		202,539
Other assets	2,254,990		2,254,990		1,407,806
Total assets	17,419,863		17,419,863		15,277,331
Liabilities and equity (1)
Mortgages and other loans payable, net	9,433,738		9,433,738		9,412,101
Deferred revenue/gain	1,863,384		1,863,384		985,648
Other liabilities	478,916		478,916		411,053
Equity	5,643,825		5,643,825		4,468,529
Total liabilities and equity	17,419,863		17,419,863		15,277,331
Company's investments in unconsolidated joint ventures	3,059,985		3,059,985		$ 2,362,989
Combined statements of income for the unconsolidated joint ventures
Total revenues	314,195	210,590	635,136	427,109
Operating expenses	50,356	39,147	110,129	77,941
Ground rent	4,457	4,179	8,850	8,430
Real estate taxes	55,838	35,170	112,865	70,109
Interest expense, net of interest income	91,648	59,702	181,389	115,030
Amortization of deferred financing costs	7,350	7,458	12,466	13,963
Transaction related costs	0	56	0	146
Depreciation and amortization	111,495	65,944	216,575	137,109
Total expenses	321,144	211,656	642,274	422,728
Net (loss) income before gain on sale (1)	(6,949)	(1,066)	(7,138)	4,381
Company's equity in net income from unconsolidated joint ventures (1)	$ 4,702	$ 3,412	$ 8,738	$ 10,026

Deferred Costs (Details)

Deferred Costs (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred leasing costs	$ 426,875	$ 443,341
Less: accumulated amortization	(227,934)	(217,140)
Deferred costs, net	$ 198,941	$ 226,201

Mortgages and Other Loans Pay69

Mortgages and Other Loans Payable (Details)	6 Months Ended
	Jun. 30, 2018USD ($)extensiondebt_instrument	Apr. 30, 2018USD ($)	Dec. 31, 2017USD ($)	Jul. 31, 2016USD ($)
Debt Instrument [Line Items]
Total fixed rate debt	$ 1,861,696,000		$ 2,400,560,000
Total floating rate debt	677,000,000		465,431,000
Total fixed rate and floating rate debt	2,538,696,000		2,865,991,000
Mortgages reclassed to liabilities related to assets held for sale	0		0
Total mortgages and other loans payable	2,538,696,000		2,865,991,000
Deferred financing costs, net of amortization	(21,599,000)		(28,709,000)
Total mortgages and other loans payable, net	2,517,097,000		2,837,282,000
Book value of collateral	3,800,000,000		4,800,000,000
Outstanding under line of credit facility	351,272,000		30,336,000
Series J Preferred Units
Debt Instrument [Line Items]
Total fixed rate debt	0		4,000,000
Unsecured Loan
Debt Instrument [Line Items]
Total fixed rate debt	$ 0		16,000,000
Uncommitted Master Repurchase Agreements
Debt Instrument [Line Items]
Number of debt instruments | debt_instrument	2
Uncommitted Master Repurchase Agreement 2017
Debt Instrument [Line Items]
Total floating rate debt	$ 300,000,000		90,809,000
Term (in Years)	1 year
Maximum facility capacity	$ 300,000,000	$ 400,000,000
Number of extension options | extension	2
Period of extension options	1 year
Extension option exercised, term	1 year
Outstanding under line of credit facility	$ 299,200,000
Uncommitted Master Repurchase Agreement 2017 | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.34%
Uncommitted Master Repurchase Agreement 2016
Debt Instrument [Line Items]
Term (in Years)	2 years
Maximum facility capacity				$ 300,000,000
Period of extension options	1 year
Basis point fee (as a percent)	0.25%
Threshold amount for basis point fee to be applicable (less than)	$ 150,000,000
Uncommitted Master Repurchase Agreement 2016 | Minimum | LIBOR
Debt Instrument [Line Items]
Credit facility, interest rate (as a percent)	2.25%
Uncommitted Master Repurchase Agreement 2016 | Maximum | LIBOR
Debt Instrument [Line Items]
Credit facility, interest rate (as a percent)	4.00%
One Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 469,564,000		486,153,000
One Madison Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.91%
762 Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 771,000		771,000
762 Madison Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.00%
100 Church Street
Debt Instrument [Line Items]
Total fixed rate debt	$ 215,223,000		217,273,000
100 Church Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.68%
420 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 300,000,000		300,000,000
420 Lexington Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.99%
400 East 58th Street
Debt Instrument [Line Items]
Total fixed rate debt	$ 40,000,000		40,000,000
400 East 58th Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.00%
Term (in Years)	5 years
Landmark Square
Debt Instrument [Line Items]
Total fixed rate debt	$ 100,000,000		100,000,000
Landmark Square | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.90%
485 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 450,000,000		450,000,000
485 Lexington Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.25%
1080 Amsterdam Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 36,138,000		36,363,000
Total fixed rate debt	35,500,000
Subordinate loan	$ 900,000
1080 Amsterdam Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.58%
Term (in Years)	5 years
1080 Amsterdam Avenue | Mortgage loan | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.50%
1080 Amsterdam Avenue | Subordinate loan | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	7.00%
315 West 33rd Street
Debt Instrument [Line Items]
Total fixed rate debt	$ 250,000,000		250,000,000
315 West 33rd Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.17%
919 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 0		500,000,000
919 Third Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)
719 Seventh Avenue
Debt Instrument [Line Items]
Total floating rate debt	$ 44,000,000		41,622,000
719 Seventh Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	3.05%
183, 187 Broadway & 5-7 Dey Street (7)
Debt Instrument [Line Items]
Total floating rate debt	$ 58,000,000		58,000,000
183, 187 Broadway & 5-7 Dey Street (7) | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.70%
220 East 42nd Street
Debt Instrument [Line Items]
Total floating rate debt	$ 275,000,000		$ 275,000,000
220 East 42nd Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.60%

