SL Green Realty (SLG) 10-K 28 Feb 20 2019 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Feb. 27, 2020	Jun. 30, 2019
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	1-13199
Entity Registrant Name	SL GREEN REALTY CORP
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	13-3956775
Entity Address, Address Line One	420 Lexington Avenue
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10170
City Area Code	212
Local Phone Number	594-2700
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		77,935,496
Entity Public Float			$ 6.1
Entity Central Index Key	0001040971
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the SL Green Realty Corp.'s Proxy Statement for its 2020 Annual Stockholders' Meeting to be filed within 120 days after the end of the Registrant's fiscal year are incorporated by reference into Part III of this Annual Report on Form 10-K.
Common Stock
Document Information [Line Items]
Trading Symbol	SLG
Title of 12(b) Security	Common Stock, $0.01 par value
Security Exchange Name	NYSE
Preferred Stock
Document Information [Line Items]
Trading Symbol	SLG.PRI
Title of 12(b) Security	6.500% Series I Cumulative Redeemable Preferred Stock, $0.01 par value
Security Exchange Name	NYSE
SL Green Operating Partnership
Document Information [Line Items]
Entity File Number	33-167793-02
Entity Registrant Name	SL GREEN OPERATING PARTNERSHIP, L.P.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-3960938
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,025,366
Entity Central Index Key	0001492869
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Commercial real estate properties, at cost:
Land and land interests		$ 1,751,544	$ 1,774,899
Building and improvements		5,154,990	5,268,484
Building leasehold and improvements		1,433,793	1,423,107
Right of use asset - financing leases		47,445	47,445
Right of use asset - operating leases		396,795	0
Total commercial real estate properties, at cost		8,784,567	8,513,935
Less: accumulated depreciation		(2,060,560)	(2,099,137)
Total commercial real estate properties, net		6,724,007	6,414,798
Assets held for sale		391,664	0
Cash and cash equivalents		166,070	129,475
Restricted cash		75,360	149,638
Investments in marketable securities		29,887	28,638
Tenant and other receivables, net of allowance of $12,369 and $15,702 in 2019 and 2018, respectively		43,968	41,589
Related party receivables		21,121	28,033
Deferred rents receivable, net of allowance of $12,477 and $15,457 in 2019 and 2018, respectively		283,011	335,985
Debt and preferred equity investments, net of discounts and deferred origination fees of $14,562 and $22,379 and allowances of $1,750 and $5,750 in 2019 and 2018, respectively		1,580,306	2,099,393
Investments in unconsolidated joint ventures		2,912,842	3,019,020
Deferred costs, net		205,283	209,110
Other assets		332,801	295,679
Total assets		12,766,320	12,751,358
Liabilities
Mortgages and other loans payable, net		2,183,253	1,961,240
Revolving credit facility, net		234,013	492,196
Unsecured term loans, net		1,494,024	1,493,051
Unsecured notes, net		1,496,847	1,495,214
Accrued interest payable		22,148	23,154
Other liabilities		177,080	116,566
Accounts payable and accrued expenses		166,905	147,060
Deferred revenue		114,052	94,453
Lease liability - financing leases		44,448	43,616
Lease liability - operating leases		381,671	3,603
Dividend and distributions payable		79,282	80,430
Security deposits		62,252	64,688
Liabilities related to assets held for sale		0	0
Junior subordinated deferrable interest debentures held by trusts that issued trust preferred securities		100,000	100,000
Total liabilities	[1]	6,555,975	6,115,271
Commitments and contingencies
Noncontrolling interests in Operating Partnership		409,862	387,805
Preferred units		283,285	300,427
Equity
Series I Preferred Stock, $0.01 par value, $25.00 liquidation preference, 9,200 issued and outstanding at both December 31, 2019 and 2018		221,932	221,932
Common stock, $0.01 par value, 160,000 shares authorized and 80,257 and 84,739 issued and outstanding at December 31, 2019 and 2018, respectively (including 1,055 and 1,055 shares held in treasury at December 31, 2019 and 2018, respectively)		803	847
Additional paid-in-capital		4,286,395	4,508,685
Treasury stock at cost		(124,049)	(124,049)
Accumulated other comprehensive (loss) income		(28,485)	15,108
Retained earnings		1,084,719	1,278,998
Total SL Green stockholders' equity		5,441,315	5,901,521
Noncontrolling interests in other partnerships		75,883	46,334
Total equity		5,517,198	5,947,855
SL Green stockholders equity:
Total liabilities and equity/capital		12,766,320	12,751,358
SL Green Operating Partnership
Commercial real estate properties, at cost:
Land and land interests		1,751,544	1,774,899
Building and improvements		5,154,990	5,268,484
Building leasehold and improvements		1,433,793	1,423,107
Right of use asset - financing leases		47,445	47,445
Right of use asset - operating leases		396,795	0
Total commercial real estate properties, at cost		8,784,567	8,513,935
Less: accumulated depreciation		(2,060,560)	(2,099,137)
Total commercial real estate properties, net		6,724,007	6,414,798
Assets held for sale		391,664	0
Cash and cash equivalents		166,070	129,475
Restricted cash		75,360	149,638
Investments in marketable securities		29,887	28,638
Tenant and other receivables, net of allowance of $12,369 and $15,702 in 2019 and 2018, respectively		43,968	41,589
Related party receivables		21,121	28,033
Deferred rents receivable, net of allowance of $12,477 and $15,457 in 2019 and 2018, respectively		283,011	335,985
Debt and preferred equity investments, net of discounts and deferred origination fees of $14,562 and $22,379 and allowances of $1,750 and $5,750 in 2019 and 2018, respectively		1,580,306	2,099,393
Investments in unconsolidated joint ventures			3,019,020
Deferred costs, net		205,283	209,110
Other assets		332,801	295,679
Total assets	[2]	12,766,320	12,751,358
Liabilities
Mortgages and other loans payable, net		2,183,253	1,961,240
Revolving credit facility, net		234,013	492,196
Unsecured term loans, net		1,494,024	1,493,051
Unsecured notes, net		1,496,847	1,495,214
Accrued interest payable		22,148	23,154
Other liabilities		177,080	116,566
Accounts payable and accrued expenses		166,905	147,060
Deferred revenue		114,052	94,453
Lease liability - financing leases		44,448	43,616
Lease liability - operating leases		381,671	3,603
Dividend and distributions payable		79,282	80,430
Security deposits		62,252	64,688
Liabilities related to assets held for sale		0	0
Junior subordinated deferrable interest debentures held by trusts that issued trust preferred securities		100,000	100,000
Total liabilities	[2]	6,555,975	6,115,271
Commitments and contingencies
Limited partner interests in SLGOP (4,196 and 4,131 limited partner common units outstanding at December 31, 2019 and 2018, respectively)		409,862	387,805
Preferred units		283,285	300,427
Equity
Accumulated other comprehensive (loss) income		(28,485)	15,108
SL Green stockholders equity:
Series I Preferred Units, $25.00 liquidation preference, 9,200 issued and outstanding at both December 31, 2019 and 2018		221,932	221,932
SL Green partners' capital (834 and 878 general partner common units, and 78,368 and 82,806 limited partner common units outstanding at December 31, 2019 and 2018, respectively)		5,247,868	5,664,481
Total SLGOP partners' capital		5,441,315	5,901,521
Noncontrolling interests in other partnerships		75,883	46,334
Total capital		5,517,198	5,947,855
Total liabilities and equity/capital		$ 12,766,320	$ 12,751,358
[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: $205.2 million and $110.0 million of land, $481.9 million and $346.7 million of building and improvements, $2.0 million and $2.0 million of building and leasehold improvements, $61.7 million and $47.4 million of right of use assets, $17.6 million and $42.2 million of accumulated depreciation, $169.5 million and $112.6 million of other assets included in other line items, $457.1 million and $140.8 million of real estate debt, net, $1.2 million and $0.4 million of accrued interest payable, $57.7 million and $43.6 million of lease liabilities, and $43.7 million and $18.3 million of other liabilities included in other line items as of December 31, 2019 and December 31, 2018, 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: $205.2 million and $110.0 million of land, $481.9 million and $346.7 million of building and improvements, $2.0 million and $2.0 million of building and leasehold improvements, $61.7 million and $47.4 million of right of use assets, $17.6 million and $42.2 million of accumulated depreciation, $169.5 million and $112.6 million of other assets included in other line items, $457.1 million and $140.8 million of real estate debt, net, $1.2 million and $0.4 million of accrued interest payable, $57.7 million and $43.6 million of lease liabilities, and $43.7 million and $18.3 million of other liabilities included in other line items as of December 31, 2019 and December 31, 2018, respectively.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Tenant and other receivables, allowance	$ 12,369	$ 15,702
Deferred rents receivable, allowance	12,477	15,457
Debt and preferred equity investments, net of discounts and deferred origination fees	14,562	22,379
Allowance for loan and lease losses	$ 1,750	$ 5,750
Preferred stock, par (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)	80,258,000	84,739,000
Common stock, shares outstanding (in shares)	80,258,000	84,739,000
Treasury stock, shares (in shares)	1,055,000	1,055,000
Land	$ 1,751,544	$ 1,774,899
Building and improvements	5,154,990	5,268,484
Building leasehold and improvements	1,433,793	1,423,107
Right of use asset - financing leases	47,445	47,445
Accumulated depreciation	2,060,560	2,099,137
Other assets	332,801	295,679
Real estate debt	2,183,253	1,961,240
Accrued interest payable	22,148	23,154
Lease liabilities	44,448	43,616
Other liabilities	177,080	116,566
SL Green Operating Partnership
Tenant and other receivables, allowance	12,369	15,702
Deferred rents receivable, allowance	12,477	15,457
Debt and preferred equity investments, net of discounts and deferred origination fees	14,562	22,379
Allowance for loan and lease losses	$ 1,750	$ 5,750
Limited partner interests in Operating Partnership, limited partner common units outstanding (shares)	4,196,000	4,131,000
SL Green partner's capital, general partner common units outstanding (shares)	834,000	878,000
SL Green partners' capital, limited partner common units outstanding (shares)	78,368,000	82,806,000
Land	$ 1,751,544	$ 1,774,899
Building and improvements	5,154,990	5,268,484
Building leasehold and improvements	1,433,793	1,423,107
Right of use asset - financing leases	47,445	47,445
Accumulated depreciation	2,060,560	2,099,137
Other assets	332,801	295,679
Real estate debt	2,183,253	1,961,240
Accrued interest payable	22,148	23,154
Lease liabilities	44,448	43,616
Other liabilities	177,080	116,566
Consolidated VIEs | SL Green Operating Partnership
Land	205,200	110,000
Building and improvements	481,900	346,700
Building leasehold and improvements	2,000	2,000
Right of use asset - financing leases	61,700	47,400
Accumulated depreciation	17,600	42,200
Other assets	169,500	112,600
Real estate debt	457,100	140,800
Accrued interest payable	1,200	400
Lease liabilities	57,700	43,600
Other liabilities	$ 43,700	$ 18,300
Series I Preferred Stock
Preferred stock, par (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 25	$ 25
Preferred stock, shares issued (in shares)	9,200,000	9,200,000
Preferred stock, shares outstanding (in shares)	9,200,000	9,200,000
Series I Preferred Stock | SL Green Operating Partnership
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

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues
Rental revenue, net	$ 983,557	$ 978,574	$ 1,273,932
Investment income	195,590	201,492	193,871
Other income	59,848	47,326	43,670
Total revenues	1,238,995	1,227,392	1,511,473
Expenses
Operating expenses, including $18,106 in 2019, $17,823 in 2018, $21,400 in 2017 of related party expenses	234,676	229,347	293,364
Real estate taxes	190,764	186,351	244,323
Operating lease rent	33,188	32,965	33,231
Interest expense, net of interest income	190,521	208,669	257,045
Amortization of deferred financing costs	11,653	12,408	16,498
Depreciation and amortization	272,358	279,507	403,320
Loan loss and other investment reserves, net of recoveries	0	6,839	0
Transaction related costs	729	1,099	(1,834)
Marketing, general and administrative	100,875	92,631	100,498
Total expenses	1,034,764	1,049,816	1,346,445
Equity in net (loss) income from unconsolidated joint ventures	(34,518)	7,311	21,892
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	76,181	303,967	16,166
Purchase price and other fair value adjustment	69,389	57,385	0
(Loss) gain on sale of real estate, net	(16,749)	(30,757)	73,241
Depreciable real estate reserves and impairment	(7,047)	(227,543)	(178,520)
Gain on sale of investment in marketable securities	0	0	3,262
Loss on early extinguishment of debt	0	(17,083)	0
Net income	291,487	270,856	101,069
Net (income) loss attributable to noncontrolling interests:
Noncontrolling interests in the Operating Partnership	(13,301)	(12,216)	(3,995)
Net loss attributable to noncontrolling interests in other partnerships	3,159	6	15,701
Preferred unit distributions	(10,911)	(11,384)	(11,401)
Net income (loss) attributable to SL Green/SLGOP	270,434	247,262	101,374
Perpetual preferred stock dividends	(14,950)	(14,950)	(14,950)
Net income attributable to SL Green common stockholders	$ 255,484	$ 232,312	$ 86,424
Basic weighted average common shares outstanding (in shares)	81,733	86,753	98,571
Diluted weighted average common shares and common share equivalents outstanding (in shares)	86,562	91,530	103,403
SL Green Operating Partnership
Revenues
Rental revenue, net	$ 983,557	$ 978,574	$ 1,273,932
Investment income	195,590	201,492	193,871
Other income	59,848	47,326	43,670
Total revenues	1,238,995	1,227,392	1,511,473
Expenses
Operating expenses, including $18,106 in 2019, $17,823 in 2018, $21,400 in 2017 of related party expenses	234,676	229,347	293,364
Real estate taxes	190,764	186,351	244,323
Operating lease rent	33,188	32,965	33,231
Interest expense, net of interest income	190,521	208,669	257,045
Amortization of deferred financing costs	11,653	12,408	16,498
Depreciation and amortization	272,358	279,507	403,320
Loan loss and other investment reserves, net of recoveries	0	6,839	0
Transaction related costs	729	1,099	(1,834)
Marketing, general and administrative	100,875	92,631	100,498
Total expenses	1,034,764	1,049,816	1,346,445
Equity in net (loss) income from unconsolidated joint ventures	(34,518)	7,311	21,892
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	76,181	303,967	16,166
Purchase price and other fair value adjustment	69,389	57,385	0
(Loss) gain on sale of real estate, net	(16,749)	(30,757)	73,241
Depreciable real estate reserves and impairment	(7,047)	(227,543)	(178,520)
Gain on sale of investment in marketable securities	0	0	3,262
Loss on early extinguishment of debt	0	(17,083)	0
Net income	291,487	270,856	101,069
Net (income) loss attributable to noncontrolling interests:
Net loss attributable to noncontrolling interests in other partnerships	3,159	6	15,701
Preferred unit distributions	(10,911)	(11,384)	(11,401)
Net income (loss) attributable to SL Green/SLGOP	283,735	259,478	105,369
Perpetual preferred stock dividends	(14,950)	(14,950)	(14,950)
Net income attributable to SLGOP common unitholders	$ 268,785	$ 244,528	$ 90,419
Basic earnings per unit (in dollars per share)	$ 3.10	$ 2.67	$ 0.87
Diluted earnings per unit (in dollars per share)	$ 3.10	$ 2.67	$ 0.87
Basic weighted average common shares outstanding (in shares)	86,008	91,315	103,127
Basic weighted average common units outstanding (in shares)	86,008	91,315	103,127
Diluted weighted average common shares and common share equivalents outstanding (in shares)	86,562	91,530	103,403
Diluted weighted average common units and common unit equivalents outstanding (in shares)	86,562	91,530	103,403

Consolidated Statements of Op_2

Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses, paid to related parties	$ 18,106	$ 17,823	$ 21,400
SL Green Operating Partnership
Operating expenses, paid to related parties	$ 18,106	$ 17,823	$ 21,400

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income	$ 291,487	$ 270,856	$ 101,069
Other comprehensive (loss) income:
(Decrease) increase in unrealized value of derivative instruments, including SLGOP's share of joint venture derivative instruments	(47,118)	(3,622)	1,040
Increase (decrease) in unrealized value of marketable securities	1,249	60	(4,667)
Other comprehensive loss	(45,869)	(3,562)	(3,627)
Comprehensive income	245,618	267,294	97,442
Net (income) loss attributable to noncontrolling interests and preferred units distributions	(21,053)	(23,594)	305
Net loss attributable to noncontrolling interests	3,159	6	15,701
Other comprehensive loss attributable to noncontrolling interests	2,276	66	94
Comprehensive income attributable to SL Green/SLGOP	226,841	243,766	97,841
SL Green Operating Partnership
Net income	291,487	270,856	101,069
Other comprehensive (loss) income:
(Decrease) increase in unrealized value of derivative instruments, including SLGOP's share of joint venture derivative instruments	(47,118)	(3,622)	1,040
Increase (decrease) in unrealized value of marketable securities	1,249	60	(4,667)
Other comprehensive loss	(45,869)	(3,562)	(3,627)
Comprehensive income	245,618	267,294	97,442
Net loss attributable to noncontrolling interests	3,159	6	15,701
Other comprehensive loss attributable to noncontrolling interests	2,276	66	94
Comprehensive income attributable to SL Green/SLGOP	$ 251,053	$ 267,366	$ 113,237