Corporate Indebtedness - Additi

Corporate Indebtedness - Additional Information (Details)	Aug. 07, 2018USD ($)	Jun. 30, 2018USD ($)extension	Dec. 31, 2017USD ($)
Corporate Indebtedness
Outstanding under line of credit facility		$ 351,272,000	$ 30,336,000
Term Loan B, Maturity November 21, 2024 | Term loan
Corporate Indebtedness
Credit facility, maximum borrowing capacity		$ 200,000,000
Term Loan B, Maturity November 21, 2024 | LIBOR | Term loan
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.65%
Term Loan B, Maturity November 21, 2024 | LIBOR | Minimum | Term loan
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.50%
Term Loan B, Maturity November 21, 2024 | LIBOR | Maximum | Term loan
Corporate Indebtedness
Interest rate added to base rate (as a percent)		2.45%
Revolving credit facility
Corporate Indebtedness
Facility fee (as a percent)		0.20%
Outstanding under line of credit facility		$ 360,000,000
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%
Term loan
Corporate Indebtedness
Credit facility, maximum borrowing capacity		$ 1,500,000,000
Term loan | Line of Credit
Corporate Indebtedness
Long-term debt, carrying value		1,500,000,000	1,500,000,000
2012 Credit Facility
Corporate Indebtedness
Letters of credit		11,800,000
Ability to borrow under line of credit facility		1,100,000,000
2012 Credit Facility | Line of Credit
Corporate Indebtedness
Long-term debt, carrying value		351,300,000	$ 30,300,000
Term Loan A, Maturity March 31, 2023 | Term loan
Corporate Indebtedness
Credit facility, maximum borrowing capacity		$ 1,300,000,000
Term Loan A, Maturity March 31, 2023 | LIBOR | Term loan
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.10%
Term Loan A, Maturity March 31, 2023 | LIBOR | Minimum | Term loan
Corporate Indebtedness
Interest rate added to base rate (as a percent)		0.90%
Term Loan A, Maturity March 31, 2023 | LIBOR | Maximum | Term loan
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.75%
Revolving credit facility | Revolving Credit Facility, Maturity March 31, 2022 | Line of Credit
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 | Revolving Credit Facility, Maturity March 31, 2022 | LIBOR | Line of Credit
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.00%
Revolving credit facility | Revolving Credit Facility, Maturity March 31, 2022 | LIBOR | Minimum | Line of Credit
Corporate Indebtedness
Interest rate added to base rate (as a percent)		0.825%
Revolving credit facility | Revolving Credit Facility, Maturity March 31, 2022 | LIBOR | Maximum | Line of Credit
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.55%
Subsequent Event | Senior Unsecured Notes Due August 2021 | Senior Unsecured Notes
Corporate Indebtedness
Face amount of loan	$ 350,000,000
Interest rate added to base rate (as a percent)	0.98%

Corporate Indebtedness - Senior

Corporate Indebtedness - Senior Unsecured Notes (Details) - USD ($)	1 Months Ended	6 Months Ended
	Oct. 31, 2017	Jun. 30, 2018	Dec. 31, 2017
Debt disclosures by scheduled maturity date
Accreted Balance		$ 1,492,320,000	$ 1,491,575,000
Senior unsecured notes
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		1,400,000,000
Accreted Balance		1,404,203,000	1,404,605,000
Deferred financing costs, net		(7,481,000)	(8,666,000)
Accreted Balance, net of deferred financing costs		1,396,722,000	1,395,939,000
Senior unsecured notes | 5.00% Senior unsecured notes maturing on August 15, 2018
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		250,000,000
Accreted Balance		$ 249,991,000	249,953,000
Coupon Rate (as a percent)		5.00%
Initial Term (in Years)		7 years
Senior unsecured notes | 7.75% Senior unsecured notes maturing on March 15, 2020
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 250,000,000
Accreted Balance		$ 250,000,000	250,000,000
Coupon Rate (as a percent)		7.75%
Initial Term (in Years)		10 years
Senior unsecured notes | 4.50% Senior unsecured notes maturing on December 1, 2022
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 300,000,000
Accreted Balance		$ 304,673,000	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
Senior unsecured notes | 3.25 Percent Senior Unsecured Notes Due October 2022
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 500,000,000
Accreted Balance		$ 499,539,000	$ 499,489,000
Coupon Rate (as a percent)		3.25%
Initial Term (in Years)		5 years
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%

Corporate Indebtedness - Junior

Corporate Indebtedness - Junior Subordinated Deferrable Interest Debentures and Principal Maturities (Details) - USD ($)	1 Months Ended	6 Months Ended
	Jun. 30, 2005	Jun. 30, 2018
Principal Repayments and Joint Venture Debt
Remaining 2,018		$ 269,097,000
2,019		144,271,000
2,020		1,252,997,000
2,021		11,638,000
2,022		1,007,985,000
Thereafter		3,212,708,000
Total principal repayments		$ 5,898,696,000
Trust Preferred Securities
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 100,000,000
LIBOR | Trust Preferred Securities
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)		1.25%
Joint venture
Principal Repayments and Joint Venture Debt
Remaining 2,018		$ 4,986,000
2,019		252,795,000
2,020		276,006,000
2,021		454,621,000
2,022		220,810,000
Thereafter		2,879,344,000
Total principal repayments		4,088,562,000
Joint venture | Trust Preferred Securities
Principal Repayments and Joint Venture Debt
Remaining 2,018		0
2,019		0
2,020		0
2,021		0
2,022		0
Thereafter		100,000,000
Total principal repayments		100,000,000
Joint venture | Mortgages and other loans payable
Scheduled Amortization
Remaining 2,018		19,097,000
2,019		42,271,000
2,020		23,466,000
2,021		11,638,000
2,022		9,430,000
Thereafter		16,591,000
Total amortization of debt		122,493,000
Principal Repayments and Joint Venture Debt
Remaining 2,018		0
2,019		102,000,000
2,020		979,531,000
2,021		0
2,022		198,555,000
Thereafter		1,136,117,000
Total principal repayments		2,416,203,000
Joint venture | Revolving Credit Facility
Principal Repayments and Joint Venture Debt
Remaining 2,018		0
2,019		0
2,020		0
2,021		0
2,022		0
Thereafter		360,000,000
Total principal repayments		360,000,000
Joint venture | Unsecured Term Loans
Principal Repayments and Joint Venture Debt
Remaining 2,018		0
2,019		0
2,020		0
2,021		0
2,022		0
Thereafter		1,500,000,000
Total principal repayments		1,500,000,000
Joint venture | Senior Unsecured Notes
Principal Repayments and Joint Venture Debt
Remaining 2,018		250,000,000
2,019		0
2,020		250,000,000
2,021		0
2,022		800,000,000
Thereafter		100,000,000
Total principal repayments		$ 1,400,000,000

Corporate Indebtedness - Schedu

Corporate Indebtedness - Schedule of Consolidated Interest Expense, Excluding Capitalized Interest (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest expense
Interest expense before capitalized interest	$ 61,553	$ 71,992	$ 116,471	$ 144,414
Interest capitalized	(7,594)	(6,743)	(14,280)	(13,022)
Interest income	(348)	(393)	(664)	(914)
Interest expense, net	$ 53,611	$ 64,856	$ 101,527	$ 130,478

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Dec. 31, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Amounts due from/to related parties
Due from joint ventures		$ 17,446		$ 17,446		$ 15,025
Other		10,408		10,408		8,014
Related party receivables		27,854		27,854		$ 23,039
Alliance Building Services
Related Party Transactions
Profit participation from related party		1,000	$ 1,000	2,000	$ 2,000
Payments made for services		5,100	5,800	9,100	10,300
Entity with Stephen L Green ownership interest
Related Party Transactions
Property management fees from related party		100	$ 100	300	$ 300
One Vanderbilt | Marc Holliday
Related Party Transactions
Due from related party		1,400		1,400
One Vanderbilt | Andrew Mathias
Related Party Transactions
Due from related party		$ 1,000		$ 1,000
One Vanderbilt | Minimum | Marc Holliday
Related Party Transactions
Percentage of profits due to investors (as a percentage)	1.50%
One Vanderbilt | Minimum | Andrew Mathias
Related Party Transactions
Percentage of profits due to investors (as a percentage)	1.00%
One Vanderbilt | Maximum | Marc Holliday
Related Party Transactions
Percentage of profits due to investors (as a percentage)	1.80%
One Vanderbilt | Maximum | Andrew Mathias
Related Party Transactions
Percentage of profits due to investors (as a percentage)	1.20%