Consolidated Statement of Equit

Consolidated Statement of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid- In-Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Noncontrolling Interests	Series I Preferred StockPreferred Stock
Beginning Balance at Dec. 31, 2016	$ 7,750,911	$ 1,017	$ 5,624,545	$ (124,049)	$ 22,137	$ 1,578,893	$ 426,436	$ 221,932
Beginning Balance (in shares) at Dec. 31, 2016		100,562
Increase (Decrease) in Stockholders' Equity
Net income (loss)	85,673					101,374	(15,701)
Other comprehensive loss	(3,533)				(3,533)
Preferred dividends	(14,950)					(14,950)
DRSPP (in shares)		2
DRSPP proceeds	223		223
Conversion of units of the Operating Partnership to common stock (in shares)		202
Conversion of units in the Operating Partnership to common stock	21,574	$ 2	21,572
Reallocation of noncontrolling interest in the Operating Partnership	5,712					5,712
Equity component of repurchased exchangeable senior notes	(109,776)		(109,776)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)		87
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	29,787	$ 1	29,786
Repurchases of common stock (in shares)		(8,342)
Repurchases of common units	(848,048)	$ (83)	(621,324)			(226,641)
Proceeds from stock options exercised (in shares)		292
Proceeds from stock options exercised	23,314	$ 2	23,312
Contributions to consolidated joint venture interests	36,275						36,275
Deconsolidation of partially owned entity	(30,203)						(30,203)
Cash distributions to noncontrolling interests	(52,446)						(52,446)
Cash distributions declared ( per common share, none of which represented a return of capital for federal income tax purposes)	(305,059)					(305,059)
Deconsolidation of partially owned entity	(30,203)						(30,203)
Ending Balance at Dec. 31, 2017	6,589,454	$ 939	4,968,338	(124,049)	18,604	1,139,329	364,361	221,932
Ending Balance (in shares) at Dec. 31, 2017		92,803
Increase (Decrease) in Stockholders' Equity
Adjusted Balance	7,159,978	$ 939	4,968,338	(124,049)	18,604	1,709,853	364,361	221,932
Net income (loss)	247,256					247,262	(6)
Other comprehensive loss	(3,496)				(3,496)
Preferred dividends	(14,950)					(14,950)
DRSPP (in shares)		1
DRSPP proceeds	136		136
Conversion of units of the Operating Partnership to common stock (in shares)		160
Conversion of units in the Operating Partnership to common stock	16,303	$ 2	16,301
Reallocation of noncontrolling interest in the Operating Partnership	34,236					34,236
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)		149
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	17,484	$ 1	17,483
Repurchases of common stock (in shares)		(9,745)
Repurchases of common units	(937,795)	$ (98)	(522,482)			(415,215)
Proceeds from stock options exercised (in shares)		316
Proceeds from stock options exercised	28,912	$ 3	28,909
Contributions to consolidated joint venture interests	5,459						5,459
Deconsolidation of partially owned entity	(315,116)						(315,116)
Cash distributions to noncontrolling interests	(8,364)						(8,364)
Cash distributions declared ( per common share, none of which represented a return of capital for federal income tax purposes)	(282,188)					(282,188)
Deconsolidation of partially owned entity	(315,116)						(315,116)
Ending Balance at Dec. 31, 2018	5,947,855	$ 847	4,508,685	(124,049)	15,108	1,278,998	46,334	221,932
Ending Balance (in shares) at Dec. 31, 2018		83,684
Increase (Decrease) in Stockholders' Equity
Net income (loss)	267,275					270,434	(3,159)
Other comprehensive loss	(43,593)				(43,593)
Preferred dividends	(14,950)					(14,950)
DRSPP (in shares)		4
DRSPP proceeds	334		334
Conversion of units of the Operating Partnership to common stock (in shares)		5
Conversion of units in the Operating Partnership to common stock	471		471
Reallocation of noncontrolling interest in the Operating Partnership	(34,320)					(34,320)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)		105
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	25,763	$ 2	25,761
Repurchases of common stock (in shares)		(4,596)
Repurchases of common units	(384,399)	$ (46)	(248,287)			(136,066)
Contributions to consolidated joint venture interests	58,462						58,462
Cash distributions to noncontrolling interests	(478)						(478)
Cash distributions declared ( per common share, none of which represented a return of capital for federal income tax purposes)	(279,377)					(279,377)
Redemption of common units	(25,845)		(569)				(25,276)
Ending Balance at Dec. 31, 2019	$ 5,517,198	$ 803	$ 4,286,395	$ (124,049)	$ (28,485)	$ 1,084,719	$ 75,883	$ 221,932
Ending Balance (in shares) at Dec. 31, 2019		79,202

Consolidated Statement of Equ_2

Consolidated Statement of Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Stockholders' Equity [Abstract]
Cash distribution declared, per common share (in dollars per share)	$ 3.435	$ 3.2875	$ 3.1375

Consolidated Statement of Capit

Consolidated Statement of Capital - USD ($) shares in Thousands, $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Increase (Decrease) in Partner's Capital
Preferred dividends	$ (3,086)	$ (5,239)	$ 838	$ (8,319)
DRSPP proceeds					$ 334	$ 136	$ 223
Reallocation of noncontrolling interests in the operating partnership					(34,320)	34,236	5,712
Equity component of repurchased exchangeable senior notes							(109,776)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings					25,763	17,484	29,787
Repurchases of common units					(384,399)	(937,795)	(848,048)
Deconsolidation of partially owned entity						(315,116)	(30,203)
Cash distributions to noncontrolling interests					(478)	(8,364)	(52,446)
Conversion of common units					471	16,303	21,574
Redemption of common units					$ (25,845)
Proceeds from stock options exercised						$ 28,912	$ 23,314
Common Stock
Increase (Decrease) in Partner's Capital
DRSPP proceeds (in units)					4	1	2
DRSPP proceeds
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in units)					105	149	87
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings					$ 2	$ 1	$ 1
Repurchases of common units (in units)					(4,596)	(9,745)	(8,342)
Repurchases of common units					$ (46)	$ (98)	$ (83)
Conversion of common units						$ 2	$ 2
Proceeds from stock options exercised (in shares)						316	292
Proceeds from stock options exercised						$ 3	$ 2
Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Deconsolidation of partially owned entity						(315,116)	(30,203)
Cash distributions to noncontrolling interests					(478)	(8,364)	(52,446)
Redemption of common units					(25,276)
SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Beginning Balance		5,947,855		6,589,454	5,947,855	6,589,454	7,750,911
Adjusted Balance							7,159,978
Net income					267,275	247,256	85,673
Other comprehensive income (loss)					(43,593)	(3,496)	(3,533)
Preferred dividends	(2,091)	(2,961)	(2,601)	(3,047)	(14,950)	(14,950)	(14,950)
DRSPP proceeds					334	136	223
Reallocation of noncontrolling interests in the operating partnership					(34,320)	34,236	5,712
Equity component of repurchased exchangeable senior notes							(109,776)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings					25,763	17,484	29,787
Repurchases of common units					(384,399)	(937,795)
Proceeds from stock options exercised							23,314
Contributions to consolidated joint venture interests					58,462	5,459	36,275
Deconsolidation of partially owned entity						(315,116)
Cash distributions to noncontrolling interests					(478)	(8,364)	(52,446)
Cash distributions declared (none of which represented a return of capital for federal income tax purposes)					(279,377)	(282,188)	(305,059)
Conversion of common units					471	16,303	21,574
Redemption of common units					(25,845)
Proceeds from stock options exercised						28,912
Ending Balance	5,517,198		5,947,855		5,517,198	5,947,855	6,589,454
SL Green Operating Partnership | Preferred Units | Series I Preferred Stock
Increase (Decrease) in Partner's Capital
Beginning Balance		221,932		221,932	221,932	221,932	221,932
Adjusted Balance							221,932
Ending Balance	221,932		221,932		221,932	221,932	221,932
SL Green Operating Partnership | Common Stock | Partners' Interest
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 5,664,481		$ 5,984,557	$ 5,664,481	$ 5,984,557	$ 7,080,406
Beginning Balance (units)		83,684		92,803	83,684	92,803	100,562
Adjusted Balance							$ 6,555,081
Net income					$ 270,434	$ 247,262	101,374
Preferred dividends					$ (14,950)	$ (14,950)	$ (14,950)
DRSPP proceeds (in units)					4	1	2
DRSPP proceeds					$ 334	$ 136	$ 223
Reallocation of noncontrolling interests in the operating partnership					$ (34,320)	$ 34,236	5,712
Equity component of repurchased exchangeable senior notes							$ (109,776)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in units)					105	149	87
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings					$ 25,763	$ 17,484	$ 29,787
Repurchases of common units (in units)					(4,596)	(9,745)	(8,342)
Repurchases of common units					$ (384,399)	$ (937,795)	$ (848,048)
Proceeds from stock options exercised (in units)							292
Proceeds from stock options exercised							$ 23,314
Cash distributions declared (none of which represented a return of capital for federal income tax purposes)					$ (279,377)	$ (282,188)	$ (305,059)
Conversion of common units (in units)					5	160	202
Conversion of common units					$ 471	$ 16,303	$ 21,574
Redemption of common units					(569)
Proceeds from stock options exercised (in shares)						316
Proceeds from stock options exercised						$ 28,912
Ending Balance	$ 5,247,868		$ 5,664,481		$ 5,247,868	$ 5,664,481	$ 5,984,557
Ending Balance (units)	79,202		83,684		79,202	83,684	92,803
SL Green Operating Partnership | Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 15,108		$ 18,604	$ 15,108	$ 18,604	$ 22,137
Adjusted Balance							18,604
Other comprehensive income (loss)					(43,593)	(3,496)	(3,533)
Ending Balance	$ (28,485)		$ 15,108		(28,485)	15,108	18,604
SL Green Operating Partnership | Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Beginning Balance		$ 46,334		$ 364,361	46,334	364,361	426,436
Adjusted Balance							364,361
Net income					(3,159)	(6)	(15,701)
Contributions to consolidated joint venture interests					58,462	5,459	36,275
Deconsolidation of partially owned entity						(315,116)	(30,203)
Cash distributions to noncontrolling interests					(478)	(8,364)	(52,446)
Redemption of common units					(25,276)
Ending Balance	$ 75,883		$ 46,334		$ 75,883	$ 46,334	$ 364,361
Accounting Standards Update 2014-09
Increase (Decrease) in Partner's Capital
Cumulative adjustment upon adoption of ASC 610-20								$ 570,524
Accounting Standards Update 2014-09 | SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Cumulative adjustment upon adoption of ASC 610-20								570,524
Accounting Standards Update 2014-09 | SL Green Operating Partnership | Common Stock | Partners' Interest
Increase (Decrease) in Partner's Capital
Cumulative adjustment upon adoption of ASC 610-20								$ 570,524

Consolidated Statement of Cap_2

Consolidated Statement of Capital (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash distribution declared, per common share (in dollars per share)	$ 3.435	$ 3.2875	$ 3.1375
SL Green Operating Partnership
Cash distribution declared, per common share (in dollars per share)	$ 3.435	$ 3.2875	$ 3.1375

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities
Net income		$ 291,487	$ 270,856	$ 101,069
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		284,011	289,899	418,798
Equity in net loss (income) from unconsolidated joint ventures		34,518	(7,311)	(21,892)
Distributions of cumulative earnings from unconsolidated joint ventures		864	10,277	20,309
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate		(76,181)	(303,967)	(16,166)
Purchase price and other fair value adjustments		(69,389)	(57,385)	0
Depreciable real estate reserves and impairment		7,047	227,543	178,520
Loss (gain) on sale of real estate, net		16,749	30,757	(73,241)
Loan loss reserves and other investment reserves, net of recoveries		0	6,839	0
Gain on sale of investments in marketable securities		0	0	(3,262)
Loss on early extinguishment of debt		0	17,083	0
Deferred rents receivable		(13,941)	(18,216)	(38,009)
Non-cash lease expense		13,744	2,016	1,020
Other non-cash adjustments		271	2,932	19,621
Changes in operating assets and liabilities:
Tenant and other receivables		(4,968)	6,968	(5,717)
Related party receivables		7,802	(1,044)	(7,209)
Deferred lease costs		(70,938)	(44,158)	(41,939)
Other assets		(18,630)	(8,310)	(23,068)
Accounts payable, accrued expenses, other liabilities and security deposits		(25,597)	4,410	(12,440)
Deferred revenue		10,824	12,348	46,607
Change in lease liability - operating leases		(11,200)	0	0
Net cash provided by operating activities		376,473	441,537	543,001
Investing Activities
Acquisitions of real estate property		(262,591)	(60,486)	(28,680)
Additions to land, buildings and improvements		(252,986)	(254,460)	(336,001)
Acquisition deposits and deferred purchase price		(5,239)	0	0
Investments in unconsolidated joint ventures		(128,682)	(400,429)	(389,249)
Distributions in excess of cumulative earnings from unconsolidated joint ventures		79,020	233,118	319,745
Net proceeds from disposition of real estate/joint venture interest		208,302	1,231,004	692,796
Proceeds from sale of marketable securities		0	0	55,129
Other investments		(7,869)	(38,912)	25,330
Origination of debt and preferred equity investments		(607,844)	(731,216)	(1,129,970)
Repayments or redemption of debt and preferred equity investments		1,092,383	703,043	812,914
Net cash provided by investing activities		114,494	681,662	22,014
Financing Activities
Proceeds from mortgages and other loans payable		752,984	564,391	870,459
Repayments of mortgages and other loans payable		(230,076)	(868,842)	(902,460)
Proceeds from revolving credit facility and senior unsecured notes		1,310,000	3,120,000	2,784,599
Repayments of revolving credit facility and senior unsecured notes		(1,570,000)	(2,560,000)	(2,276,782)
Payment of debt extinguishment costs		0	(13,918)	0
Proceeds from stock options exercised and DRSPP issuance		334	29,048	23,537
Repurchase of common stock		(384,399)	(979,541)	(806,302)
Redemption of preferred stock		(18,142)	(1,208)	(275)
Redemption of OP units		(27,495)	(33,972)	0
Distributions to noncontrolling interests in other partnerships		(478)	(8,364)	(52,446)
Contributions from noncontrolling interests in other partnerships		10,239	5,459	36,275
Acquisition of subsidiary interest from noncontrolling interest		(25,845)	0	0
Distributions to noncontrolling interests in the Operating Partnership		(14,729)	(15,000)	(14,266)
Dividends/Distributions paid on common and preferred stock/units		(306,386)	(313,230)	(333,543)
Other obligations related to loan participations		0	16	17,227
Tax withholdings related to restricted share awards		(3,495)	(3,842)	(3,879)
Deferred loan costs		(21,162)	(15,109)	(27,100)
Net cash used in financing activities		(528,650)	(1,094,112)	(684,956)
Net (decrease) increase in cash, cash equivalents, and restricted cash		(37,683)	29,087	(119,941)
Cash, cash equivalents, and restricted cash at beginning of year		279,113	250,026	369,967
Cash, cash equivalents, and restricted cash at end of period		241,430	279,113	250,026
Supplemental Cash Flow Information [Abstract]
Interest paid		248,684	259,776	273,819
Income taxes paid		1,489	1,418	2,448
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the operating partnership		0	0	25,723
Conversion of units in the operating partnership		471	16,303	21,574
Redemption of units in the operating partnership for a joint venture sale		0	10,445	0
Exchange of debt investment for real estate or equity in joint venture		34,498	298,956	0
Tenant improvements and capital expenditures payable		6,056	0	6,667
Fair value adjustment to noncontrolling interest in the operating partnership		34,320	34,236	5,712
Deconsolidation of a subsidiary	[1]	395	298,404	695,204
Transfer of assets to assets held for sale		391,664	0	611,809
Transfer of liabilities related to assets held for sale		0	0	5,364
Removal of fully depreciated commercial real estate properties		19,577	124,249	15,488
Contribution to consolidated joint venture by noncontrolling interest		48,223	0	0
Share repurchase payable		0	0	41,746
Recognition of right of use assets and related lease liabilities		389,120	0	0
Total cash, cash equivalents, and restricted cash		279,113	279,113	369,967
SL Green Operating Partnership
Operating Activities
Net income		291,487	270,856	101,069
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		284,011	289,899	418,798
Equity in net loss (income) from unconsolidated joint ventures		34,518	(7,311)	(21,892)
Distributions of cumulative earnings from unconsolidated joint ventures		864	10,277	20,309
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate		(76,181)	(303,967)	(16,166)
Purchase price and other fair value adjustments		(69,389)	(57,385)	0
Depreciable real estate reserves and impairment		7,047	227,543	178,520
Loss (gain) on sale of real estate, net		16,749	30,757	(73,241)
Loan loss reserves and other investment reserves, net of recoveries		0	6,839	0
Gain on sale of investments in marketable securities		0	0	(3,262)
Loss on early extinguishment of debt		0	17,083	0
Deferred rents receivable		(13,941)	(18,216)	(38,009)
Non-cash lease expense		13,744	2,016	1,020
Other non-cash adjustments		271	2,932	19,621
Changes in operating assets and liabilities:
Tenant and other receivables		(4,968)	6,968	(5,717)
Related party receivables		7,802	(1,044)	(7,209)
Deferred lease costs		(70,938)	(44,158)	(41,939)
Other assets		(18,630)	(8,310)	(23,068)
Accounts payable, accrued expenses, other liabilities and security deposits		(25,597)	4,410	(12,440)
Deferred revenue		10,824	12,348	46,607
Change in lease liability - operating leases		(11,200)	0	0
Net cash provided by operating activities		376,473	441,537	543,001
Investing Activities
Acquisitions of real estate property		(262,591)	(60,486)	(28,680)
Additions to land, buildings and improvements		(252,986)	(254,460)	(336,001)
Acquisition deposits and deferred purchase price		(5,239)	0	0
Investments in unconsolidated joint ventures		(128,682)	(400,429)	(389,249)
Distributions in excess of cumulative earnings from unconsolidated joint ventures		79,020	233,118	319,745
Net proceeds from disposition of real estate/joint venture interest		208,302	1,231,004	692,796
Proceeds from sale of marketable securities		0	0	55,129
Other investments		(7,869)	(38,912)	25,330
Origination of debt and preferred equity investments		(607,844)	(731,216)	(1,129,970)
Repayments or redemption of debt and preferred equity investments		1,092,383	703,043	812,914
Net cash provided by investing activities		114,494	681,662	22,014
Financing Activities
Proceeds from mortgages and other loans payable		752,984	564,391	870,459
Repayments of mortgages and other loans payable		(230,076)	(868,842)	(902,460)
Proceeds from revolving credit facility and senior unsecured notes		1,310,000	3,120,000	2,784,599
Repayments of revolving credit facility and senior unsecured notes		(1,570,000)	(2,560,000)	(2,276,782)
Payment of debt extinguishment costs		0	(13,918)	0
Proceeds from stock options exercised and DRSPP issuance		334	29,048	23,537
Repurchase of common stock		(384,399)	(979,541)	(806,302)
Redemption of preferred stock		(18,142)	(1,208)	(275)
Redemption of OP units		(27,495)	(33,972)	0
Distributions to noncontrolling interests in other partnerships		(478)	(8,364)	(52,446)
Contributions from noncontrolling interests in other partnerships		10,239	5,459	36,275
Acquisition of subsidiary interest from noncontrolling interest		(25,845)	0	0
Dividends/Distributions paid on common and preferred stock/units		(321,115)	(328,230)	(347,809)
Other obligations related to loan participations		0	16	17,227
Tax withholdings related to restricted share awards		(3,495)	(3,842)	(3,879)
Deferred loan costs		(21,162)	(15,109)	(27,100)
Net cash used in financing activities		(528,650)	(1,094,112)	(684,956)
Net (decrease) increase in cash, cash equivalents, and restricted cash		(37,683)	29,087	(119,941)
Cash, cash equivalents, and restricted cash at beginning of year		279,113	250,026	369,967
Cash, cash equivalents, and restricted cash at end of period		241,430	279,113	250,026
Supplemental Cash Flow Information [Abstract]
Interest paid		248,684	259,776	273,819
Income taxes paid		1,489	1,418	2,448
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the operating partnership		0	0	25,723
Conversion of units in the operating partnership		471	16,303	21,574
Redemption of units in the operating partnership for a joint venture sale		0	10,445	0
Exchange of debt investment for real estate or equity in joint venture		34,498	298,956	0
Tenant improvements and capital expenditures payable		6,056	0	6,667
Fair value adjustment to noncontrolling interest in the operating partnership		34,320	34,236	5,712
Deconsolidation of a subsidiary	[2]	395	298,404	695,204
Transfer of assets to assets held for sale		391,664	0	611,809
Transfer of liabilities related to assets held for sale		0	0	5,364
Removal of fully depreciated commercial real estate properties		19,577	124,249	15,488
Contribution to consolidated joint venture by noncontrolling interest		48,223	0	0
Share repurchase payable		0	0	41,746
Recognition of right of use assets and related lease liabilities		389,120	0	0
Total cash, cash equivalents, and restricted cash		241,430	250,026	250,026
Preferred Units
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of preferred units relating to the real estate acquisition		1,000	0	0
Preferred Units | SL Green Operating Partnership
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of preferred units relating to the real estate acquisition		$ 1,000	$ 0	$ 0
[1]	$366.6 million of the 2017 amount relates to 1515 Broadway. In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. See Note 6, "Investments in Unconsolidated Joint Ventures.".
[2]	$366.6 million of the 2017 amount relates to 1515 Broadway. In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018.