Noncontrolling Interests on t75

Noncontrolling Interests on the Company's Consolidated Financial Statements - Additional Information (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018USD ($)shares$ / shares	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)shares$ / shares	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)shares	Jun. 30, 2016shares	Aug. 31, 2015shares	Jul. 31, 2015shares	Jun. 30, 2015shares	Feb. 28, 2015shares	Aug. 31, 2014shares
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $			$ 461,954,000
Net income | $	$ 5,586,000	$ 419,000	10,858,000	$ 895,000
Accumulated other comprehensive income allocation | $	245,000	(100,000)	864,000	(299,000)
Balance at end of period | $	$ 486,610,000		$ 486,610,000		$ 461,954,000
Number of company common stock issued on conversion of Series B preferred units			6.71348
SL Green Operating Partnership
Organization
Noncontrolling interest in the operating partnership (as a percent)	5.20%		5.20%		4.58%
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares) | shares	4,699,872		4,699,872		4,452,979
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	4,699,872		4,699,872
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	$ 473,882,000
Distributions | $			(7,712,000)		(14,266,000)
Issuance of common units | $			17,714,000		25,723,000
Redemption of common units | $			(1,561,000)		(21,574,000)
Net income | $			10,858,000		3,995,000
Accumulated other comprehensive income allocation | $	$ 245,000	$ (100,000)	864,000	$ (299,000)	(94,000)
Fair value adjustment | $			4,493,000		(5,712,000)
Balance at end of period | $	$ 486,610,000		$ 486,610,000		$ 461,954,000
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) | shares	1,902,000		1,902,000
Dividend rate preferred units (as a percent)			4.50%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			1.125
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 88.50		$ 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) | shares	60		60
Mandatory liquidation preference (in dollars per share) | $	$ 1,000		$ 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) | shares											563,954
Dividend rate preferred units (as a percent)			3.50%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			0.875
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 134.67		$ 134.67
Preferred units, shares authorized (in shares) | shares	700,000		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) | shares											378,634
Dividend rate preferred units (as a percent)			4.00%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			$ 1
Preferred units, shares authorized (in shares) | shares	500,000		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) | shares										1,600,000
Dividend rate preferred units (as a percent)			3.75%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			$ 0.9375
Preferred units, shares authorized (in shares) | shares	1,600,000		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) | shares									552,303
Dividend rate preferred units (as a percent)			3.00%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			$ 0.75
Preferred units, shares authorized (in shares) | shares	552,303		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 (in shares) | shares	1		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) | shares	200,000		200,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares								200,000
Dividend rate preferred units (as a percent)			4.00%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			$ 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) | shares	268,000		268,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares								268,000
Dividend rate preferred units (as a percent)			3.50%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			0.875
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 148.95		$ 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) | shares	400,000		400,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares							400,000
Dividend rate preferred units (as a percent)			3.50%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			0.875
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 154.89		$ 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) | shares	1,077,280		1,077,280
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares							1,077,280
Dividend rate preferred units (as a percent)			4.00%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			$ 1
SL Green Operating Partnership | Series T Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	230,000		230,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares						230,000
Dividend rate preferred units (as a percent)			2.75%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			0.6875
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 119.02		$ 119.02
SL Green Operating Partnership | Series U Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	680,000		680,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares						680,000
Dividend rate preferred units (as a percent)			4.50%
Liquidation preference of preferred units (in dollars per share)	$ 25		$ 25
Annual dividends on preferred units (in dollars per share)			1.125
SL Green Operating Partnership | Series U Preferred Units | Minimum
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Annual dividends on preferred units (in dollars per share)			$ 0.75
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) | shares	109,161		109,161
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares							109,161
Dividend rate preferred units (as a percent)			3.50%
Liquidation preference of preferred units (in dollars per share)	$ 1,000		$ 1,000
Annual dividends on preferred units (in dollars per share)			$ 35
SL Green Operating Partnership | Series B Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares	0		0

Noncontrolling Interests on t76

Noncontrolling Interests on the Company's Consolidated Financial Statements - Common Unit Activity (Details) - SL Green Operating Partnership - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Rollforward Analysis of Preferred Unit Activity
Issuance of preferred units	$ 17,714	$ 25,723
Redemption of preferred units	(1,561)	(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	(350)	(275)
Balance at end of period	$ 301,385	$ 301,735