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands		1 Months Ended		12 Months Ended
		Feb. 22, 2018	Nov. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly distributions declared, per share/unit (usd per share/unit)				$ 0.885	$ 0.85	$ 0.8125
Deconsolidation of a subsidiary	[1]			$ 395	$ 298,404	$ 695,204
SL Green Operating Partnership
Quarterly distributions declared, per share/unit (usd per share/unit)				$ 0.85	$ 0.8125	$ 0.775
Deconsolidation of a subsidiary	[2]			$ 395	$ 298,404	$ 695,204
Allianz Real Estate | 1515 Broadway
Deconsolidation of a subsidiary			$ 366,600
Ownership percentage in disposed asset		12.87%	30.13%
Allianz Real Estate | 1515 Broadway | SL Green Operating Partnership
Deconsolidation of a subsidiary			$ 366,600
Ownership percentage in disposed asset		12.87%	30.13%
[1]	$366.6 million of the 2017 amount relates to 1515 Broadway. In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. See Note 6, "Investments in Unconsolidated Joint Ventures.".
[2]	$366.6 million of the 2017 amount relates to 1515 Broadway. In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018.

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	Organization and Basis of Presentation SL Green Realty Corp., which is referred to as the Company or SL Green, a Maryland corporation, and SL Green Operating Partnership, L.P., which is referred to as SLGOP or the Operating Partnership, a Delaware limited partnership, were formed in June 1997 for the purpose of combining the commercial real estate business of S.L. Green Properties, Inc. and its affiliated partnerships and entities. The Operating Partnership received a contribution of interest in the real estate properties, as well as 95% of the economic interest in the management, leasing and construction companies which are referred to as the Service Corporation. All of the management, leasing and construction services that are provided to the properties that are wholly-owned by us and that are provided to certain joint ventures are conducted through SL Green Management LLC which is 100% owned by the Operating Partnership. The Company has qualified, and expects to qualify in the current fiscal year, as a real estate investment trust, or REIT, under the Internal Revenue Code of 1986, as amended, or the Code, and operates as a self-administered, self-managed REIT. A REIT is a legal entity that holds real estate interests and, through payments of dividends to stockholders, is permitted to minimize the payment of Federal income taxes at the corporate level. Unless the context requires otherwise, all references to "we," "our" and "us" means the Company and all entities owned or controlled by the Company, including the Operating Partnership. Substantially all of our assets are held by, and all of our operations are conducted through, the Operating Partnership. The Company is the sole managing general partner of the Operating Partnership. As of December 31, 2019 , noncontrolling investors held, in the aggregate, a 5.03% 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." As of December 31, 2019 , we owned the following interests in properties in the New York metropolitan area, primarily in midtown Manhattan. Our investments located outside of Manhattan are referred to as the Suburban properties: Consolidated Unconsolidated Total Location Property Type Number of Properties Approximate Square Feet (unaudited) Number of Properties Approximate Square Feet (unaudited) Number of Properties Approximate Square Feet (unaudited) Weighted Average Occupancy (1) (unaudited) Commercial: Manhattan Office 20 12,387,091 10 11,216,183 30 23,603,274 94.5 % Retail 6 (2) 320,430 8 289,050 14 609,480 98.4 % Development/Redevelopment (3) 6 189,538 1 — 7 189,538 84.9 % Fee Interest — — 1 — 1 — — % 32 12,897,059 20 11,505,233 52 24,402,292 94.6 % Suburban Office 8 1,044,800 — — 8 1,044,800 85.7 % Retail 1 52,000 — — 1 52,000 100.0 % 9 1,096,800 — — 9 1,096,800 86.4 % Total commercial properties 41 13,993,859 20 11,505,233 61 25,499,092 94.2 % Residential: Manhattan Residential 2 (2) 445,105 8 1,663,774 10 2,108,879 95.7 % Total residential properties 2 445,105 8 1,663,774 10 2,108,879 95.7 % Total portfolio 43 14,438,964 28 13,169,007 71 27,607,971 94.3 % (1) The weighted average occupancy for commercial properties represents the total occupied square footage divided by the total square footage at acquisition. The weighted average occupancy for residential properties represents the total occupied units divided by the total available units. (2) As of December 31, 2019 , 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. (3) Properties in Development are included in Number of Properties with no Approximate Square Feet. As of December 31, 2019 , we also managed two office buildings owned by third parties encompassing approximately 2.1 million square feet (unaudited) and held debt and preferred equity investments with a book value of $1.7 billion , including $0.1 billion of debt and preferred equity investments and other financing receivables that are included in balance sheet line items other than the Debt and Preferred Equity Investments line item. Partnership Agreement In accordance with the partnership agreement of the Operating Partnership, or the Operating Partnership Agreement, we allocate all distributions and profits and losses in proportion to the percentage of ownership interests of the respective partners, subject to the priority distributions with respect to preferred units and special provisions that apply to LTIP Units. 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. Subsequent Event In February 2020, The Company entered into contract to sell 315 West 33rd Street and an adjacent undeveloped parcel of land for a gross asset valuation of $446.5 million . This transaction is expected to close in the second quarter of 2020. At December 31, 2019 , we determined that the held for sale criteria was not met for this property as it was not probable that the sale of the asset would be completed within one year.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies Principles of Consolidation The consolidated financial statements include our accounts and those of our subsidiaries, which are wholly-owned or controlled by us. Entities which we do not control through our voting interest and entities which are variable interest entities, but where we are not the primary beneficiary, are accounted for under the equity method. See Note 5, "Debt and Preferred Equity Investments" and Note 6, "Investments in Unconsolidated Joint Ventures." All significant intercompany balances and transactions have been eliminated. We consolidate a VIE in which we are considered the primary beneficiary. The primary beneficiary is the entity that has (i) the power to direct the activities that most significantly impact the entity's economic performance and (ii) the obligation to absorb losses of the VIE or the right to receive benefits from the VIE that could be significant to the VIE. A noncontrolling interest in a consolidated subsidiary is defined as the portion of the equity (net assets) in a subsidiary not attributable, directly or indirectly, to us. Noncontrolling interests are required to be presented as a separate component of equity in the consolidated balance sheet and the presentation of net income is modified to present earnings and other comprehensive income attributed to controlling and noncontrolling interests. We assess the accounting treatment for each joint venture and debt and preferred equity investment. This assessment includes a review of each joint venture or limited liability company agreement to determine the rights provided to each party and whether those rights are protective or participating. For all VIEs, we review such agreements in order to determine which party has the power to direct the activities that most significantly impact the entity's economic performance. In situations where we and our partner approve, among other things, the annual budget, receive a detailed monthly reporting package, meet on a quarterly basis to review the results of the joint venture, review and approve the joint venture's tax return before filing, and approve all leases that cover more than a nominal amount of space relative to the total rentable space at each property, we do not consolidate the joint venture as we consider these to be substantive participation rights that result in shared power of the activities that most significantly impact the performance of the joint venture. Our joint venture agreements typically contain certain protective rights such as requiring partner approval to sell, finance or refinance the property and the payment of capital expenditures and operating expenditures outside of the approved budget or operating plan. Investment in Commercial Real Estate Properties Real estate properties are presented at cost less accumulated depreciation and amortization. Costs directly related to the development or redevelopment of properties are capitalized. Ordinary repairs and maintenance are expensed as incurred; major replacements and betterments, which improve or extend the life of the asset, are capitalized and depreciated over their estimated useful lives. We recognize the assets acquired, liabilities assumed (including contingencies) and any noncontrolling interests in an acquired entity at their respective fair values on the acquisition date. When we acquire our partner's equity interest in an existing unconsolidated joint venture and gain control over the investment, we record the consolidated investment at fair value. The difference between the book value of our equity investment on the purchase date and our share of the fair value of the investment's purchase price is recorded as a purchase price fair value adjustment in our consolidated statements of operations. See Note 3, "Property Acquisitions." We allocate the purchase price of real estate to land and building (inclusive of tenant improvements) and, if determined to be material, intangibles, such as the value of above- and below-market leases and origination costs associated with the in-place leases. We depreciate the amount allocated to building (inclusive of tenant improvements) over their estimated useful lives, which generally range from three to 40 years. We amortize the amount allocated to the above- and below-market leases over the remaining term of the associated lease, which generally range from one to 14 years, and record it as either an increase (in the case of below-market leases) or a decrease (in the case of above-market leases) to rental income. We amortize the amount allocated to the values associated with in-place leases over the expected term of the associated lease, which generally ranges from one to 14 years. If a tenant vacates its space prior to the contractual termination of the lease and no rental payments are being made on the lease, any unamortized balance of the related intangible will be written off. The tenant improvements and origination costs are amortized as an expense over the remaining life of the lease (or charged against earnings if the lease is terminated prior to its contractual expiration date). We assess fair value of the leases based on estimated cash flow projections that utilize appropriate discount and available market information. Estimates of future cash flows are based on a number of factors including the historical operating results, known trends, and market/economic conditions that may affect the property. To the extent acquired leases contain fixed rate renewal options that are below-market and determined to be material, we amortize such below-market lease value into rental income over the renewal period. As of December 31, 2019 , the weighted average amortization period for above-market leases, below-market leases, and in-place lease costs is 1.7 years, 2.8 years, and 3.5 years, respectively. The Company classifies those leases under which the Company is the lessee at lease commencement as finance or operating leases. Leases qualify as finance leases if the lease transfers ownership of the asset at the end of the lease term, the lease grants an option to purchase the asset that we are reasonably certain to exercise, the lease term is for a major part of the remaining economic life of the asset, or the present value of the lease payments exceeds substantially all of the fair value of the asset. Leases that do not qualify as finance leases are deemed to be operating leases. At lease commencement the Company records a lease liability which is measured as the present value of the lease payments and a right of use asset which is measured as the amount of the lease liability and any initial direct costs incurred. The Company applies a discount rate to determine the present value of the lease payments. If the rate implicit in the lease is known, the Company uses that rate. If the rate implicit in the lease is not known, the Company uses a discount rate reflective of the Company’s collateralized borrowing rate given the term of the lease. To determine the discount rate, the Company employs a third party specialist to develop an analysis based primarily on the observable borrowing rates of the Company, other REITs, and other corporate borrowers with long-term borrowings. On the consolidated statements of operations, operating leases are expensed through operating lease rent while financing leases are expensed through amortization and interest expense. On the consolidated balance sheet, financing leases include the amounts previously captioned "Properties under capital lease." When applicable, the Company combines the consideration for lease and non-lease components in the calculation of the value of the lease obligation and right-of-use asset. We incur a variety of costs in the development and leasing of our properties. After the determination is made to capitalize a cost, it is allocated to the specific component of a project that is benefited. Determination of when a development project is substantially complete and capitalization must cease involves a degree of judgment. The costs of land and building under development include specifically identifiable costs. The capitalized costs include, but are not limited to, pre-construction costs essential to the development of the property, development costs, construction costs, interest costs, real estate taxes, salaries and related costs and other costs incurred during the period of development. We consider a construction project as substantially completed and held available for occupancy upon the completion of tenant improvements, but no later than one year after major construction activity ceases. We cease capitalization on the portions substantially completed and occupied or held available for occupancy, and capitalize only those costs associated with the portions under construction. Properties other than Right of use assets - operating leases are depreciated using the straight-line method over the estimated useful lives of the assets. The estimated useful lives are as follows: Category Term Building (fee ownership) 40 years Building improvements shorter of remaining life of the building or useful life Building (leasehold interest) lesser of 40 years or remaining term of the lease Right of use assets - financing leases lesser of 40 years or remaining lease term Furniture and fixtures four to seven years Tenant improvements shorter of remaining term of the lease or useful life Right of use assets - operating leases are amortized over the remaining lease term. The amortization is made up of the principal amortization under the lease liability plus or minus the straight line adjustment of the operating lease rent under ASC 840. Depreciation expense (including amortization of right of use assets - financing leases) totaled $233.5 million , $242.8 million , and $365.3 million for the years ended December 31, 2019 , 2018 and 2017 , respectively. On a periodic basis, we assess whether there are any indications that the value of our real estate properties may be impaired or that their carrying value may not be recoverable. A property's value is considered impaired if management's estimate of the aggregate future cash flows (undiscounted) to be generated by the property is less than the carrying value of the property. To the extent impairment has occurred, the loss will be measured as the excess of the carrying amount of the property over the calculated fair value of the property. We also evaluate our real estate properties for impairment when a property has been classified as held for sale. Real estate assets held for sale are valued at the lower of their carrying value or fair value less costs to sell and depreciation expense is no longer recorded. We recognized $4.5 million , $6.8 million , and $20.3 million of rental revenue for the years ended December 31, 2019 , 2018 , and 2017 , respectively, for the amortization of aggregate below-market leases in excess of above-market leases, resulting from the allocation of the purchase price of the applicable properties. We recognized no reduction to interest expense from the amortization of above-market rate mortgages assumed for the years ended December 31, 2019 and 2018 . We recognized $0.8 million as a reduction to interest expense from the amortization of above-market rate mortgages for the year ended December 31, 2017 . The following summarizes our identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases) as of December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Identified intangible assets (included in other assets): Gross amount $ 255,198 $ 266,540 Accumulated amortization (228,223 ) (241,040 ) Net (1) $ 26,975 $ 25,500 Identified intangible liabilities (included in deferred revenue): Gross amount $ 282,048 $ 276,245 Accumulated amortization (249,514 ) (253,767 ) Net (1) $ 32,534 $ 22,478 (1) As of December 31, 2019 , no net intangible assets and no net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale. As of December 31, 2018 , no net intangible assets and no net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale. The estimated annual amortization of acquired above-market leases, net of acquired (below-market) leases (a component of rental revenue), for each of the five succeeding years is as follows (in thousands): 2020 $ (4,320 ) 2021 (2,748 ) 2022 (2,224 ) 2023 (1,301 ) 2024 (834 ) The estimated annual amortization of all other identifiable assets (a component of depreciation and amortization expense) including tenant improvements for each of the five succeeding years is as follows (in thousands): 2020 $ 5,183 2021 3,638 2022 2,064 2023 1,435 2024 1,040 Cash and Cash Equivalents We consider all highly liquid investments with maturity of three months or less when purchased to be cash equivalents. Restricted Cash Restricted cash primarily consists of security deposits held on behalf of our tenants, interest reserves, as well as capital improvement and real estate tax escrows required under certain loan agreements. Fair Value Measurements See Note 16, "Fair Value Measurements." Investment in Marketable Securities At acquisition, we designate a security as held-to-maturity, available-for-sale, or trading. As of December 31, 2019 , we did not have any securities designated as held-to-maturity or trading. We account for our available-for-sale securities at fair value pursuant to Accounting Standards Codification, or ASC, 820-10, with the net unrealized gains or losses reported as a component of accumulated other comprehensive income or loss. The cost of marketable securities sold and the amount reclassified out of accumulated other comprehensive income into earnings is determined using the specific identification method. Any unrealized losses that are determined to be other-than-temporary are recognized in earnings up to their credit component. At December 31, 2019 and 2018 , we held the following marketable securities (in thousands): December 31, 2019 2018 Commercial mortgage-backed securities $ 29,887 $ 28,638 Total marketable securities available-for-sale $ 29,887 $ 28,638 The cost basis of the commercial mortgage-backed securities was $27.5 million at both December 31, 2019 and 2018 . These securities mature at various times through 2035. We held no equity marketable securities at December 31, 2019 and 2018 . During the years ended December 31, 2019 and 2018 , we did not dispose of any marketable securities. During the year ended December 31, 2017 , we disposed of marketable securities for aggregate net proceeds of $55.1 million and realized a 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 account for our investments in unconsolidated joint ventures under the equity method of accounting in cases where we exercise significant influence over, but do not control, these entities and are not considered to be the primary beneficiary. We consolidate those joint ventures that we control or which are VIEs and where we are considered to be the primary beneficiary. In all these joint ventures, the rights of the joint venture partner are both protective as well as participating. Unless we are determined to be the primary beneficiary in a VIE, these participating rights preclude us from consolidating these VIE entities. These investments are recorded initially at cost, as investments in unconsolidated joint ventures, and subsequently adjusted for equity in net income (loss) and cash contributions and distributions. Equity in net income (loss) from unconsolidated joint ventures is allocated based on our ownership or economic interest in each joint venture and includes adjustments related to basis differences in accounting for the investment. When a capital event (as defined in each joint venture agreement) such as a refinancing occurs, if return thresholds are met, future equity income will be allocated at our increased economic interest. We recognize incentive income from unconsolidated real estate joint ventures as income to the extent it is earned and not subject to a clawback feature. Distributions we receive from unconsolidated real estate joint ventures in excess of our basis in the investment are recorded as offsets to our investment balance if we remain liable for future obligations of the joint venture or may otherwise be committed to provide future additional financial support. None of the joint venture debt is recourse to us. The Company has performance guarantees under a master lease at one joint venture. See Note 6, "Investments in Unconsolidated Joint Ventures." We assess our investments in unconsolidated joint ventures for recoverability, and if it is determined that a loss in value of the investment is other than temporary, we write down the investment to its fair value. We evaluate our equity investments for impairment based on the joint ventures' projected discounted cash flows. We do not believe that the values of any of our equity investments were impaired at December 31, 2019 . We may originate loans for real estate acquisition, development and construction ("ADC loans"), where we expect to receive some of the residual profit from such projects. When the risk and rewards of these arrangements are essentially the same as an investor or joint venture partner, we account for these arrangements as real estate investments under the equity method of accounting for investments. Otherwise, we account for these arrangements consistent with the accounting for our debt and preferred equity investments. Deferred Lease Costs Deferred lease costs consist of incremental fees and direct costs that would not have been incurred if the lease had not been obtained and are amortized on a straight-line basis over the related lease term. Certain of our employees provide leasing services to the wholly-owned properties. For the years ended December 31, 2019 , 2018 and 2017 , $6.3 million , $15.7 million , and $16.4 million of their compensation, respectively, was capitalized and is amortized over an estimated average lease term of eight years . Deferred Financing Costs Deferred financing costs represent commitment fees, legal, title and other third party costs associated with obtaining commitments for financing which result in a closing of such financing. These costs are amortized over the terms of the respective agreements. Unamortized deferred financing costs are expensed when the associated debt is refinanced or repaid before maturity. Costs incurred in seeking financing transactions, which do not close, are expensed in the period in which it is determined that the financing will not close. Deferred financing costs related to a recognized debt liability are presented in the consolidated balance sheet as a direct deduction from the carrying amount of that debt liability. Revenue Recognition Rental revenue for operating leases is recognized on a straight-line basis over the term of the lease. Rental revenue recognition commences when the leased space is substantially ready for its intended use. To determine whether the leased space is substantially ready for its intended use, management evaluates whether we are or the tenant is the owner of tenant improvements for accounting purposes. When management concludes that we are the owner of tenant improvements, rental revenue recognition begins when the tenant takes possession of the finished space, which is when such tenant improvements are substantially complete. In certain instances, when management concludes that we are not the owner of tenant improvements, rental revenue recognition begins when the tenant takes possession of or controls the space. When management concludes that we are the owner of tenant improvements for accounting purposes, we record amounts funded to construct the tenant improvements as a capital asset. For these tenant improvements, we record amounts reimbursed by tenants as a reduction of the capital asset. When management concludes that the tenant is the owner of tenant improvements for accounting purposes, we record our contribution towards those improvements as a lease incentive, which is included in deferred costs, net on our consolidated balance sheets and amortized as a reduction to rental revenue on a straight-line basis over the term of the lease. The excess of rents recognized over amounts contractually due pursuant to the underlying leases are included in deferred rents receivable on the consolidated balance sheets. In addition to base rent, our tenants also generally will pay variable rent which represents their pro rata share of increases in real estate taxes and operating expenses for the building over a base year. In some leases, in lieu of paying additional rent based upon increases in building operating expenses, the tenant will pay additional rent based upon increases in the wage rate paid to porters over the porters' wage rate in effect during a base year or increases in the consumer price index over the index value in effect during a base year. In addition, many of our leases contain fixed percentage increases over the base rent to cover escalations. Electricity is most often supplied by the landlord either on a sub-metered basis, or rent inclusion basis (i.e., a fixed fee is included in the rent for electricity, which amount may increase based upon increases in electricity rates or increases in electrical usage by the tenant). Base building services other than electricity (such as heat, air conditioning and freight elevator service during business hours, and base building cleaning) are typically provided at no additional cost, with the tenant paying additional rent only for services which exceed base building services or for services which are provided outside normal business hours. These escalations are based on actual expenses incurred in the prior calendar year. If the expenses in the current year are different from those in the prior year, then during the current year, the escalations will be adjusted to reflect the actual expenses for the current year. Rental revenue is recognized if collectability is probable. If collectability of substantially all of the lease payments is assessed as not probable, any difference between the rental revenue recognized to date and the lease payments that have been collected is recognized as a current-period adjustment to rental revenue. A subsequent change in the assessment of collectability to probable may result in a current-period adjustment to rental revenue for any difference between the rental revenue that would have been recognized if collectability had always been assessed as probable and the rental revenue recognized to date. The Company provides its tenants with certain customary services for lease contracts such as common area maintenance and general security. We have elected to combine the nonlease components with the lease components of our operating lease agreements and account for them as a single lease component in accordance with ASC 842. We record a gain or loss on sale of real estate assets when we no longer hold a controlling financial interest in the entity holding the real estate, a contract exists with a third party and that third party has control of the assets acquired. Investment income on debt and preferred equity investments is accrued based on the contractual terms of the instruments and when, in the opinion of management, it is deemed collectible. Some debt and preferred equity investments provide for accrual of interest at specified rates, which differ from current payment terms. Interest is recognized on such loans at the accrual rate subject to management's determination that accrued interest is collectible. If management cannot make this determination, interest income above the current pay rate is recognized only upon actual receipt. Deferred origination fees, original issue discounts and loan origination costs, if any, are recognized as an adjustment to interest income over the terms of the related investments using the effective interest method. Fees received in connection with loan commitments are also deferred until the loan is funded and are then recognized over the term of the loan as an adjustment to yield. Discounts or premiums associated with the purchase of loans are amortized or accreted into interest income as a yield adjustment on the effective interest method based on expected cash flows through the expected maturity date of the related investment. If we purchase a debt or preferred equity investment at a discount, intend to hold it until maturity and expect to recover the full value of the investment, we accrete the discount into income as an adjustment to yield over the term of the investment. If we purchase a debt or preferred equity investment at a discount with the intention of foreclosing on the collateral, we do not accrete the discount. For debt investments acquired at a discount for credit quality, the difference between contractual cash flows and expected cash flows at acquisition is not accreted. Anticipated exit fees, the collection of which is expected, are also recognized over the term of the loan as an adjustment to yield. Debt and preferred equity investments are placed on a non-accrual status at the earlier of the date at which payments become 90 days past due or when, in the opinion of management, a full recovery of interest income becomes doubtful. Interest income recognition on any non-accrual debt or preferred equity investment is resumed when such non-accrual debt or preferred equity investment becomes contractually current and performance is demonstrated to be resumed. Interest is recorded as income on impaired loans only to the extent cash is received. We may syndicate a portion of the loans that we originate or sell the loans individually. When a transaction meets the criteria for sale accounting, we recognize gain or loss based on the difference between the sales price and the carrying value of the loan sold. Any related unamortized deferred origination fees, original issue discounts, loan origination costs, discounts or premiums at the time of sale are recognized as an adjustment to the gain or loss on sale, which is included in investment income on the consolidated statement of operations. Any fees received at the time of sale or syndication are recognized as part of investment income. Asset management fees are recognized on a straight-line basis over the term of the asset management agreement. Allowance for Loan Loss and Other Investment Reserves The expense for loan loss and other investment reserves in connection with debt and preferred equity investments is the charge to earnings to adjust the allowance for possible losses to the level that we estimate to be adequate, based on Level 3 data, considering delinquencies, loss experience and collateral quality. The Company evaluates debt and preferred equity investments that are classified as held to maturity for possible impairment or credit deterioration associated with the performance and/or value of the underlying collateral property as well as the financial and operating capability of the borrower/sponsor. Quarterly, the Company assigns each loan a risk rating. Based on a 3-point scale, loans are rated “1” through “3,” from less risk to greater risk, which ratings are defined as follows: 1 - Low Risk Assets - Low probability of loss, 2 - Watch List Assets - Higher potential for loss, 3 - High Risk Assets - Loss more likely than not. When it is probable that we will be unable to collect all amounts contractually due, the investment is considered impaired. A valuation allowance is measured based upon the excess of the carrying value of the investment over the fair value of the collateral. Any deficiency between the carrying value of an asset and the calculated value of the collateral is charged to expense. We continue to assess or adjust our estimates based on circumstances of a loan and the underlying collateral. If additional information reflects increased recovery of our investment, we will adjust our reserves accordingly. Debt and preferred equity investments that are classified as held for sale are carried at the lower of cost or fair market value using available market information obtained through consultation with dealers or other originators of such investments as well as discounted cash flow models based on Level 3 data pursuant to ASC 820-10. As circumstances change, management may conclude not to sell an investment designated as held for sale. In such situations, the investment will be reclassified at its net carrying value to debt and preferred equity investments held to maturity. For these reclassified investments, the difference between the current carrying value and the expected cash to be collected at maturity will be accreted into income over the remaining term of the investment. Rent Expense Rent expense is recognized on a straight-line basis over the initial term of the lease. The excess of the rent expense recognized over the amounts contractually due pursuant to the underlying lease is included in the lease liability - operating leases on the consolidated balance sheets. Underwriting Commissions and Costs Underwriting commissions and costs incurred in connection with our stock offerings are reflected as a reduction of additional paid-in-capital. Exchangeable Debt Instruments The initial proceeds from exchangeable debt that may be settled in cash, including partial cash settlements, are bifurcated between a liability component and an equity component associated with the embedded conversion option. The objective of the accounting guidance is to require the liability and equity components of exchangeable debt to be separately accounted for in a manner such that the interest expense on the exchangeable debt is not recorded at the stated rate of interest but rather at an effective rate that reflects the issuer's conventional debt borrowing rate at the date of issuance. We calculate the liability component of exchangeable debt based on the present value of the contractual cash flows discounted at our comparable market conventional debt borrowing rate at the date of issuance. The difference between the principal amount and the fair value of the liability component is reported as a discount on the exchangeable debt that is accreted as additional interest expense from the issuance date through the contractual maturity date using the effective interest method. A portion of this additional interest expense may be capitalized to the development and redevelopment balances qualifying for interest capitalization each period. The liability component of the exchangeable debt is reported net of discounts on our consolidated balance sheets. We calculate the equity component of exchangeable debt based on the difference between the initial proceeds received from the issuance of the exchangeable debt and the fair value of the liability component at the issuance date. The equity component is included in additional paid-in-capital, net of issuance costs, on our consolidated balance sheets. We allocate issuance costs for exchangeable debt between the liability and the equity components based on their relative values. Transaction Costs Transaction costs for asset acquisitions are capitalized to the investment basis, which is then subject to a purchase price allocation based on relative fair value. Transaction costs for business combinations or costs incurred on potential transactions that are not consummated are expensed as incurred. Income Taxes SL Green is taxed as a REIT under Section 856(c) of the Code. As a REIT, SL Green generally is not subject to Federal income tax. To maintain its qualification as a REIT, SL Green must distribute at least 90% of its REIT taxable income to its stockholders and meet certain other requirements. If SL Green fails to qualify as a REIT in any taxable year, SL Green will be subject to Federal income tax on its taxable income at regular corporate rates. SL Green may also be subject to certain state, local and franchise taxes. Under certain circumstances, Federal income and excise taxes may be due on its undistributed taxable income. The Operating Partnership is a partnership and, as a result, all income and losses of the partnership are allocated to the partners for inclusion in their respective income tax returns. The only provision for in