Stockholders' Equity of the C77

Stockholders' Equity of the Company - Additional Information (Details)	1 Months Ended	3 Months Ended		6 Months Ended	12 Months Ended
	Mar. 31, 2018USD ($)shares	Jun. 30, 2018USD ($)$ / sharesshares	Mar. 31, 2018USD ($)$ / sharesshares	Jun. 30, 2018USD ($)increase$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Aug. 31, 2016USD ($)
Equity, Class of Treasury Stock [Line Items]
Authorized capital stock (shares)		260,000,000		260,000,000
Authorized shares, par value (in dollars per share) | $ / shares		$ 0.01		$ 0.01
Common stock, shares authorized (in shares)		160,000,000		160,000,000	160,000,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.01		$ 0.01	$ 0.01
Excess stock, shares authorized (shares)		75,000,000		75,000,000
Excess stock, par value (in dollars per share) | $ / shares		$ 0.01		$ 0.01
Preferred stock, shares authorized (shares)		25,000,000		25,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.01		$ 0.01
Excess shares issued (shares)		0		0
Shares repurchased		3,479,552	3,653,928		8,342,411
Average price paid per share (in dollars per share) | $ / shares		$ 97.22	$ 97.07		$ 101.64
2016 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount | $		$ 500,000,000		$ 500,000,000	$ 500,000,000	$ 1,000,000,000
Number of increases to share repurchase program | increase				2
Shares repurchased		15,475,891	11,996,339		8,342,411
Maximum approximate dollar value of shares that may yet be purchased under the plan | $	$ 797,200,000	$ 458,900,000	$ 797,200,000	$ 458,900,000	$ 1,152,000,000
Stock repurchase program, authorized amount | $		$ 2,000,000,000		$ 2,000,000,000
Repurchases of common stock (in shares)	101,421

Stockholders' Equity of the C78

Stockholders' Equity of the Company - Perpetual Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	6 Months Ended
	Aug. 31, 2012	Jun. 30, 2018	Dec. 31, 2017	Feb. 28, 2015
Stockholders' Equity
Common stock, shares authorized (in shares)		160,000,000	160,000,000
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%
Perpetual preferred stock, liquidation preference (in dollars per share)		$ 25	$ 25
Perpetual preferred stock, annual dividends per share (in dollars per share)		$ 1.625
Contributions of net proceeds from sale of preferred stock	$ 221.9
Dividend Reinvestment and Stock Purchase Plan (DRIP)
Stockholders' Equity
Common stock, shares authorized (in shares)				3,500,000

Stockholders' Equity of the C79

Stockholders' Equity of the Company - Schedule of Common Stock Issued and Proceeds Received Dividend Reinvestments (Details) - Dividend Reinvestment and Stock Purchase Plan (DRIP) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Stockholders' Equity
Issuance of common stock (in shares)	674	1,036
Dividend reinvestments/stock purchases under the DRSPP	$ 64	$ 111

Stockholders' Equity of the C80

Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic Earnings:
Income attributable to SL Green common stockholders	$ 103,556	$ 8,222	$ 205,322	$ 19,573
Diluted Earnings:
Income attributable to SL Green common stockholders	$ 109,142	$ 8,641	$ 216,180	$ 20,468
Basic Shares:
Weighted average common shares outstanding (shares)	87,176,000	99,900,000	88,772,000	100,268,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (shares)	4,706,000	4,562,000	4,695,000	4,584,000
Stock-based compensation plans (shares)	201,000	270,000	200,000	288,000
Diluted weighted average common stock outstanding (shares)	92,083,000	104,732,000	93,667,000	105,140,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,158,317		1,184,735
Common Stock
Effect of Dilutive Securities:
Redemption of units to common shares	$ 5,586	$ 419	$ 10,858	$ 895

Partners' Capital of the Oper81

Partners' Capital of the Operating Partnership - Additional Information (Details)	6 Months Ended
	Jun. 30, 2018shares	Dec. 31, 2017shares
Common Stock
Stockholders' Equity
Units outstanding (units)	85,725,000	92,803,000
SL Green Operating Partnership
Stockholders' Equity
Noncontrolling interest in the operating partnership (as a percent)	5.20%	4.58%
Number of units of operating partnership owned by the noncontrolling interest unit holders (units)	4,699,872	4,452,979
SL Green Operating Partnership | Series I Preferred Units
Stockholders' Equity
Units outstanding (units)	9,200,000
Period of restriction to redeem OP Units	1 year
Conversion of stock, shares issued	1
SL Green Operating Partnership | Common Stock
Stockholders' Equity
Units outstanding (units)	85,725,135

Partners' Capital of the Oper82

Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Denominator
Weighted average common shares outstanding (shares)	87,176,000	99,900,000	88,772,000	100,268,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,158,317		1,184,735
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 109,142	$ 8,641	$ 216,180	$ 20,468
Denominator
Weighted average common shares outstanding (shares)	91,882,000	104,462,000	93,467,000	104,852,000
Stock-based compensation plans (shares)	201,000	270,000	200,000	288,000
Diluted weighted average common units outstanding (shares)	92,083,000	104,732,000	93,667,000	105,140,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,158,317	986,390	1,184,735	979,676

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Details) $ / shares in Units, fungible_unit in Millions	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Aug. 31, 2014shares	Jun. 30, 2018USD ($)unit / sharesunitfungible_unitshares	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)unit / sharesunitfungible_unit$ / sharesshares	Jun. 30, 2017USD ($)shares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016shares	Jan. 01, 2008shares
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		$ 1,600,000	$ 2,000,000	$ 3,200,000	$ 3,600,000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
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 2 months
Remaining average contractual life of the options exercisable (in years)				3 years 2 months 15 days
Total unrecognized compensation cost related to unvested stock awards		$ 4,900,000		$ 4,900,000
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)				1 year 3 months
Weighted average fair value of options granted during the period				$ 84,068		$ 3,816,652
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
Class O LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award, Preferred Unit Distributions as a Percentage of Common Unit Distributions		10.00%		10.00%
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense				$ 6,251,350	9,809,749
Total unrecognized compensation cost related to unvested stock awards		$ 15,200,000		$ 15,200,000
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)				1 year 10 months
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%
Fair value of restricted stock vested during the period				$ 9,800,000		$ 9,400,000
Weighted average fair value of options granted during the period				$ 163,831	$ 9,905,986
Awards granted (in shares) | shares				1,700	96,185
Awards outstanding (in shares) | shares		3,291,616		3,291,616		3,298,216	3,202,031
LTIP units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of options granted during the period				$ 20,600,000		$ 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		$ 7,500,000		$ 7,500,000
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)				1 year 1 month
Share-based compensation		$ 2,300,000	2,600,000	$ 9,100,000	$ 12,600,000
Third Amendment and Restated 2005 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) | unit		27,030,000		27,030,000
Fungible units per share (in fungible units per share) | unit / shares		3.74		3.74
Shares that may be issued if equal to fungible units (shares) (less than) | shares		27,030,000		27,030,000
Fungible units | fungible_unit		7.4		7.4
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		$ 1,600,000	1,900,000	$ 3,200,000	3,900,000
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		0.73
Award expiration period (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		1
Award expiration period (in years)				10 years
2014 Outperformance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense		$ 0	4,300,000	$ 0	6,300,000
Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options				27,900,000
LTIP units earned (in shares) | shares	610,000
Award period (in years)	3 years
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, second performance period	0.667
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		$ 100,000	$ 200,000	$ 2,100,000	$ 2,100,000
Maximum percentage of the annual retainer fee, chairman fees and meeting fees that may be deferred by non-employee directors (percent)		100.00%		100.00%
Awards granted (in shares) | shares				11,502
Shares issued (in shares) | shares				9,332
Awards outstanding (in shares) | shares		111,356		111,356
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock available for issuance (shares) | shares								500,000
Duration of each offering period starting the first day of each calendar quarter (in months)				3 months
Discount from market price				85.00%
Shares of common stock issued (shares) | shares		110,045		110,045

Share-based Compensation - Stoc

Share-based Compensation - Stock Options and Restricted Stock Activity (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
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%
Expected life of option (in years)	3 years 6 months		4 years 4 months 24 days
Risk-free interest rate (as a percent)	2.48%		1.73%
Expected stock price volatility (as a percent)	22.00%		28.10%
Options Outstanding
Balance at beginning of period (in shares)	1,548,719	1,737,213	1,737,213
Granted (in shares)	6,000		174,000
Exercised (in shares)	(58,734)		(292,193)
Lapsed or cancelled (in shares)	(56,033)		(70,301)
Balance at end of period (in shares)	1,439,952		1,548,719
Options exercisable at end of period (in shares)	1,067,969		800,902
Total fair value of options granted during the period	$ 84,068		$ 3,816,652
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 101.48	$ 98.44	$ 98.44
Granted (in dollars per share)	97.91		105.66
Exercised (in dollars per share)	89.62		81.07
Lapsed or cancelled (in dollars per share)	114.70		121.68
Balance at end of period (in dollars per share)	101.43		101.48
Options exercisable at end of period (in dollars per share)	$ 98.93		$ 94.33
Restricted Stock Awards
Options Outstanding
Total fair value of options granted during the period	$ 163,831	$ 9,905,986
Summary of restricted stock
Balance at beginning of year (in shares)	3,298,216	3,202,031	3,202,031
Granted (in shares)	1,700	96,185
Cancelled (in shares)	(8,300)	0
Balance at end of period (in shares)	3,291,616		3,298,216
Vested during the period (in shares)	92,114	95,736