Property Acquisitions

Property Acquisitions	12 Months Ended
	Dec. 31, 2019
Business Combinations [Abstract]
Property Acquisitions	Property Acquisitions 2019 Acquisitions The following table summarizes the properties acquired during the year ended December 31, 2019 : Property Acquisition Date Property Type Approximate Square Feet Gross Asset Valuation (in millions) 106 Spring Street (1) April 2019 Fee Interest 5,928 $ 80.2 410 Tenth Avenue (2) May 2019 Fee Interest 638,000 440.0 110 Greene Street (3) May 2019 Fee Interest 223,600 256.5 (1) In April 2019, the Company accepted an assignment of the equity interests in the property in lieu of repayment of the Company's debt investment and marked the assets received and liabilities assumed to fair value. (2) In May 2019, the Company closed on the acquisition of a majority and controlling 70.87% interest in 410 Tenth Avenue. We recorded the assets acquired and liabilities assumed at fair value, which resulted in the recognition of a fair value adjustment of $67.6 million, which is reflected in the Company's consolidated statement of operations within purchase price and other fair value adjustments, and $18.3 million of net intangible lease liabilities. (3) In May 2019, the Company acquired from our joint venture partner the remaining 10% interest in this property that the Company did not already own. 2018 Acquisitions The following table summarizes the properties acquired during the year ended December 31, 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 1231 Third Avenue (2)(3) July 2018 Fee Interest 39,000 55.4 Upper East Side Residential (3)(4) August 2018 Fee Interest 0.2 acres 30.2 133 Greene Street (2) October 2018 Fee Interest 6,425 31.0 712 Madison Avenue (2) December 2018 Fee Interest 6,600 58.0 (1) In May 2018, the Company was the successful bidder at the foreclosure of the asset. We recorded the assets acquired and liabilities assumed at fair value. This resulted in the recognition of a fair value adjustment of $8.1 million , which is reflected in the Company's consolidated statement of operations within purchase price and other fair value adjustments. See Note 16, "Fair Value Measurements." The Company subsequently sold a 49% interest in the property in November 2018. See Note 4, "Properties Held for Sale and Dispositions." and Note 6, "Investments in Unconsolidated Joint Ventures." (2) The Company accepted an assignment of the equity interests in the property in lieu of repayment of the Company's debt investment, and recorded the assets received and liabilities assumed at fair value. (3) This property was subsequently sold in October 2018. See Note 4, "Properties Held for Sale and Dispositions." (4) In August 2018, the Company acquired the fee interest in three additional land parcels at the Upper East Side Residential Assemblage. 2017 Acquisitions

Properties Held for Sale and Pr

Properties Held for Sale and Property Dispositions	12 Months Ended
	Dec. 31, 2019
Discontinued Operations and Disposal Groups [Abstract]
Properties Held for Sale and Property Dispositions	Properties Held for Sale During the third quarter of 2019, we entered into an agreement to sell 220 East 42nd Street in Manhattan for a total consideration of $815.0 million . The sale is expected to close in the first quarter of 2020. As of December 31, 2019 , 220 East 42nd Street was classified as held for sale. Property Dispositions The following table summarizes the properties sold during the years ended December 31, 2019 , 2018 , and 2017 : Property Disposition Date Property Type Unaudited Approximate Usable Square Feet Sales Price (1) (in millions) Gain (Loss) on Sale (2) (in millions) Suburban Properties (3) December 2019 Fee Interest 1,107,000 $ 229.2 $ 1.8 1640 Flatbush Avenue December 2019 Fee Interest 1,000 16.2 5.5 562 Fifth Avenue December 2019 Fee Interest 42,635 52.4 (26.6 ) 1010 Washington Boulevard November 2019 Fee Interest 143,400 23.1 (7.1 ) 115 Spring Street (4) August 2019 Fee Interest 5,218 66.6 3.6 2 Herald Square (5) November 2018 Office/Retail 369,000 265.0 — 400 Summit Lake Drive November 2018 Land 39.5 acres 3.0 (36.2 ) Upper East Side Assemblage (6)(7) October 2018 Development 70,142 143.8 (6.3 ) 1-6 International Drive July 2018 Office 540,000 55.0 (2.6 ) 635 Madison Avenue June 2018 Retail 176,530 153.0 (14.1 ) 115-117 Stevens Avenue May 2018 Office 178,000 12.0 (0.7 ) 600 Lexington Avenue January 2018 Office 303,515 305.0 23.8 1515 Broadway (8) December 2017 Office 1,750,000 1,950.0 — 125 Chubb Way October 2017 Office 278,000 29.5 (26.1 ) 16 Court Street October 2017 Office 317,600 171.0 64.9 680-750 Washington Boulevard July 2017 Office 325,000 97.0 (44.2 ) 520 White Plains Road April 2017 Office 180,000 21.0 (14.6 ) 102 Greene Street (9) April 2017 Retail 9,200 43.5 4.9 (1) Sales price represents the gross sales price for a property or the gross asset valuation for interests in a property. (2) The gain on sale for 1640 Flatbush Avenue, 600 Lexington Avenue, 16 Court Street, and 102 Greene Street are net of $2.0 million , $1.3 million , $2.5 million , and $0.9 million , respectively, in employee compensation accrued in connection with the realization of these investment gains. Additionally, amounts do not include adjustments for expenses recorded in subsequent periods. (3) Suburban Properties consists of 360 Hamilton Avenue, 100 Summit Lake Drive, 200 Summit Lake Drive, and 500 Summit Lake Drive. (4) The Company sold a 49% interest, which resulted in the deconsolidation of our remaining 51% interest. We recorded our investment at fair value which resulted in the recognition of a fair value adjustment of $3.8 million , which is reflected in the Company's consolidated statements of operations within purchase price and other fair value adjustments. See Note 6, "Investments in Unconsolidated Joint Ventures." (5) In November 2018, the Company sold a 49% interest in 2 Herald Square to an Israeli institutional investor. See Note 6, "Investments in Unconsolidated Joint Ventures." (6) Upper East Side Assemblage consists of 260 East 72nd Street, 31,076 square feet of development rights, 252-254 East 72nd Street, 257 East 71st Street, 259 East 71st Street, and 1231 Third Avenue. (7) The Company recorded a $5.8 million charge in 2018 that is included in depreciable real estate reserves and impairment in the consolidated statement of operations. (8) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. At that time, the sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. See Note 6, "Investments in Unconsolidated Joint Ventures." (9) In April 2017, we closed on the sale of a 90% interest in 102 Greene Street and accounted for our retained 10% interest in the property as an investment in unconsolidated joint ventures. We sold the remaining 10% interest in September 2017. See Note 6, "Investments in Unconsolidated Joint Ventures."

Debt and Preferred Equity Inves

Debt and Preferred Equity Investments	12 Months Ended
	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Debt and Preferred Equity Investments	Debt and Preferred Equity Investments Below is a summary of the activity relating to our debt and preferred equity investments as of December 31, 2019 and 2018 (in thousands): December 31, 2019 December 31, 2018 Balance at beginning of year (1) $ 2,099,393 $ 2,114,041 Debt investment originations/accretion (2) 652,866 834,304 Preferred equity investment originations/accretion (2) 14,736 151,704 Redemptions/sales/syndications/amortization (3) (1,190,689 ) (994,906 ) Net change in loan loss reserves 4,000 (5,750 ) Balance at end of period (1) $ 1,580,306 $ 2,099,393 (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, but did not meet the conditions for sale accounting, are included in other assets and other liabilities on the consolidated balance sheets. Below is a summary of the balances relating to our debt and preferred equity investments as of December 31, 2019 (dollars in thousands): Floating Rate Fixed Rate Total Carrying Value Senior Financing Maturity Type Carrying Value Face Value Interest Rate Carrying Value Face Value Interest Rate Senior Mortgage Debt $ 341,513 $342,861 L + 2.75 - 5.50% $ 1,010 $1,250 3.00% $ 342,523 $ — 2020-2022 Junior Mortgage Debt 31,960 32,000 L + 6.00 - 7.25% — — — $ 31,960 100,000 2020-2021 Mezzanine Debt 245,412 247,385 L + 4.60 - 12.36% 721,175 728,138 2.90 - 10.00% $ 966,587 5,188,939 2020-2029 Preferred Equity — — — 239,236 244,983 7.00 - 11.00% $ 239,236 272,000 2020-2023 Balance at end of period $ 618,885 $ 622,246 — $ 961,421 $ 974,371 — $ 1,580,306 $ 5,560,939 — The following table is a rollforward of our total loan loss reserves at December 31, 2019 , 2018 and 2017 (in thousands): December 31, 2019 2018 2017 Balance at beginning of year $ 5,750 $ — $ — Expensed — 6,839 — Recoveries — — — Charge-offs and reclassifications (4,000 ) (1,089 ) — Balance at end of period $ 1,750 $ 5,750 $ — At December 31, 2019 , all debt and preferred equity investments were performing in accordance with their respective terms. At December 31, 2019 , the Company's loan loss reserves of 1.8 million were attributable to one investment with an unpaid principal balance of $142.9 million that is being marketed for sale, but is otherwise performing in accordance with its respective terms, and was not put on nonaccrual. At December 31, 2018 , all debt and preferred equity investments were performing in accordance with their respective terms. At December 31, 2018 , the Company's loan loss reserves of $5.8 million were attributable to two investments with an unpaid principal balance of $159.9 million that were being marketed for sale, were performing in accordance with their respective terms, and were not put on nonaccrual. We have determined that we have one portfolio segment of financing receivables at December 31, 2019 and 2018 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 $131.1 million and $124.5 million at December 31, 2019 and 2018 , respectively. No financing receivables were 90 days past due at December 31, 2019 with the exception of a $28.4 million financing receivable which was put on nonaccrual in August 2018 as a result of interest default. The loan was evaluated in accordance with our loan review procedures and the Company concluded that the fair value of the collateral exceeded the carrying amount of the loan. As of December 31, 2019 , management estimated the weighted average risk rating for our debt and preferred equity investments to be 1.2 . Debt Investments As of December 31, 2019 and 2018 , we held the following debt investments with an aggregate weighted average current yield of 8.42% , at December 31, 2019 (in thousands): Loan Type December 31, 2019 Future Funding Obligations December 31, 2019 Senior Financing December 31, 2019 Carrying Value (1) December 31, 2018 Carrying Value (1) Maturity Date (2) Fixed Rate Investments: Mezzanine Loan (3a) $ — $ 1,160,000 $ 222,775 $ 213,185 March 2020 Mezzanine Loan — 15,000 3,500 3,500 September 2021 Mezzanine Loan — 147,000 24,952 24,932 April 2022 Mezzanine Loan — 280,000 38,734 36,585 August 2022 Mezzanine Loan — 326,574 215,737 — June 2023 Mezzanine Loan — 83,790 12,714 12,706 November 2023 Mezzanine Loan — 180,000 30,000 30,000 December 2023 Mezzanine Loan (3b) — 115,000 12,950 12,941 June 2024 Mezzanine Loan — 95,000 30,000 30,000 January 2025 Mezzanine Loan — 1,712,750 55,250 55,250 June 2027 Mezzanine Loan — — — 11,000 Total fixed rate $ — $ 4,115,114 $ 646,612 $ 430,099 Floating Rate Investments: Mortgage/Mezzanine Loan (4) $ 2,509 $ 29,420 $ 82,696 $ 62,493 January 2020 Mortgage/Mezzanine Loan — — 69,839 — March 2020 Junior Mortgage Loan — 40,000 20,000 19,986 April 2020 Mezzanine Loan 4,831 47,302 15,743 12,627 July 2020 Mortgage/Mezzanine Loan — — 19,971 19,999 August 2020 Mortgage Loan 44,737 — 106,473 88,501 September 2020 Mortgage/Mezzanine Loan — 63,990 55,573 83,449 October 2020 Mezzanine Loan 19,212 421,938 51,387 88,817 December 2021 Mortgage/Mezzanine Loan — — 35,386 35,266 December 2020 Mortgage/Mezzanine Loan (3c) 10,384 — 96,570 277,694 April 2021 Mezzanine Loan — 275,000 49,809 24,961 April 2021 Junior Mortgage Participation/Mezzanine Loan — 60,000 15,698 15,665 July 2021 Mezzanine Loan 12,999 151,175 41,395 — July 2021 Mezzanine Loan 44,000 — 13,918 — December 2022 Mezzanine Loan — 85,000 20,000 — December 2029 Mezzanine Loan — — — 53,402 Mezzanine Loan — — — 79,164 Mezzanine Loan — — — 15,333 Loan Type December 31, 2019 Future Funding Obligations December 31, 2019 Senior Financing December 31, 2019 Carrying Value (1) December 31, 2018 Carrying Value (1) Maturity Date (2) Mezzanine Loan — — — 14,822 Mortgage/Mezzanine Loan — — — 154,070 Mezzanine Loan — — — 34,886 Mortgage/Junior Mortgage Participation Loan — — — 84,012 Mortgage/Mezzanine Loan — — — 37,094 Mortgage/Mezzanine Loan — — — 98,804 Mezzanine Loan — — — 7,305 Mezzanine Loan — — — 14,998 Mezzanine Loan — — — 21,990 Mezzanine Loan (5) — — — 37,499 Total floating rate $ 138,672 $ 1,173,825 $ 694,458 $ 1,382,837 Total $ 138,672 $ 5,288,939 $ 1,341,070 $ 1,812,936 (1) Carrying value is net of discounts, premiums, original issue discounts and deferred origination fees. (2) Represents contractual maturity, excluding any unexercised extension options. (3) Carrying value is net of the following amounts that were sold or syndicated, which are included in other assets and other liabilities on the consolidated balance sheets as a result of the transfers not meeting the conditions for sale accounting: (a) $1.3 million , (b) $12.0 million and (c) $96.4 million (4) This loan was extended in January 2020. (5) In 2019, the Company accepted an assignment of the equity interests in the property in-lieu of repayment and marked the assets received and liabilities assumed to fair value. Preferred Equity Investments As of December 31, 2019 and 2018 , we held the following preferred equity investments with an aggregate weighted average current yield of 9.63% at December 31, 2019 (in thousands): Type December 31, 2019 Future Funding Obligations December 31, 2019 December 31, 2019 (1) December 31, 2018 (1) Mandatory Redemption (2) Preferred Equity $ — $ 272,000 $ 141,171 $ 143,183 April 2021 Preferred Equity — 1,763,529 98,065 143,274 June 2022 Total $ — $ 2,035,529 $ 239,236 $ 286,457 (1) Carrying value is net of deferred origination fees. (2) Represents contractual maturity, excluding any unexercised extension options.