Accumulated Other Comprehensi85

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	$ 6,589,454
Other comprehensive (loss) income before reclassifications	13,920
Amounts reclassified from accumulated other comprehensive income	98
Ending Balance	6,242,056
Deferred net losses from terminated hedges	2,200	$ 3,200
Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	12,542
Other comprehensive (loss) income before reclassifications	9,837
Amounts reclassified from accumulated other comprehensive income	237
Ending Balance	22,616
Net unrealized gain on marketable securities
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	1,042
Other comprehensive (loss) income before reclassifications	(14)
Amounts reclassified from accumulated other comprehensive income	0
Ending Balance	1,028
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	18,604
Ending Balance	32,622
Joint venture | Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	5,020
Other comprehensive (loss) income before reclassifications	4,097
Amounts reclassified from accumulated other comprehensive income	(139)
Ending Balance	$ 8,978

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Fair Value of Financial Instruments
Marketable securities		$ 28,570,000		$ 28,570,000		$ 28,579,000
Interest rate cap and swap agreements (included in other assets)		26,132,000		26,132,000		16,692,000
Purchase price and other fair value adjustments		11,149,000	$ 0	60,442,000	$ 0
Debt and preferred equity investments		2,168,515,000		2,168,515,000		2,114,041,000
Equity method investments		3,059,985,000		3,059,985,000		2,362,989,000
Additional amount of financing receivables included in other assets		89,600,000		89,600,000		65,500,000
Carrying Value
Fair Value of Financial Instruments
Debt and preferred equity investments		2,168,515,000		2,168,515,000		2,114,041,000
Fixed rate debt		3,765,899,000		3,765,899,000		4,305,165,000
Variable rate debt		2,137,000,000		2,137,000,000		1,605,431,000
Total		5,902,899,000		5,902,899,000		5,910,596,000
Fair Value
Fair Value of Financial Instruments
Marketable securities		28,570,000		28,570,000		28,579,000
Total		5,948,223,000		5,948,223,000		6,034,090,000
Estimated fair value of debt and preferred equity investments, low end of range		2,200,000,000		2,200,000,000		2,100,000,000
Estimated fair value of debt and preferred equity investments, high end of range		2,400,000,000		2,400,000,000		2,300,000,000
Level 1
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in other assets)		0		0		0
Level 2
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in other assets)		26,132,000		26,132,000		16,692,000
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
Level 3 | Fair Value
Fair Value of Financial Instruments
Fixed rate debt		3,796,225,000		3,796,225,000		4,421,866,000
Variable rate debt		2,151,998,000		2,151,998,000		1,612,224,000
Equity marketable securities | Level 1
Fair Value of Financial Instruments
Marketable securities		0		0		0
Commercial mortgage-backed securities
Fair Value of Financial Instruments
Marketable securities		28,570,000		28,570,000		28,579,000
Commercial mortgage-backed securities | Level 2
Fair Value of Financial Instruments
Marketable securities		28,570,000		28,570,000		28,579,000
Mezzanine/Jr. Mortgage Loan with an Initial Maturity Date of April 2017
Fair Value of Financial Instruments
Debt and preferred equity investments		250,500,000		250,500,000		0	$ 0
Total fixed rate | Mezzanine/Jr. Mortgage Loan with an Initial Maturity Date of April 2017
Fair Value of Financial Instruments
Notes receivable		250,500,000		250,500,000
Accrued interest		7,700,000		7,700,000
Joint venture
Fair Value of Financial Instruments
Equity method investments		3,059,985,000		$ 3,059,985,000		$ 2,362,989,000
919 Third Avenue | Joint venture | 919 Third Avenue
Fair Value of Financial Instruments
Purchase price and other fair value adjustments		$ 49,300,000
2 Herald Square
Fair Value of Financial Instruments
Business combination, fair value adjustment	$ 11,100,000

Financial Instruments_ Deriva87

Financial Instruments: Derivatives and Hedging (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financial Instruments: Derivatives and Hedging
Fair Value	$ 26,132,000		$ 26,132,000
Gain (loss) from changes in fair value	100,000	$ 0	(300,000)	$ 100,000
Fair value of derivatives in a net liability position	0		0
Aggregate termination value	0		0
Estimated current balance held in accumulated other comprehensive loss to be reclassified into earnings within the next 12 months			2,600,000
Share of joint venture of accumulated other comprehensive loss reclassified into equity in net income from unconsolidated joint ventures within the next 12 months			1,400,000
Amount of Gain (Loss) Recognized in Other Comprehensive Loss (Effective Portion)	4,208,000	(3,364,000)	14,803,000	(6,160,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	231,000	(811,000)	(99,000)	(2,189,000)
Amount of Gain (Loss) Recognized into Income (Ineffective Portion)	(33,000)	34,000	(131,000)	(69,000)
Interest Rate Swap Expiring in July 2023
Financial Instruments: Derivatives and Hedging
Notional Value	$ 200,000,000		$ 200,000,000
Strike Rate	1.131%		1.131%
Fair Value	$ 15,272,000		$ 15,272,000
Interest Rate Swap Expiring in July 2023
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000,000		$ 100,000,000
Strike Rate	1.161%		1.161%
Fair Value	$ 7,496,000		$ 7,496,000
Interest Rate Cap Expiring September 2019
Financial Instruments: Derivatives and Hedging
Notional Value	$ 137,500,000		$ 137,500,000
Strike Rate	4.00%		4.00%
Fair Value	$ 1,000		$ 1,000
Interest Rate Swap Expiring November 2020
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000,000		$ 100,000,000
Strike Rate	1.928%		1.928%
Fair Value	$ 1,688,000		$ 1,688,000
Interest Rate Swap Expiring November 2020, 2
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000,000		$ 100,000,000
Strike Rate	1.934%		1.934%
Fair Value	$ 1,675,000		$ 1,675,000
Interest Rate Swaps/Caps
Financial Instruments: Derivatives and Hedging
Amount of Gain (Loss) Recognized in Other Comprehensive Loss (Effective Portion)	3,116,000	(2,036,000)	10,398,000	(5,173,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	76,000	(519,000)	(253,000)	(1,498,000)
Amount of Gain (Loss) Recognized into Income (Ineffective Portion)	(3,000)	0	(12,000)	(8,000)
Joint venture
Financial Instruments: Derivatives and Hedging
Amount of Gain (Loss) Recognized in Other Comprehensive Loss (Effective Portion)	1,092,000	(1,328,000)	4,405,000	(987,000)
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	155,000	(292,000)	154,000	(691,000)
Amount of Gain (Loss) Recognized into Income (Ineffective Portion)	$ (30,000)	$ 34,000	$ (119,000)	$ (61,000)

Commitments and Contingencies88

Commitments and Contingencies (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Initial term of non cancellable operating leases, minimum (in years)	1 year
Capital lease
Remaining 2,018	$ 5,324
2,019	10,826
2,020	11,245
2,021	11,635
2,022	11,856
2,023	12,083
Thereafter	1,391,127
Total minimum lease payments	1,454,096
Amount representing interest	(1,145,484)
Amount classified within liabilities held for sale	(265,391)
Capital lease obligations	43,221
Non-cancellable operating leases
Remaining 2,018	17,917
2,019	35,943
2,020	36,435
2,021	36,751
2,022	34,723
2,023	32,548
Thereafter	1,008,718
Total minimum lease payments	$ 1,203,035

Segment Information - Additiona

Segment Information - Additional Information (Details) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)segment	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Segment information
Number of reportable segments (segment) | segment				2
Total revenues		$ 301,116	$ 398,150	$ 602,811	$ 775,531
Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities		47,515	35,813	94,964	87,133
Total assets	[1]	13,713,928		13,713,928		$ 13,982,904
Marketing, general and administrative		22,479	24,256	46,007	48,399
Operating Segments | Real Estate Segment
Segment information
Total revenues		251,843	337,528	508,248	674,610
Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities		13,239	(16,232)	27,263	(2,425)
Total assets		11,249,972		11,249,972		11,631,700
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues		49,273	60,622	94,563	100,921
Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities		34,276	$ 52,045	67,701	$ 89,558
Total assets		$ 2,463,956		$ 2,463,956		$ 2,351,204
[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: $175.0 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, $32.2 million and $330.9 million of accumulated depreciation, $860.2 million and $221.0 million of other assets included in other line items, $136.2 million and $628.9 million of real estate debt, net, $0.4 million and $2.5 million of accrued interest payable, $43.2 million and $42.8 million of capital lease obligations, and $155.6 million and $56.8 million of other liabilities included in other line items as of June 30, 2018 and December 31, 2017, respectively.

Segment Information - Schedule

Segment Information - Schedule of Reconciliation of Income from Continuing Operations to Net Income Attributable to SL Green Common Stockholders (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reconciliation of income from continuing operations to net income attributable to SL Green common stockholders
Net income (loss) before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price and other fair value adjustments, (loss) gain on sale of real estate net, depreciable real estate reserves, and gain on sale of marketable securities	$ 47,515	$ 35,813	$ 94,964	$ 87,133
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	72,025	13,089	65,585	15,136
Purchase price and other fair value adjustments	11,149	0	60,442	0
(Loss) gain on sale of real estate, net	(14,790)	(3,823)	8,731	(3,256)
Depreciable real estate reserves	0	(29,064)	0	(85,336)
Gain on sale of investment in marketable securities	0	0	0	3,262
Net income	$ 115,899	$ 16,015	$ 229,722	$ 16,939