Investments in Unconsolidated J

Investments in Unconsolidated Joint Ventures	12 Months Ended
	Dec. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Investments in Unconsolidated Joint Ventures	Investments in Unconsolidated Joint Ventures We have investments in several real estate joint ventures with various partners. As of December 31, 2019 , the book value of these investments was 2.9 billion , net of investments with negative book values totaling $80.9 million for which we have an implicit commitment to fund future capital needs. As of December 31, 2019 , 800 Third Avenue, 21 East 66th Street, 605 West 42nd Street, 333 East 22nd Street, and certain properties within the Stonehenge Portfolio are VIEs in which we are not the primary beneficiary. As of December 31, 2018 , 800 Third Avenue, 21 East 66th Street, 605 West 42nd Street, 333 East 22nd Street, One Vanderbilt, and certain properties within the Stonehenge Portfolio are VIEs in which we are not the primary beneficiary. Our net equity investment in these VIEs was $145.9 million as of December 31, 2019 and $808.3 million as of December 31, 2018 . Our maximum loss is limited to the amount of our equity investment in these VIEs. See the "Principles of Consolidation" section of Note 2, "Significant Accounting Policies". All other investments below are voting interest entities. As we do not control the joint ventures listed below, we account for them under the equity method of accounting. The table below provides general information on each of our joint ventures as of December 31, 2019 : Property Partner Ownership Interest (1) Economic Interest (1) Unaudited Approximate Square Feet 100 Park Avenue Prudential Real Estate Investors 49.90% 49.90% 834,000 717 Fifth Avenue Jeff Sutton/Private Investor 10.92% 10.92% 119,500 800 Third Avenue Private Investors 60.52% 60.52% 526,000 919 Third Avenue (2) New York State Teacher's Retirement System 51.00% 51.00% 1,454,000 11 West 34th Street Private Investor/Jeff Sutton 30.00% 30.00% 17,150 280 Park Avenue Vornado Realty Trust 50.00% 50.00% 1,219,158 1552-1560 Broadway (3) Jeff Sutton 50.00% 50.00% 57,718 10 East 53rd Street Canadian Pension Plan Investment Board 55.00% 55.00% 354,300 21 East 66th Street (4) Private Investors 32.28% 32.28% 13,069 650 Fifth Avenue (5) Jeff Sutton 50.00% 50.00% 69,214 121 Greene Street Jeff Sutton 50.00% 50.00% 7,131 55 West 46th Street Prudential Real Estate Investors 25.00% 25.00% 347,000 Stonehenge Portfolio (6) Various Various Various 1,439,016 605 West 42nd Street The Moinian Group 20.00% 20.00% 927,358 11 Madison Avenue PGIM Real Estate 60.00% 60.00% 2,314,000 333 East 22nd Street Private Investors 33.33% 33.33% 26,926 400 East 57th Street (7) BlackRock, Inc and Stonehenge Partners 51.00% 41.00% 290,482 One Vanderbilt National Pension Service of Korea/Hines Interest LP 71.01% 71.01% — Worldwide Plaza RXR Realty / New York REIT / Private Investor 24.35% 24.35% 2,048,725 1515 Broadway Allianz Real Estate of America 56.87% 56.87% 1,750,000 2 Herald Square Israeli Institutional Investor 51.00% 51.00% 369,000 115 Spring Street Private Investor 51.00% 51.00% 5,218 (1) Ownership interest and economic interest represent the Company's interests in the joint venture as of December 31, 2019 . Changes in ownership or economic interests within the current year are disclosed in the notes below. (2) 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. We recorded our 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 joint venture. (3) The acquisition 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. (4) We hold a 32.28% interest in three retail and one residential units at the property and a 16.14% interest in three residential units at the property. (5) 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. (6) We, together with our joint venture partner, closed on the sale of one property from the Stonehenge Portfolio in February 2019 and another property in May 2019. These sales are further described under Sale of Joint Venture Interest of Properties below. (7) In October 2016, we sold a 49% interest in this property. Our 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. Our joint venture with Stonehenge remains consolidated resulting in the combined 51% interest being shown within investments in unconsolidated joint ventures on our balance sheet. Acquisition, Development and Construction Arrangements Based on the characteristics of the following arrangements, which are similar to those of an investment, combined with the expected residual profit of not greater than 50% , we have accounted for these debt and preferred equity investments under the equity method. As of December 31, 2019 and 2018 , the carrying value for acquisition, development and construction arrangements were as follows (dollars in thousands): Loan Type December 31, 2019 December 31, 2018 Maturity Date Mezzanine Loan $ — 44,357 $ — $ 44,357 Disposition of Joint Venture Interests or Properties The following table summarizes the investments in unconsolidated joint ventures sold during the years ended December 31, 2019 , 2018 , and 2017 : Property Ownership Interest Sold Disposition Date Gross Asset Valuation (in thousands) (1) Gain (Loss) on Sale (in thousands) (2) 21 East 66th Street (3) 1 residential unit December 2019 $ 2,900 $ 279 521 Fifth Avenue 50.50% May 2019 381,000 57,874 131-137 Spring Street 20.00% January 2019 216,000 17,660 Stonehenge Portfolio (partial) Various Various - 2019 468,800 (2,408 ) 3 Columbus Circle 48.90% November 2018 851,000 160,368 Mezzanine Loan (4) 33.33% August 2018 15,000 N/A 724 Fifth Avenue 49.90% July 2018 365,000 64,587 Jericho Plaza 11.67% June 2018 117,400 147 1745 Broadway 56.87% May 2018 633,000 52,038 175-225 Third Street Brooklyn, New York 95.00% April 2018 115,000 19,483 1515 Broadway (5) 13.00% February 2018 1,950,000 — Stonehenge Portfolio (partial) Various Various - 2018 331,100 (6,063 ) 102 Greene Street 10.00% September 2017 43,500 283 76 11th Avenue (6) 33.33% May 2017 138,240 N/A Stonehenge Portfolio (partial) Various March 2017 300,000 871 (1) Represents implied gross valuation for the joint venture or sales price of the property. (2) Represents the Company's share of the gain or (loss). The gain on sale is net of $4.0 million , $11.7 million , and $0 of employee compensation accrued in connection with the realization of these investment gains in the years ended December 31, 2019 , 2018 , and 2017 , respectively. Additionally, gain (loss) amounts do not include adjustments for expenses recorded in subsequent periods. (3) We, together with our joint venture partner, closed on the sale of one residential unit at the property. (4) Our investment in a joint venture that owned a mezzanine loan secured by a commercial property in midtown Manhattan was repaid after the joint venture received repayment of the underlying loan. (5) Our investment in 1515 Broadway was marked to fair value on January 1, 2018 upon adoption of ASC 610-20. (6) Our investment in a joint venture that owned two mezzanine notes secured by interests in the entity that owns 76 11th Avenue was repaid after the joint venture received repayment of the underlying loans. In May 2017, we recognized a gain of $13.0 million related to the sale in May 2014 of our ownership interest in 747 Madison Avenue. The sale did not meet the criteria for sale accounting in May of 2014 and, therefore, remained on our consolidated financial statements. The sale criteria was met in May of 2017 resulting in recognition of the deferred gain on the sale. Joint Venture Mortgages and Other Loans Payable We generally finance our joint ventures with non-recourse debt. In certain cases we may provide guarantees or master leases for tenant space, which terminate upon the satisfaction of specified circumstances or repayment of the underlying loans. The mortgage notes and other loans payable collateralized by the respective joint venture properties and assignment of leases at December 31, 2019 and 2018 , respectively, are as follows (dollars in thousands): Property Economic Interest (1) Maturity Date Interest Rate (2) December 31, 2019 December 31, 2018 Fixed Rate Debt: 717 Fifth Avenue (mortgage) 10.92 % July 2022 4.45% $ 300,000 $ 300,000 717 Fifth Avenue (mezzanine) 10.92 % July 2022 5.50% 355,328 355,328 650 Fifth Avenue (mortgage) 50.00 % October 2022 4.46% 210,000 210,000 650 Fifth Avenue (mezzanine) 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% 500,000 500,000 1515 Broadway 56.87 % March 2025 3.93% 838,546 855,876 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% 97,735 99,828 Worldwide Plaza 24.35 % November 2027 3.98% 1,200,000 1,200,000 Stonehenge Portfolio (3) Various Various 3.50% 196,112 321,076 521 Fifth Avenue (4) — 170,000 Total fixed rate debt $ 5,351,721 $ 5,666,108 Floating Rate Debt: 10 East 53rd Street (5) 55.00 % February 2020 L+ 2.25% $ 170,000 $ 170,000 280 Park Avenue 50.00 % September 2020 L+ 1.73% 1,200,000 1,200,000 1552 Broadway 50.00 % October 2020 L+ 2.65% 195,000 195,000 121 Greene Street 50.00 % November 2020 L+ 1.50% 15,000 15,000 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% 356,972 360,000 One Vanderbilt (6) 71.01 % September 2021 L+ 2.50% 732,928 375,000 2 Herald Square 51.00 % November 2021 L+ 1.45% 190,000 133,565 55 West 46th Street (7) 25.00 % August 2022 L+ 1.25% 192,524 185,569 115 Spring Street 51.00 % September 2023 L+ 3.40% 65,550 — 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% 712 1,571 131-137 Spring Street (8) — 141,000 103 East 86th Street (9) — 38,000 Total floating rate debt $ 3,691,686 $ 3,387,705 Total joint venture mortgages and other loans payable $ 9,043,407 $ 9,053,813 Deferred financing costs, net (91,538 ) (103,191 ) Total joint venture mortgages and other loans payable, net $ 8,951,869 $ 8,950,622 (1) Economic interest represents the Company's interests in the joint venture as of December 31, 2019 . 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 December 31, 2019 , 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) Amount is comprised of $132.6 million and $63.5 million in fixed-rate mortgages that mature in April 2028 and July 2029, respectively. (4) In May 2019, we, together with our joint venture partner, closed on the sale of the property. (5) This loan was refinanced in February 2020. (6) This loan is a $1.75 billion construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial five year term with two one year extension options. Advances under the loan are subject to incurred costs, funded equity, loan to value thresholds, and entering into construction contracts. (7) In August 2019, this loan was refinanced with a new $192.5 million mortgage loan. This loan has a committed amount of $198.0 million, of which $5.5 million was unfunded as of December 31, 2019. (8) In January 2019, we closed on the sale of our interest in the property. (9) In February 2019, we, together with our joint venture partner, closed on the sale of the property. We are entitled to receive fees for providing management, leasing, construction supervision and asset management services to certain of our joint ventures. We earned $13.0 million , $14.2 million and $22.6 million from these services, net of our ownership share of the joint ventures, for the years ended December 31, 2019 , 2018 , and 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 December 31, 2019 and 2018 , are as follows (unaudited, in thousands): December 31, 2019 December 31, 2018 Assets (1) Commercial real estate property, net $ 14,349,628 $ 14,347,673 Cash and restricted cash 336,189 381,301 Tenant and other receivables and deferred rents receivable 371,065 273,141 Debt and preferred equity investments, net — 44,357 Other assets 2,039,429 2,187,166 Total assets $ 17,096,311 $ 17,233,638 Liabilities and equity (1) Mortgages and other loans payable, net $ 8,951,869 $ 8,950,622 Deferred revenue/gain 1,501,616 1,660,838 Lease liabilities 897,380 637,168 Other liabilities 308,304 309,145 Equity 5,437,142 5,675,865 Total liabilities and equity $ 17,096,311 $ 17,233,638 Company's investments in unconsolidated joint ventures $ 2,912,842 $ 3,019,020 (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. In addition, at December 31, 2019, $133.1 million of net unamortized basis differences between the amount at which our investments are carried and our share of equity in net assets of the underlying property will be amortized through equity in net income (loss) from unconsolidated joint ventures over the remaining life of the underlying items having given rise to the differences. The combined statements of operations for the unconsolidated joint ventures, from acquisition date through the years ended December 31, 2019 , 2018 , and 2017 are as follows (unaudited, in thousands): Year Ended December 31, 2019 2018 2017 Total revenues $ 1,163,534 $ 1,244,804 $ 904,230 Operating expenses 202,881 219,440 157,610 Real estate taxes 212,355 226,961 142,774 Operating lease rent 24,816 18,697 16,794 Interest expense, net of interest income 372,408 363,055 250,063 Amortization of deferred financing costs 19,336 21,634 23,026 Transaction related costs — — 146 Depreciation and amortization 407,697 421,458 279,419 Total expenses $ 1,239,493 $ 1,271,245 $ 869,832 Loss on early extinguishment of debt (1,031 ) — (7,899 ) Net (loss) income before gain on sale (1) $ (76,990 ) $ (26,441 ) $ 26,499 Company's equity in net (loss) income from unconsolidated joint ventures (1) $ (34,518 ) $ 7,311 $ 21,892 (1) The combined statements of operations and the Company's equity in net income (loss) for the unconsolidated joint ventures reflects the effect of step ups in basis on the retained non-controlling interests in deconsolidated investments as a result of the adoption of ASC 610-20 in January 2018.

Deferred Costs

Deferred Costs	12 Months Ended
	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred Costs	Deferred Costs Deferred costs at December 31, 2019 and 2018 consisted of the following (in thousands): December 31, 2019 2018 Deferred leasing costs $ 466,136 $ 453,833 Less: accumulated amortization (260,853 ) (244,723 ) Deferred costs, net $ 205,283 $ 209,110

Mortgages and Other Loans Payab

Mortgages and Other Loans Payable	12 Months Ended
	Dec. 31, 2019
Mortgages and Other Loans Payable
Mortgages and Other Loans Payable	Mortgages and Other Loans Payable The first mortgages and other loans payable collateralized by the respective properties and assignment of leases or debt investments at December 31, 2019 and 2018 , respectively, were as follows (dollars in thousands): Property Maturity Date Interest Rate (1) December 31, 2019 December 31, 2018 Fixed Rate Debt: 762 Madison Avenue February 2022 5.00% $ 771 $ 771 100 Church Street July 2022 4.68% 209,296 213,208 420 Lexington Avenue October 2024 3.99% 299,165 300,000 400 East 58th Street (2) November 2026 3.00% 39,094 39,931 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 3.59% 35,123 35,807 315 West 33rd Street February 2027 4.17% 250,000 250,000 Total fixed rate debt $ 1,383,449 $ 1,389,717 Floating Rate Debt: FHLB Facility (4) January 2020 L+ 0.26% $ 10,000 $ — FHLB Facility (5) February 2020 L+ 0.32% 15,000 — FHLB Facility June 2020 L+ 0.17% 14,500 — 2017 Master Repurchase Agreement June 2020 L+ 2.19% 152,684 300,000 133 Greene Street August 2020 L+ 2.00% 15,523 15,523 106 Spring Street January 2021 L+ 2.50% 38,025 — 609 Fifth Avenue March 2021 L+ 2.40% 53,773 — 185 Broadway (6) November 2021 L+ 2.85% 120,110 111,869 712 Madison Avenue December 2021 L+ 1.85% 28,000 28,000 410 Tenth Avenue (7) May 2022 L+ 2.23% 330,819 — 719 Seventh Avenue September 2023 L+ 1.20% 50,000 50,000 FHLB Facility (8) — 13,000 115 Spring Street (9) — 65,550 FHLB Facility (10) — 14,500 Total floating rate debt $ 828,434 $ 598,442 Total mortgages and other loans payable $ 2,211,883 $ 1,988,159 Deferred financing costs, net of amortization (28,630 ) (26,919 ) Total mortgages and other loans payable, net $ 2,183,253 $ 1,961,240 (1) Interest rate as of December 31, 2019 , 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 $34.2 million mortgage loan and $0.9 million mezzanine 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) In January 2020, the loan was repaid and a new advance was drawn in the amount of $10.0 million with a spread of 16.5 basis points. (5) In February 2020, the loan was repaid and a new advance was drawn in the amount of $15.0 million with a spread of 26.0 basis points. (6) This loan is a $225.0 million construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial three year term with two one year extension options. Advances under the loan are subject to incurred costs and funded equity requirements. (7) This loan is a $465.0 million construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial three year term with two one year extension options. Advances under the loan are subject to incurred costs and funded equity requirements. (8) In August 2019, the loan was repaid. (9) In August 2019, the Company sold a 49% interest in the property to a private investor. The transaction resulted in the deconsolidation of our remaining 51% interest. See Note 6, "Investments in Unconsolidated Joint Ventures." (10) In December 2019, the loan was repaid. At December 31, 2019 and 2018 , the gross book value of the properties and debt and preferred equity investments collateralizing the mortgages and other loans payable was approximately $3.3 billion and $2.6 billion, respectively. Federal Home Loan Bank of New York ("FHLB") Facility The Company’s wholly-owned subsidiary, Ticonderoga Insurance Company, or Ticonderoga, a Vermont licensed captive insurance company, is a member of the Federal Home Loan Bank of New York, or FHLBNY. As a member, Ticonderoga may borrow funds from the FHLBNY in the form of secured advances that bear interest at a floating rate. As of December 31, 2019 , we had a total of $39.5 million in outstanding secured advances with an average spread of 25 basis points over 30 -day LIBOR. Master Repurchase Agreement The Company entered into a Master Repurchase Agreement, or MRA, known as the 2017 MRA, which provides us with the ability to sell certain mortgage 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 facility 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. The 2017 MRA has 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. In June 2018, we exercised a one year extension option and in June 2019, we exercised another one year extension option. In August 2019, we amended our agreement to include two additional one year extension options. At December 31, 2019 , the facility had a carrying value of $152.4 million, net of deferred financing costs. 2017 Credit Facility In November 2017, we entered into an amendment to the credit facility, referred to as the 2017 credit facility, that was originally entered into by the Company in November 2012, or the 2012 credit facility. As of December 31, 2019 , the 2017 credit facility consisted of a $1.5 billion revolving credit facility, a $1.3 billion term loan (or "Term Loan A"), and a $200.0 million term loan (or "Term Loan B") with maturity dates of March 31, 2022, March 31, 2023, and November 21, 2024, respectively. The revolving credit facility has two six -month as-of-right extension options to March 31, 2023. We also have an option, subject to customary conditions, to increase the capacity of the credit facility to $4.5 billion at any time prior to the maturity dates for the revolving credit facility and term loans without the consent of existing lenders, by obtaining additional commitments from our existing lenders and other financial institutions. As of December 31, 2019 , 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) 85 basis points to 165 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. In May 2019, we entered into an agreement to reduce the interest rate spread under Term Loan B by 65 basis points to a spread over 30 -day LIBOR ranging from 85 basis points to 165 basis points. This reduction was effective in November 2019. At December 31, 2019 , the applicable spread was 100 basis points for the revolving credit facility, 110 basis points for Term Loan A, and 100 basis points for Term Loan B. We are required to pay quarterly in arrears a 12.5 to 30 basis point facility fee on the total commitments under the revolving credit facility based on the credit rating assigned to the senior unsecured long term indebtedness of the Company. As of December 31, 2019 , the facility fee was 20 basis points. As of December 31, 2019 , we had $11.8 million of outstanding letters of credit, $240.0 million drawn under the revolving credit facility and $1.5 billion outstanding under the term loan facilities, with total undrawn capacity of $1.3 billion under the 2017 credit facility. At December 31, 2019 and December 31, 2018 , the revolving credit facility had a carrying value of $234.0 million and $492.2 million , respectively, net of deferred financing costs. At December 31, 2019 and December 31, 2018 , the term loan facilities had a carrying value of $1.5 billion and $1.5 billion , respectively, net of deferred financing costs. The Company and the Operating Partnership are borrowers jointly and severally obligated under the 2017 credit facility. The 2017 credit facility includes certain restrictions and covenants (see Restrictive Covenants below). Senior Unsecured Notes The following table sets forth our senior unsecured notes and other related disclosures as of December 31, 2019 and 2018 , respectively, by scheduled maturity date (dollars in thousands): Issuance December 31, 2019 Unpaid Principal Balance December 31, 2019 Accreted Balance December 31, 2018 Accreted Balance Interest Rate (1) Initial Term (in Years) Maturity Date March 16, 2010 (2) $ 250,000 $ 250,000 $ 250,000 7.75 % 10 March 2020 August 7, 2018 (3) (4) 350,000 350,000 350,000 L+ 0.98 % 3 August 2021 October 5, 2017 (3) 500,000 499,695 499,591 3.25 % 5 October 2022 November 15, 2012 (5) 300,000 303,142 304,168 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 $ 1,500,000 $ 1,502,837 $ 1,503,759 Deferred financing costs, net (5,990 ) (8,545 ) $ 1,500,000 $ 1,496,847 $ 1,495,214 (1) Interest rate as of December 31, 2019 , taking into account interest rate hedges in effect during the period. Floating rate notes are presented with the stated spread over 3-month LIBOR, unless otherwise specified. (2) Issued by the Company and the Operating Partnership as co-obligors. (3) Issued by the Operating Partnership with the Company as the guarantor. (4) Beginning on August 8, 2019 and at any time thereafter, the notes are subject to redemption at the Company's option, in whole but not in part, at a redemption price equal to 100% of the principal amount of the notes, plus unpaid accrued interest thereon to the redemption date. (5) In October 2017, the Company and the Operating Partnership as co-obligors issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022. The notes were priced at 105.334% of par. Restrictive Covenants The terms of the 2017 credit facility and certain of our senior unsecured notes include certain restrictions and covenants which may limit, among other things, our ability to pay dividends, make certain types of investments, incur additional indebtedness, incur liens and enter into negative pledge agreements and dispose of assets, and which require compliance with financial ratios relating to the maximum ratio of total indebtedness to total asset value, a minimum ratio of EBITDA to fixed charges, a maximum ratio of secured indebtedness to total asset value and a maximum ratio of unsecured indebtedness to unencumbered asset value. The dividend restriction referred to above provides that, we will not during any time when a default is continuing, make distributions with respect to common stock or other equity interests, except to enable the Company to continue to qualify as a REIT for Federal income tax purposes. As of December 31, 2019 and 2018 , we were in compliance with all such covenants. Junior Subordinated Deferrable Interest Debentures In June 2005, the Company and the Operating Partnership issued $100.0 million in unsecured trust preferred securities through a newly formed trust, SL Green Capital Trust I, or the Trust, which is a wholly-owned subsidiary of the Operating Partnership. The securities mature in 2035 and bear interest at a floating rate of 125 basis points over the three-month LIBOR. Interest payments may be deferred for a period of up to eight consecutive quarters if the Operating Partnership exercises its right to defer such payments. The Trust preferred securities are redeemable at the option of the Operating Partnership, in whole or in part, with no prepayment premium. We do not consolidate the Trust even though it is a variable interest entity as we are not the primary beneficiary. Because the Trust is not consolidated, we have recorded the debt on our consolidated balance sheets and the related payments are classified as interest expense. Principal Maturities Combined aggregate principal maturities of mortgages and other loans payable, 2017 credit facility, trust preferred securities, senior unsecured notes and our share of joint venture debt as of December 31, 2019 , including as-of-right extension options and put options, were as follows (dollars in thousands): Scheduled Amortization Principal Revolving Credit Facility Unsecured Term Loans Trust Preferred Securities Senior Unsecured Notes Total Joint Venture Debt 2020 $ 11,118 $ 207,706 $ — $ — $ — $ 250,000 $ 468,824 $ 811,628 2021 11,638 239,908 — — — 350,000 601,546 805,276 2022 9,430 529,375 — — — 800,000 1,338,805 268,952 2023 7,301 50,000 240,000 1,300,000 — — 1,597,301 311,436 2024 6,032 272,749 — 200,000 — — 478,781 17,022 Thereafter 3,258 863,368 — — 100,000 100,000 1,066,626 1,813,821 $ 48,777 $ 2,163,106 $ 240,000 $ 1,500,000 $ 100,000 $ 1,500,000 $ 5,551,883 $ 4,028,135 Consolidated interest expense, excluding capitalized interest, was comprised of the following (dollars in thousands): Year Ended December 31, 2019 2018 2017 Interest expense before capitalized interest $ 246,848 $ 236,719 $ 281,551 Interest on financing leases 3,243 8,069 3,098 Interest capitalized (55,446 ) (34,162 ) (26,020 ) Interest income (4,124 ) (1,957 ) (1,584 ) Interest expense, net $ 190,521 $ 208,669 $ 257,045

Corporate Indebtedness

Corporate Indebtedness	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Corporate Indebtedness	Mortgages and Other Loans Payable The first mortgages and other loans payable collateralized by the respective properties and assignment of leases or debt investments at December 31, 2019 and 2018 , respectively, were as follows (dollars in thousands): Property Maturity Date Interest Rate (1) December 31, 2019 December 31, 2018 Fixed Rate Debt: 762 Madison Avenue February 2022 5.00% $ 771 $ 771 100 Church Street July 2022 4.68% 209,296 213,208 420 Lexington Avenue October 2024 3.99% 299,165 300,000 400 East 58th Street (2) November 2026 3.00% 39,094 39,931 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 3.59% 35,123 35,807 315 West 33rd Street February 2027 4.17% 250,000 250,000 Total fixed rate debt $ 1,383,449 $ 1,389,717 Floating Rate Debt: FHLB Facility (4) January 2020 L+ 0.26% $ 10,000 $ — FHLB Facility (5) February 2020 L+ 0.32% 15,000 — FHLB Facility June 2020 L+ 0.17% 14,500 — 2017 Master Repurchase Agreement June 2020 L+ 2.19% 152,684 300,000 133 Greene Street August 2020 L+ 2.00% 15,523 15,523 106 Spring Street January 2021 L+ 2.50% 38,025 — 609 Fifth Avenue March 2021 L+ 2.40% 53,773 — 185 Broadway (6) November 2021 L+ 2.85% 120,110 111,869 712 Madison Avenue December 2021 L+ 1.85% 28,000 28,000 410 Tenth Avenue (7) May 2022 L+ 2.23% 330,819 — 719 Seventh Avenue September 2023 L+ 1.20% 50,000 50,000 FHLB Facility (8) — 13,000 115 Spring Street (9) — 65,550 FHLB Facility (10) — 14,500 Total floating rate debt $ 828,434 $ 598,442 Total mortgages and other loans payable $ 2,211,883 $ 1,988,159 Deferred financing costs, net of amortization (28,630 ) (26,919 ) Total mortgages and other loans payable, net $ 2,183,253 $ 1,961,240 (1) Interest rate as of December 31, 2019 , 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 $34.2 million mortgage loan and $0.9 million mezzanine 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) In January 2020, the loan was repaid and a new advance was drawn in the amount of $10.0 million with a spread of 16.5 basis points. (5) In February 2020, the loan was repaid and a new advance was drawn in the amount of $15.0 million with a spread of 26.0 basis points. (6) This loan is a $225.0 million construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial three year term with two one year extension options. Advances under the loan are subject to incurred costs and funded equity requirements. (7) This loan is a $465.0 million construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial three year term with two one year extension options. Advances under the loan are subject to incurred costs and funded equity requirements. (8) In August 2019, the loan was repaid. (9) In August 2019, the Company sold a 49% interest in the property to a private investor. The transaction resulted in the deconsolidation of our remaining 51% interest. See Note 6, "Investments in Unconsolidated Joint Ventures." (10) In December 2019, the loan was repaid. At December 31, 2019 and 2018 , the gross book value of the properties and debt and preferred equity investments collateralizing the mortgages and other loans payable was approximately $3.3 billion and $2.6 billion, respectively. Federal Home Loan Bank of New York ("FHLB") Facility The Company’s wholly-owned subsidiary, Ticonderoga Insurance Company, or Ticonderoga, a Vermont licensed captive insurance company, is a member of the Federal Home Loan Bank of New York, or FHLBNY. As a member, Ticonderoga may borrow funds from the FHLBNY in the form of secured advances that bear interest at a floating rate. As of December 31, 2019 , we had a total of $39.5 million in outstanding secured advances with an average spread of 25 basis points over 30 -day LIBOR. Master Repurchase Agreement The Company entered into a Master Repurchase Agreement, or MRA, known as the 2017 MRA, which provides us with the ability to sell certain mortgage 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 facility 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. The 2017 MRA has 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. In June 2018, we exercised a one year extension option and in June 2019, we exercised another one year extension option. In August 2019, we amended our agreement to include two additional one year extension options. At December 31, 2019 , the facility had a carrying value of $152.4 million, net of deferred financing costs. 2017 Credit Facility In November 2017, we entered into an amendment to the credit facility, referred to as the 2017 credit facility, that was originally entered into by the Company in November 2012, or the 2012 credit facility. As of December 31, 2019 , the 2017 credit facility consisted of a $1.5 billion revolving credit facility, a $1.3 billion term loan (or "Term Loan A"), and a $200.0 million term loan (or "Term Loan B") with maturity dates of March 31, 2022, March 31, 2023, and November 21, 2024, respectively. The revolving credit facility has two six -month as-of-right extension options to March 31, 2023. We also have an option, subject to customary conditions, to increase the capacity of the credit facility to $4.5 billion at any time prior to the maturity dates for the revolving credit facility and term loans without the consent of existing lenders, by obtaining additional commitments from our existing lenders and other financial institutions. As of December 31, 2019 , 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) 85 basis points to 165 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. In May 2019, we entered into an agreement to reduce the interest rate spread under Term Loan B by 65 basis points to a spread over 30 -day LIBOR ranging from 85 basis points to 165 basis points. This reduction was effective in November 2019. At December 31, 2019 , the applicable spread was 100 basis points for the revolving credit facility, 110 basis points for Term Loan A, and 100 basis points for Term Loan B. We are required to pay quarterly in arrears a 12.5 to 30 basis point facility fee on the total commitments under the revolving credit facility based on the credit rating assigned to the senior unsecured long term indebtedness of the Company. As of December 31, 2019 , the facility fee was 20 basis points. As of December 31, 2019 , we had $11.8 million of outstanding letters of credit, $240.0 million drawn under the revolving credit facility and $1.5 billion outstanding under the term loan facilities, with total undrawn capacity of $1.3 billion under the 2017 credit facility. At December 31, 2019 and December 31, 2018 , the revolving credit facility had a carrying value of $234.0 million and $492.2 million , respectively, net of deferred financing costs. At December 31, 2019 and December 31, 2018 , the term loan facilities had a carrying value of $1.5 billion and $1.5 billion , respectively, net of deferred financing costs. The Company and the Operating Partnership are borrowers jointly and severally obligated under the 2017 credit facility. The 2017 credit facility includes certain restrictions and covenants (see Restrictive Covenants below). Senior Unsecured Notes The following table sets forth our senior unsecured notes and other related disclosures as of December 31, 2019 and 2018 , respectively, by scheduled maturity date (dollars in thousands): Issuance December 31, 2019 Unpaid Principal Balance December 31, 2019 Accreted Balance December 31, 2018 Accreted Balance Interest Rate (1) Initial Term (in Years) Maturity Date March 16, 2010 (2) $ 250,000 $ 250,000 $ 250,000 7.75 % 10 March 2020 August 7, 2018 (3) (4) 350,000 350,000 350,000 L+ 0.98 % 3 August 2021 October 5, 2017 (3) 500,000 499,695 499,591 3.25 % 5 October 2022 November 15, 2012 (5) 300,000 303,142 304,168 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 $ 1,500,000 $ 1,502,837 $ 1,503,759 Deferred financing costs, net (5,990 ) (8,545 ) $ 1,500,000 $ 1,496,847 $ 1,495,214 (1) Interest rate as of December 31, 2019 , taking into account interest rate hedges in effect during the period. Floating rate notes are presented with the stated spread over 3-month LIBOR, unless otherwise specified. (2) Issued by the Company and the Operating Partnership as co-obligors. (3) Issued by the Operating Partnership with the Company as the guarantor. (4) Beginning on August 8, 2019 and at any time thereafter, the notes are subject to redemption at the Company's option, in whole but not in part, at a redemption price equal to 100% of the principal amount of the notes, plus unpaid accrued interest thereon to the redemption date. (5) In October 2017, the Company and the Operating Partnership as co-obligors issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022. The notes were priced at 105.334% of par. Restrictive Covenants The terms of the 2017 credit facility and certain of our senior unsecured notes include certain restrictions and covenants which may limit, among other things, our ability to pay dividends, make certain types of investments, incur additional indebtedness, incur liens and enter into negative pledge agreements and dispose of assets, and which require compliance with financial ratios relating to the maximum ratio of total indebtedness to total asset value, a minimum ratio of EBITDA to fixed charges, a maximum ratio of secured indebtedness to total asset value and a maximum ratio of unsecured indebtedness to unencumbered asset value. The dividend restriction referred to above provides that, we will not during any time when a default is continuing, make distributions with respect to common stock or other equity interests, except to enable the Company to continue to qualify as a REIT for Federal income tax purposes. As of December 31, 2019 and 2018 , we were in compliance with all such covenants. Junior Subordinated Deferrable Interest Debentures In June 2005, the Company and the Operating Partnership issued $100.0 million in unsecured trust preferred securities through a newly formed trust, SL Green Capital Trust I, or the Trust, which is a wholly-owned subsidiary of the Operating Partnership. The securities mature in 2035 and bear interest at a floating rate of 125 basis points over the three-month LIBOR. Interest payments may be deferred for a period of up to eight consecutive quarters if the Operating Partnership exercises its right to defer such payments. The Trust preferred securities are redeemable at the option of the Operating Partnership, in whole or in part, with no prepayment premium. We do not consolidate the Trust even though it is a variable interest entity as we are not the primary beneficiary. Because the Trust is not consolidated, we have recorded the debt on our consolidated balance sheets and the related payments are classified as interest expense. Principal Maturities Combined aggregate principal maturities of mortgages and other loans payable, 2017 credit facility, trust preferred securities, senior unsecured notes and our share of joint venture debt as of December 31, 2019 , including as-of-right extension options and put options, were as follows (dollars in thousands): Scheduled Amortization Principal Revolving Credit Facility Unsecured Term Loans Trust Preferred Securities Senior Unsecured Notes Total Joint Venture Debt 2020 $ 11,118 $ 207,706 $ — $ — $ — $ 250,000 $ 468,824 $ 811,628 2021 11,638 239,908 — — — 350,000 601,546 805,276 2022 9,430 529,375 — — — 800,000 1,338,805 268,952 2023 7,301 50,000 240,000 1,300,000 — — 1,597,301 311,436 2024 6,032 272,749 — 200,000 — — 478,781 17,022 Thereafter 3,258 863,368 — — 100,000 100,000 1,066,626 1,813,821 $ 48,777 $ 2,163,106 $ 240,000 $ 1,500,000 $ 100,000 $ 1,500,000 $ 5,551,883 $ 4,028,135 Consolidated interest expense, excluding capitalized interest, was comprised of the following (dollars in thousands): Year Ended December 31, 2019 2018 2017 Interest expense before capitalized interest $ 246,848 $ 236,719 $ 281,551 Interest on financing leases 3,243 8,069 3,098 Interest capitalized (55,446 ) (34,162 ) (26,020 ) Interest income (4,124 ) (1,957 ) (1,584 ) Interest expense, net $ 190,521 $ 208,669 $ 257,045

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Cleaning/ Security/ Messenger and Restoration Services Alliance Building Services, or Alliance, and its affiliates are partially owned by Gary Green, a son of Stephen L. Green, who serves as a member and as the chairman emeritus of our board of directors, and provide services to certain properties owned by us. Alliance’s affiliates include First Quality Maintenance, L.P., or First Quality, Classic Security LLC, Bright Star Couriers LLC and Onyx Restoration Works, and provide cleaning, extermination, security, messenger, and restoration services, respectively. In addition, First Quality has the non-exclusive opportunity to provide cleaning and related services to individual tenants at our properties on a basis separately negotiated with any tenant seeking such additional services. The Service Corporation has entered into an arrangement with Alliance whereby it will receive a profit participation above a certain threshold for services provided by Alliance to certain tenants at certain buildings above the base services specified in their lease agreements. Income earned from the profit participation, which is included in other income on the consolidated statements of operations, was $3.9 million , $3.9 million and $3.9 million for the years ended December 31, 2019 , 2018 and 2017 , respectively. We also recorded expenses, inclusive of capitalized expenses, of $18.8 million , $18.8 million and $22.6 million for the years ended December 31, 2019 , 2018 and 2017 , respectively, for these services (excluding services provided directly to tenants). Management Fees S.L. Green Management Corp., a consolidated entity, receives property management fees from an entity in which Stephen L. Green owns an interest. We received management fees from this entity of $0.6 million , $0.6 million and $0.5 million for the years ended December 31, 2019 , 2018 , and 2017 respectively. One Vanderbilt Investment In December 2016, we entered into agreements with entities owned and controlled by our Chairman and CEO, Marc Holliday, and our President, Andrew Mathias, pursuant to which they agreed to make an investment in our One Vanderbilt project at the appraised fair market value for the interests acquired. This investment entitles these entities to receive approximately 1.50 % - 1.80 % and 1.00 % - 1.20 %, respectively, of any profits realized by the Company from its One Vanderbilt project in excess of the Company’s capital contributions. The entities have no right to any return of capital. Accordingly, subject to previously disclosed repurchase rights, these interests will have no value and will not entitle these entities to any amounts (other than limited distributions to cover tax liabilities incurred) unless and until the Company has received distributions from the One Vanderbilt project in excess of the Company’s aggregate investment in the project. In the event that the Company does not realize a profit on its investment in the project (or would not realize a profit based on the value at the time the interests are repurchased), the entities owned and controlled by Messrs. Holliday and Mathias will lose the entire amount of their investment. The entities owned and controlled by Messrs. Holliday and Mathias paid $1.4 million and $1.0 million , respectively, which equal the fair market value of the interests acquired as of the date the investment agreements were entered into as determined by an independent third party appraisal that we obtained. Messrs. Holliday and Mathias cannot monetize their interests until after stabilization of the property ( 50 % within three years after stabilization and 100 % three years or more after stabilization). In addition, the agreement calls for us to repurchase these interests in the event of a sale of One Vanderbilt or a transactional change of control of the Company. We also have the right to repurchase these interests on the seven -year anniversary of the stabilization of the project or upon the occurrence of certain separation events prior to the stabilization of the project relating to each of Messrs. Holliday’s and Mathias’s continued service with us. The price paid upon monetization of the interests will equal the liquidation value of the interests at the time, with the value of One Vanderbilt being based on its sale price, if applicable, or fair market value as determined by an independent third party appraiser. Other We are entitled to receive fees for providing management, leasing, construction supervision, and asset management services to certain of our joint ventures as further described in Note 6, "Investments in Unconsolidated Joint Ventures." Amounts due from joint ventures and related parties at December 31, 2019 and 2018 consisted of the following (in thousands): December 31, 2019 2018 Due from joint ventures $ 9,352 $ 18,655 Other 11,769 9,378 Related party receivables $ 21,121 $ 28,033

Noncontrolling Interests on the

Noncontrolling Interests on the Company's Consolidated Financial Statements	12 Months Ended
	Dec. 31, 2019
Noncontrolling Interest [Abstract]
Noncontrolling Interests on the Company's Consolidated Financial Statements	Noncontrolling Interests on the Company's Consolidated Financial Statements Noncontrolling interests represent the common and preferred units of limited partnership interest in the Operating Partnership not held by the Company as well as third party equity interests in our other consolidated subsidiaries. Noncontrolling interests in the Operating Partnership are shown in the mezzanine equity while the noncontrolling interests in our other consolidated subsidiaries are shown in the equity section of the Company’s consolidated financial statements. Common Units of Limited Partnership Interest in the Operating Partnership As of December 31, 2019 and 2018 , the noncontrolling interest unit holders owned 5.03% , or 4,195,875 units, and 4.70% , or 4,130,579 units, of the Operating Partnership, respectively. As of December 31, 2019 , 4,195,875 shares of our common stock were reserved for issuance upon the redemption of units of limited partnership interest of the Operating Partnership. Noncontrolling interests in the Operating Partnership is recorded at the greater of its cost basis or fair market value based on the closing stock price of our common stock at the end of the reporting period. Below is a summary of the activity relating to the noncontrolling interests in the Operating Partnership as of December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Balance at beginning of period $ 387,805 $ 461,954 Distributions (14,729 ) (15,000 ) Issuance of common units 19,403 23,655 Redemption of common units (27,962 ) (60,718 ) Net income 13,301 12,216 Accumulated other comprehensive income allocation (2,276 ) (66 ) Fair value adjustment 34,320 (34,236 ) Balance at end of period $ 409,862 $ 387,805 Preferred Units of Limited Partnership Interest in the Operating Partnership Below is a summary of the preferred units of limited partnership interest in the Operating Partnership as of December 31, 2019 : Issuance Number of Units Authorized Number of Units Issued Dividends Per Unit (1) Liquidation Preference Per Unit (2) Conversion Price Per Unit (3) Date of Issuance 4.50% Series G (4) 1,902,000 1,902,000 $ 1.1250 $ 25.00 $ 88.50 January 2012 7.00% Series F 60 60 $ 70.0000 $ 1,000.00 $ 29.12 January 2007 3.50% Series K 700,000 563,954 $ 0.8750 $ 25.00 $ 134.67 August 2014 4.00% Series L 500,000 378,634 $ 1.0000 $ 25.00 — August 2014 3.75% Series M 1,600,000 1,600,000 $ 0.9375 $ 25.00 — February 2015 3.00% Series N (5) 552,303 552,303 $ 0.7500 $ 25.00 — June 2015 Series O (6) 1 1 (6 ) (6 ) — June 2015 4.00% Series P 200,000 200,000 $ 1.0000 $ 25.00 — July 2015 3.50% Series Q 268,000 268,000 $ 0.8750 $ 25.00 $ 148.95 July 2015 3.50% Series R 400,000 400,000 $ 0.8750 $ 25.00 $ 154.89 August 2015 4.00% Series S 1,077,280 1,077,280 $ 1.0000 $ 25.00 — August 2015 2.75% Series T 230,000 230,000 $ 0.6875 $ 25.00 $ 119.02 March 2016 4.50% Series U (7) 680,000 680,000 $ 1.1250 $ 25.00 — March 2016 3.50% Series A (8) 109,161 109,161 $ 35.0000 $ 1,000.00 — August 2015 3.50% Series V 40,000 40,000 $ 0.8750 $ 25.00 — May 2019 (1) Dividends are cumulative, subject to certain provisions. (2) Units are redeemable at any time at par for cash at the option of the unitholder unless otherwise specified. (3) If applicable, 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) the amount shown in the table. (4) Common units of limited partnership interest in the Operating Partnership issued in a conversion 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. (5) All of the outstanding units were redeemed at par for cash by the unitholder during the twelve months ended December 31, 2019 . (6) The holder of the Series O preferred unit is entitled to quarterly dividends in an amount calculated as (i) 1,350 multiplied by (ii) the current distribution per common unit of limited partnership in SL Green Operating Partnership. The holder has the right to require the Operating Partnership to repurchase the Series O unit for cash at a price that is determined based on the closing price of the Company's common stock at the time such right is exercised. The unit's liquidation preference is the fair market value of the unit at the time of a liquidation event. (7) The annual dividend is subject to reduction upon the occurrence of certain circumstances. The minimum annual dividend is $0.75 per unit. (8) Issued through a consolidated subsidiary. The units are convertible on a one-for-one basis, into the Series B Preferred Units of limited partnership interest, or the Subsidiary Series B Preferred Units. The Subsidiary Series B Preferred Units can be converted at any time, at the option of the unitholder, into a number of common stock equal to 6.71348 shares of common stock for each Subsidiary Series B Preferred Unit. As of December 31, 2019 , no Subsidiary Series B Preferred Units have been issued. Below is a summary of the activity relating to the preferred units in the Operating Partnership as of December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Balance at beginning of period $ 300,427 $ 301,735 Issuance of preferred units 1,000 — Redemption of preferred units (18,142 ) (1,308 ) Balance at end of period $ 283,285 $ 300,427

Stockholders' Equity of the Com

Stockholders' Equity of the Company	12 Months Ended
	Dec. 31, 2019
Stockholders' Equity Note [Abstract]
Stockholders' Equity of the Company	Stockholders’ Equity of the Company Common Stock Our authorized capital stock consists of 260,000,000 shares, $0.01 par value per share, consisting of 160,000,000 shares of common stock, $0.01 par value per share, 75,000,000 shares of excess stock, at $0.01 par value per share, and 25,000,000 shares of preferred stock, par value $0.01 per share. As of December 31, 2019 , 79,202,322 shares of common stock and no shares of excess stock were issued and outstanding. Share Repurchase Program In August 2016, our Board of Directors approved a share repurchase program under which we can buy up to $1.0 billion of shares of our common stock. The Board of Directors has since authorized four separate $500.0 million increases to the size of the share repurchase program in the fourth quarter of 2017, second quarter of 2018, fourth quarter of 2018, and fourth quarter of 2019 bringing the total program size to $3.0 billion . At December 31, 2019 repurchases executed under the program were as follows: Period Shares repurchased Average price paid per share Cumulative number of shares repurchased as part of the repurchase plan or programs Year ended 2017 8,342,411 $101.64 8,342,411 Year ended 2018 9,744,911 $96.22 18,087,322 Year ended 2019 4,596,171 $83.62 22,683,493 At-The-Market Equity Offering Program In March 2015, the Company, along with the Operating Partnership, entered into an "at-the-market" equity offering program, or ATM Program, to sell an aggregate of $300.0 million of our common stock. The Company did not make any sales of its common stock under the ATM program in the years ended December 31, 2019 , 2018 , or 2017 . Perpetual Preferred Stock We have 9,200,000 shares of our 6.50% Series I Cumulative Redeemable Preferred Stock, or the Series I Preferred Stock, outstanding with a mandatory liquidation preference of $25.00 per share. The Series I Preferred stockholders receive annual dividends of $1.625 per share paid on a quarterly basis and dividends are cumulative, subject to certain provisions. We are entitled to redeem the Series I Preferred Stock at par for cash at our option. In August 2012, we received $221.9 million in net proceeds from the issuance of the Series I Preferred Stock, which were recorded net of underwriters' discount and issuance costs, and contributed the net proceeds to the Operating Partnership in exchange for 9,200,000 units of 6.50% Series I Cumulative Redeemable Preferred Units of limited partnership interest, or the Series I Preferred Units. Dividend Reinvestment and Stock Purchase Plan ("DRSPP") In February 2018, the Company filed a registration statement with the SEC for our dividend reinvestment and stock purchase plan, or DRSPP, which automatically became effective upon filing. The Company registered 3,500,000 shares of our common stock under the DRSPP. The DRSPP commenced on September 24, 2001. The following table summarizes SL Green common stock issued, and proceeds received from dividend reinvestments and/or stock purchases under the DRSPP for the years ended December 31, 2019 , 2018 , and 2017 , respectively (dollars in thousands): Year Ended December 31, 2019 2018 2017 Shares of common stock issued 3,867 1,399 2,141 Dividend reinvestments/stock purchases under the DRSPP $ 334 $ 136 $ 223 Earnings per Share We use the two-class method of computing earnings per share (“EPS”), which is an earnings allocation formula that determines EPS for common stock and any participating securities according to dividends declared (whether paid or unpaid). Under the two-class method, basic EPS is computed by dividing the income available to common stockholders by the weighted-average number of common stock shares outstanding for the period. Diluted EPS reflects the potential dilution that could occur from share equivalent activity. SL Green's earnings per share for the years ended December 31, 2019 , 2018 , and 2017 are computed as follows (in thousands): Year Ended December 31, Numerator 2019 2018 2017 Basic Earnings: Income attributable to SL Green common stockholders $ 255,484 $ 232,312 $ 86,424 Less: distributed earnings allocated to participating securities (1,739 ) $ (552 ) $ (471 ) Net income attributable to SL Green common stockholders (numerator for basic earnings per share) $ 253,745 $ 231,760 $ 85,953 Add back: Dilutive effect of earnings allocated to participating securities 1,719 552 471 Add back: Effect of dilutive securities (redemption of units to common shares) 13,301 12,216 3,995 Income attributable to SL Green common stockholders (numerator for diluted earnings per share) $ 268,765 $ 244,528 $ 90,419 Year Ended December 31, Denominator 2019 2018 2017 Basic Shares: Weighted average common stock outstanding 81,733 86,753 98,571 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,275 4,562 4,556 Stock-based compensation plans 554 215 276 Diluted weighted average common stock outstanding 86,562 91,530 103,403 SL Green has excluded 1,252,670 , 1,138,647 and 774,782 common stock equivalents from the diluted shares outstanding for the years ended December 31, 2019 , 2018 , and 2017

Partners' Capital of the Operat

Partners' Capital of the Operating Partnership	12 Months Ended
	Dec. 31, 2019
Stockholders' Equity
Partners' Capital of the Operating Partnership	Stockholders’ Equity of the Company Common Stock Our authorized capital stock consists of 260,000,000 shares, $0.01 par value per share, consisting of 160,000,000 shares of common stock, $0.01 par value per share, 75,000,000 shares of excess stock, at $0.01 par value per share, and 25,000,000 shares of preferred stock, par value $0.01 per share. As of December 31, 2019 , 79,202,322 shares of common stock and no shares of excess stock were issued and outstanding. Share Repurchase Program In August 2016, our Board of Directors approved a share repurchase program under which we can buy up to $1.0 billion of shares of our common stock. The Board of Directors has since authorized four separate $500.0 million increases to the size of the share repurchase program in the fourth quarter of 2017, second quarter of 2018, fourth quarter of 2018, and fourth quarter of 2019 bringing the total program size to $3.0 billion . At December 31, 2019 repurchases executed under the program were as follows: Period Shares repurchased Average price paid per share Cumulative number of shares repurchased as part of the repurchase plan or programs Year ended 2017 8,342,411 $101.64 8,342,411 Year ended 2018 9,744,911 $96.22 18,087,322 Year ended 2019 4,596,171 $83.62 22,683,493 At-The-Market Equity Offering Program In March 2015, the Company, along with the Operating Partnership, entered into an "at-the-market" equity offering program, or ATM Program, to sell an aggregate of $300.0 million of our common stock. The Company did not make any sales of its common stock under the ATM program in the years ended December 31, 2019 , 2018 , or 2017 . Perpetual Preferred Stock We have 9,200,000 shares of our 6.50% Series I Cumulative Redeemable Preferred Stock, or the Series I Preferred Stock, outstanding with a mandatory liquidation preference of $25.00 per share. The Series I Preferred stockholders receive annual dividends of $1.625 per share paid on a quarterly basis and dividends are cumulative, subject to certain provisions. We are entitled to redeem the Series I Preferred Stock at par for cash at our option. In August 2012, we received $221.9 million in net proceeds from the issuance of the Series I Preferred Stock, which were recorded net of underwriters' discount and issuance costs, and contributed the net proceeds to the Operating Partnership in exchange for 9,200,000 units of 6.50% Series I Cumulative Redeemable Preferred Units of limited partnership interest, or the Series I Preferred Units. Dividend Reinvestment and Stock Purchase Plan ("DRSPP") In February 2018, the Company filed a registration statement with the SEC for our dividend reinvestment and stock purchase plan, or DRSPP, which automatically became effective upon filing. The Company registered 3,500,000 shares of our common stock under the DRSPP. The DRSPP commenced on September 24, 2001. The following table summarizes SL Green common stock issued, and proceeds received from dividend reinvestments and/or stock purchases under the DRSPP for the years ended December 31, 2019 , 2018 , and 2017 , respectively (dollars in thousands): Year Ended December 31, 2019 2018 2017 Shares of common stock issued 3,867 1,399 2,141 Dividend reinvestments/stock purchases under the DRSPP $ 334 $ 136 $ 223 Earnings per Share We use the two-class method of computing earnings per share (“EPS”), which is an earnings allocation formula that determines EPS for common stock and any participating securities according to dividends declared (whether paid or unpaid). Under the two-class method, basic EPS is computed by dividing the income available to common stockholders by the weighted-average number of common stock shares outstanding for the period. Diluted EPS reflects the potential dilution that could occur from share equivalent activity. SL Green's earnings per share for the years ended December 31, 2019 , 2018 , and 2017 are computed as follows (in thousands): Year Ended December 31, Numerator 2019 2018 2017 Basic Earnings: Income attributable to SL Green common stockholders $ 255,484 $ 232,312 $ 86,424 Less: distributed earnings allocated to participating securities (1,739 ) $ (552 ) $ (471 ) Net income attributable to SL Green common stockholders (numerator for basic earnings per share) $ 253,745 $ 231,760 $ 85,953 Add back: Dilutive effect of earnings allocated to participating securities 1,719 552 471 Add back: Effect of dilutive securities (redemption of units to common shares) 13,301 12,216 3,995 Income attributable to SL Green common stockholders (numerator for diluted earnings per share) $ 268,765 $ 244,528 $ 90,419 Year Ended December 31, Denominator 2019 2018 2017 Basic Shares: Weighted average common stock outstanding 81,733 86,753 98,571 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,275 4,562 4,556 Stock-based compensation plans 554 215 276 Diluted weighted average common stock outstanding 86,562 91,530 103,403 SL Green has excluded 1,252,670 , 1,138,647 and 774,782 common stock equivalents from the diluted shares outstanding for the years ended December 31, 2019 , 2018 , and 2017
SL Green Operating Partnership
Stockholders' Equity
Partners' Capital of the Operating Partnership	Partners' Capital of the Operating Partnership The Company is the sole managing general partner of the Operating Partnership and at December 31, 2019 owned 79,202,322 general and limited partnership interests in the Operating Partnership and 9,200,000 Series I Preferred Units. Partnership interests in the Operating Partnership are denominated as “common units of limited partnership interest” (also referred to as “OP Units”) or “preferred units of limited partnership interest” (also referred to as “Preferred Units”). All references to OP Units and Preferred Units outstanding exclude such units held by the Company. A holder of an OP Unit may present such OP Unit to the Operating Partnership for redemption at any time (subject to restrictions agreed upon at the issuance of OP Units to particular holders that may restrict such right for a period of time, generally one year from issuance). Upon presentation of an OP Unit for redemption, the Operating Partnership must redeem such OP Unit in exchange for the cash equal to the then value of a share of common stock of the Company, except that the Company may, at its election, in lieu of cash redemption, acquire such OP Unit for one share of common stock. Because the number of shares of common stock outstanding at all times equals the number of OP Units that the Company owns, one share of common stock is generally the economic equivalent of one OP Unit, and the quarterly distribution that may be paid to the holder of an OP Unit equals the quarterly dividend that may be paid to the holder of a share of common stock. Each series of Preferred Units makes a distribution that is set in accordance with an amendment to the partnership agreement of the Operating Partnership. Preferred Units may also be convertible into OP Units at the election of the holder thereof or the Company, subject to the terms of such Preferred Units. Net income (loss) allocated to the preferred unitholders and common unitholders reflects their pro rata share of net income (loss) and distributions. Limited Partner Units As of December 31, 2019 , limited partners other than SL Green owned 5.03% , or 4,195,875 common units, of the Operating Partnership. Preferred Units Preferred units not owned by SL Green are further described in Note 11, “Noncontrolling Interests on the Company’s Consolidated Financial Statements - Preferred Units of Limited Partnership Interest in the Operating Partnership.” Earnings per Unit The Operating Partnership's earnings per unit for the years ended December 31, 2019 , 2018 , and 2017 respectively are computed as follows (in thousands): Year Ended December 31, Numerator 2019 2018 2017 Basic Earnings: Income attributable to SLGOP common unitholders $ 268,785 $ 244,528 $ 90,419 Less: distributed earnings allocated to participating securities (1,739 ) $ (552 ) $ (471 ) Net Income attributable to SLGOP common unitholders (numerator for basic earnings per unit) $ 267,046 $ 243,976 $ 89,948 Add back: Dilutive effect of earnings allocated to participating securities 1,719 552 471 Income attributable to SLGOP common unitholders $ 268,765 $ 244,528 $ 90,419 Year Ended December 31, Denominator 2019 2018 2017 Basic units: Weighted average common units outstanding 86,008 91,315 103,127 Effect of Dilutive Securities: Stock-based compensation plans 554 215 276 Diluted weighted average common units outstanding 86,562 91,530 103,403 The Operating Partnership has excluded 1,252,670 , 1,138,647 , and 774,782 common unit equivalents from the diluted units outstanding for the years ended December 31, 2019 , 2018 , and 2017

Share-based Compensation

Share-based Compensation	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [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. The Fourth Amended and Restated 2005 Stock Option and Incentive Plan, or the 2005 Plan, was approved by the Company's board of directors in April 2016 and its stockholders in June 2016 at the Company's annual meeting of stockholders. The 2005 Plan authorizes the issuance of stock options, stock appreciation rights, unrestricted and restricted stock, phantom shares, dividend equivalent rights, cash-based awards and other equity-based awards. Subject to adjustments upon certain corporate transactions or events, awards with respect to up to a maximum of 27,030,000 fungible units may be granted under the 2005 Plan. Currently, different types of awards count against the limit on the number of fungible units differently, with (1) full-value awards (i.e., those that deliver the full value of the award upon vesting, such as restricted stock) counting as 3.74 Fungible Units per share subject to such awards, (2) stock options, stock appreciation rights and other awards that do not deliver full value and expire five years from the date of grant counting as 0.73 fungible units per share subject to such awards, and (3) all other awards (e.g., ten year stock options) counting as 1.0 fungible units per share subject to such awards. Awards granted under the 2005 Plan prior to the approval of the fourth amendment and restatement in June 2016 continue to count against the fungible unit limit based on the ratios that were in effect at the time such awards were granted, which may be different than the current ratios. As a result, depending on the types of awards issued, the 2005 Plan may result in the issuance of more or less than 27,030,000 shares. If a stock option or other award granted under the 2005 Plan expires or terminates, the common stock subject to any portion of the award that expires or terminates without having been exercised or paid, as the case may be, will again become available for the issuance of additional awards. Shares of our common stock distributed under the 2005 Plan may be treasury shares or authorized but unissued shares. Currently, unless the 2005 Plan has been previously terminated by the Company's board of directors, new awards may be granted under the 2005 Plan until June 2, 2026, which is the tenth anniversary of the date that the 2005 Plan was most recently approved by the Company's stockholders. As of December 31, 2019 , 4.1 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. Stock Options and Class O LTIP Units Options are granted with an exercise price at the fair market value of the Company's common stock on the date of grant and, subject to employment, generally expire five or ten years from the date of grant, are not transferable other than on death, and generally vest in one to five years commencing one year from the date of grant. We have also granted Class O LTIP Units, which are a class of LTIP Units in the Operating Partnership structured to provide economics similar to those of stock options. Class O LTIP Units, once vested, may be converted, at the election of the holder, into a number of common units of the Operating Partnership per Class O LTIP Unit determined by the increase in value of a share of the Company’s common stock at the time of conversion over a participation threshold, which equals the fair market value of a share of the Company’s common stock at the time of grant. Class O LTIP Units are entitled to distributions, subject to vesting, equal per unit to 10% of the per unit distributions paid with respect to the common units of the Operating Partnership. The fair value of each stock option or LTIP Unit granted is estimated on the date of grant using the Black-Scholes option pricing model based on historical information with the following weighted average assumptions for grants during the years ended December 31, 2018 and 2017 . There were no grants during the year ended December 31, 2019 . 2019 2018 2017 Dividend yield none 2.85 % 2.51 % Expected life zero years 3.5 years 4.4 years Risk-free interest rate none 2.48 % 1.73 % Expected stock price volatility none 22.00 % 28.10 % A summary of the status of the Company's stock options as of December 31, 2019 , 2018 , and 2017 and changes during the years ended December 31, 2019 , 2018 , and 2017 are as follows: 2019 2018 2017 Options Outstanding Weighted Average Exercise Price Options Outstanding Weighted Average Exercise Price Options Weighted Balance at beginning of year $ 1,137,017 $ 103.54 $ 1,548,719 $ 101.48 $ 1,737,213 $ 98.44 Granted — — 6,000 97.91 174,000 105.66 Exercised — — (316,302 ) 90.22 (292,193 ) 81.07 Lapsed or canceled (99,949 ) 115.81 (101,400 ) 113.22 (70,301 ) 121.68 Balance at end of year $ 1,037,068 $ 102.36 $ 1,137,017 $ 103.54 $ 1,548,719 $ 101.48 Options exercisable at end of year 914,929 $ 101.69 783,035 $ 101.28 800,902 $ 94.33 Weighted average fair value of options granted during the year $ — $ 84,068 $ 3,816,652 The remaining weighted average contractual life of the options outstanding was 2.7 years and the remaining weighted average contractual life of the options exercisable was 2.7 years. During the years ended December 31, 2019 , 2018 , and 2017 , we recognized compensation expense for these options of $2.5 million , $5.4 million , and $7.8 million , respectively. As of December 31, 2019 , there was $0.1 million of total unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted average period of 0.2 years. Restricted Shares Shares are granted to certain employees, including our executives, and vesting will occur annually upon the completion of a service period or our meeting established financial performance criteria. Annual vesting occurs at rates ranging from 15% to 35% once performance criteria are reached. A summary of the Company's restricted stock as of December 31, 2019 , 2018 , and 2017 and charges during the years ended December 31, 2019 , 2018 , and 2017 are as follows: 2019 2018 2017 Balance at beginning of year 3,452,016 3,298,216 3,202,031 Granted 126,350 162,900 96,185 Canceled (11,900 ) (9,100 ) — Balance at end of year 3,566,466 3,452,016 3,298,216 Vested during the year 113,259 92,114 95,736 Compensation expense recorded $ 12,892,249 $ 12,757,704 $ 9,809,749 Total fair value of restricted stock granted during the year $ 11,131,181 $ 13,440,503 $ 9,905,986 The fair value of restricted stock that vested during the years ended December 31, 2019 , 2018 , and 2017 was $12.1 million , $9.8 million and $9.4 million , respectively. As of December 31, 2019 , there was $20.8 million of total unrecognized compensation cost related to restricted stock, which is expected to be recognized over a weighted average period of 2.0 years . For the years ended December 31, 2019 , 2018 , and 2017 , $2.1 million , $6.3 million , and $7.2 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 $58.3 million and $22.0 million during the years ended December 31, 2019 and 2018 , respectively. The grant date fair value of the LTIP Unit awards was calculated in accordance with ASC 718. A third party consultant determined the fair value of the LTIP Units to have a discount from our common stock price. The discount was calculated by considering the inherent uncertainty that the LTIP Units will reach parity with other common partnership units and the illiquidity due to transfer restrictions. As of December 31, 2019 , there was $31.2 million of total unrecognized compensation expense related to the time-based and performance based LTIP Unit awards, which is expected to be recognized over a weighted average period of 2.3 years. During the years ended December 31, 2019 , 2018 , and 2017 , we recorded compensation expense related to bonus, time-based and performance based LTIP Unit awards of $22.2 million , $24.4 million, and $26.1 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 during the years ended December 31, 2019 and 2018 , and compensation expense of $13.6 million during the year ended December 31, 2017 related to the 2014 Outperformance Plan. Deferred Compensation Plan for Directors Under our Non-Employee Director's Deferral Program, which commenced July 2004, the Company's non-employee directors may elect to defer up to 100% of their annual retainer fee, chairman fees, meeting fees and annual stock grant. Unless otherwise elected by a participant, fees deferred under the program shall be credited in the form of phantom stock units. The program provides that a director's phantom stock units generally will be settled in an equal number of shares of common stock upon the earlier of (i) the January 1 coincident with or the next following such director's termination of service from the Board of Directors or (ii) a change in control by us, as defined by the program. Phantom stock units are credited to each non-employee director quarterly using the closing price of our common stock on the first business day of the respective quarter. Each participating non-employee director is also credited with dividend equivalents or phantom stock units based on the dividend rate for each quarter, which are either paid in cash currently or credited to the director’s account as additional phantom stock units. During the year ended December 31, 2019 , 18,669 phantom stock units and 9,949 shares of common stock were issued to our board of directors. We recorded compensation expense of $2.4 million during the year ended December 31, 2019 related to the Deferred Compensation Plan. As of December 31, 2019 , there were 128,946 phantom stock units outstanding pursuant to our Non-Employee Director's Deferral Program. Employee Stock Purchase Plan In 2007, the Company's board of directors adopted the 2008 Employee Stock Purchase Plan, or ESPP, to encourage our employees to make our business more successful by providing equity-based incentives to eligible employees. The ESPP is intended to qualify as an "employee stock purchase plan" under Section 423 of the Code, and has been adopted by the board to enable our eligible employees to purchase the Company's shares of common stock through payroll deductions. The ESPP became effective on January 1, 2008 with a maximum of 500,000 shares of the common stock available for issuance, subject to adjustment upon a merger, reorganization, stock split or other similar corporate change. The Company filed a registration statement on Form S-8 with the SEC with respect to the ESPP. The common stock is offered for purchase through a series of successive offering periods. Each offering period will be three months in duration and will begin on the first day of each calendar quarter, with the first offering period having commenced on January 1, 2008. The ESPP provides for eligible employees to purchase the common stock at a purchase price equal to 85% of the lesser of (1) the market value of the common stock on the first day of the offering period or (2) the market value of the common stock on the last day of the offering period. The ESPP was approved by our stockholders at our 2008 annual meeting of stockholders. As of December 31, 2019 , 131,440 shares of our common stock had been issued under the ESPP.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Accumulated Other Comprehensive Income	Accumulated Other Comprehensive (Loss) Income The following tables set forth the changes in accumulated other comprehensive (loss) income by component as of December 31, 2019 , 2018 and 2017 (in thousands): Net unrealized gain (loss) on derivative instruments ( 1 ) SL Green’s share of joint venture net unrealized gain (loss) on derivative instruments ( 2 ) Net unrealized gain on marketable securities Total Balance at December 31, 2016 $ 12,596 $ 4,021 $ 5,520 $ 22,137 Other comprehensive (loss) income before reclassifications (1,618 ) 233 (1,348 ) (2,733 ) Amounts reclassified from accumulated other comprehensive income 1,564 766 (3,130 ) (800 ) Balance at December 31, 2017 12,542 5,020 1,042 18,604 Other comprehensive (loss) income before reclassifications (2,252 ) (103 ) 51 (2,304 ) Amounts reclassified from accumulated other comprehensive income (574 ) (618 ) — (1,192 ) Balance at December 31, 2018 9,716 4,299 1,093 15,108 Other comprehensive (loss) income before reclassifications (32,723 ) (11,956 ) 1,184 (43,495 ) Amounts reclassified from accumulated other comprehensive loss 227 (325 ) — (98 ) Balance at December 31, 2019 $ (22,780 ) $ (7,982 ) $ 2,277 $ (28,485 ) (1) Amount reclassified from accumulated other comprehensive (loss) income is included in interest expense in the respective consolidated statements of operations. As of December 31, 2019 and 2018 , the deferred net (gains) losses from these terminated hedges, which is included in accumulated other comprehensive loss relating to net unrealized gain (loss) on derivative instrument, was $(0.7) million and $1.3 million , respectively. (2) Amount reclassified from accumulated other comprehensive (loss) income is included in equity in net (loss) income from unconsolidated joint ventures in the respective consolidated statements of operations.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements We are required to disclose fair value information with regard to our financial instruments, whether or not recognized in the consolidated balance sheets, for which it is practical to estimate fair value. The FASB guidance defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. We measure and/or disclose the estimated fair value of financial assets and liabilities based on a hierarchy that distinguishes between market participant assumptions based on market data obtained from sources independent of the reporting entity and the reporting entity’s own assumptions about market participant assumptions. This hierarchy consists of three broad levels: Level 1 - quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the measurement date; Level 2 - inputs other than quoted prices included within Level 1, that are observable for the asset or liability, either directly or indirectly; and Level 3 - unobservable inputs for the asset or liability that are used when little or no market data is available. We follow this hierarchy for our assets and liabilities measured at fair value on a recurring and nonrecurring basis. In instances in which the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level of input that is significant to the fair value measurement in its entirety. Our assessment of the significance of the particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability. The following tables set forth the assets and liabilities that we measure at fair value on a recurring and non-recurring basis by their levels in the fair value hierarchy at December 31, 2019 and 2018 (in thousands): December 31, 2019 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 29,887 $ — $ 29,887 $ — Interest rate cap and swap agreements (included in other assets) $ 4,419 $ — $ 4,419 $ — Liabilities: Interest rate cap and swap agreements (included in other liabilities) $ 29,110 $ — $ 29,110 $ — December 31, 2018 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 28,638 $ — $ 28,638 $ — Interest rate cap and swap agreements (included in other assets) $ 18,676 $ — $ 18,676 $ — Liabilities: Interest rate cap and swap agreements (included in other liabilities) $ 7,663 $ — $ 7,663 $ — We evaluate for potential impairment in real estate investments and debt and preferred equity investments, including intangibles, primarily utilizing cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as sales comparison approach, which utilizes comparable sales, listings and sales contracts. All of which are classified as Level 3 inputs. In December 2018, the Company determined that it was more likely than not that its Suburban properties would be sold or otherwise disposed of significantly before the end of their previously estimated useful life. The Company tested the recoverability of the assets and, as a result of the carrying amount of the assets not being deemed recoverable and exceeding their fair value as measured on a asset by asset basis, recorded a $221.9 million impairment loss. These charges are included in depreciable real estate reserves and impairment in the consolidated statement of operations. The fair value of the assets were determined primarily utilizing cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as sales comparison approach, which utilizes comparable sales, listings and sales contracts. All of which are classified as Level 3 inputs. In May 2018, the Company was the successful bidder at the foreclosure of 2 Herald Square, at which time the Company's $250.5 million outstanding principal balance and $7.7 million accrued interest balance were credited to our equity investment in the property. We recorded the assets acquired and liabilities assumed at fair value. This resulted in the recognition of a fair value adjustment of $8.1 million , which is reflected on the Company's consolidated statements 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 statements of operations. This fair value was determined using a third party valuation which primarily utilized cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as sales comparison approach, which utilizes comparable sales, listings and sales contracts. All of which are classified as Level 3 inputs. Marketable securities classified as Level 1 are derived from quoted prices in active markets. The valuation technique used to measure the fair value of marketable securities classified as Level 2 were valued based on quoted market prices or model driven valuations using the significant inputs derived from or corroborated by observable market data. Marketable securities in an unrealized loss position are not considered to be other than temporarily impaired. We do not intend to sell these securities and it is not more likely than not that we will be required to sell the investments before recovery of their amortized cost bases. The fair value of derivative instruments is based on current market data received from financial sources that trade such instruments and are based on prevailing market data and derived from third party proprietary models based on well-recognized financial principles and reasonable estimates about relevant future market conditions, which are classified as Level 2 inputs. The financial assets and liabilities that are not measured at fair value on our consolidated balance sheets include cash and cash equivalents, restricted cash, accounts receivable, accounts payable and accrued expenses, debt and preferred equity investments, mortgages and other loans payable and other secured and unsecured debt. The carrying amount of cash and cash equivalents, restricted cash, accounts receivable, and accounts payable and accrued expenses reported in our consolidated balance sheets approximates fair value due to the short term nature of these instruments. The fair value of debt and preferred equity investments, which is classified as Level 3, is estimated by discounting the future cash flows using current interest rates at which similar loans with the same maturities would be made to borrowers with similar credit ratings. The fair value of borrowings, which is classified as Level 3, is estimated by discounting the contractual cash flows of each debt instrument to their present value using adjusted market interest rates, which is provided by a third-party specialist. The following table provides the carrying value and fair value of these financial instruments as of December 31, 2019 and December 31, 2018 (in thousands): December 31, 2019 December 31, 2018 Carrying Value (1) Fair Value Carrying Value (1) Fair Value Debt and preferred equity investments $ 1,580,306 (2) $ 2,099,393 (2) Fixed rate debt $ 3,536,286 $ 3,642,770 $ 3,543,476 $ 3,230,127 Variable rate debt 2,018,434 2,018,714 2,048,442 2,057,966 $ 5,554,720 $ 5,661,484 $ 5,591,918 $ 5,288,093 (1) Amounts exclude net deferred financing costs. (2) At December 31, 2019 , debt and preferred equity investments had an estimated fair value ranging between $1.6 billion and $1.7 billion . At December 31, 2018 , debt and preferred equity investments had an estimated fair value ranging between $2.1 billion and $2.3 billion . Disclosure about fair value of financial instruments was based on pertinent information available to us as of December 31, 2019 and 2018 . Although we are not aware of any factors that would significantly affect the reasonable fair value amounts, such amounts have not been comprehensively revalued for purposes of these financial statements since that date and current estimates of fair value may differ significantly from the amounts presented herein.

Financial Instruments_ Derivati

Financial Instruments: Derivatives and Hedging	12 Months Ended
	Dec. 31, 2019
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 (loss) until the hedged item is recognized in earnings. Reported net income and equity may increase or decrease prospectively, depending on future levels of interest rates and other variables affecting the fair values of derivative instruments and hedged items, but will have no effect on cash flows. Currently, all of our designated derivative instruments are effective hedging instruments. The following table summarizes the notional value at inception and fair value of our consolidated derivative financial instruments at December 31, 2019 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 (dollars in thousands). Notional Value Strike Rate Effective Date Expiration Date Balance Sheet Location Fair Value Interest Rate Cap $ 300,000 3.750 % May 2019 May 2020 Other Assets $ — Interest Rate Swap 100,000 1.928 % December 2017 November 2020 Other Liabilities (281 ) Interest Rate Swap 100,000 1.934 % December 2017 November 2020 Other Liabilities (286 ) Interest Rate Cap 111,869 3.500 % December 2019 December 2020 Other Assets — Interest Rate Cap 85,000 4.000 % March 2019 March 2021 Other Assets — Interest Rate Swap 200,000 1.131 % July 2016 July 2023 Other Assets 3,015 Interest Rate Swap 100,000 1.161 % July 2016 July 2023 Other Assets 1,404 Interest Rate Swap 150,000 2.696 % January 2019 January 2024 Other Liabilities (6,570 ) Interest Rate Swap 150,000 2.721 % January 2019 January 2026 Other Liabilities (9,344 ) Interest Rate Swap 200,000 2.740 % January 2019 January 2026 Other Liabilities (12,629 ) $ (24,691 ) During the years ended December 31, 2019 , 2018 , and 2017 , we recorded a $0.1 million loss, a $0.2 million loss, and a $0.5 million loss, respectively, on the changes in the fair value, which is included in interest expense in the consolidated statements of operations. The Company has agreements with each of its derivative counterparties that contain a provision where if the Company defaults on any of its indebtedness, then the Company could also be declared in default on its derivative obligations. As of December 31, 2019 , 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 $29.5 million . As of December 31, 2019 , 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 $30.1 million at December 31, 2019 . Gains and losses on terminated hedges are included in accumulated other comprehensive income (loss), 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 loss will be reclassified into earnings as an adjustment to interest expense in the same periods in which the hedged interest payments affect earnings. We estimate that $0.4 million of the current balance held in accumulated other comprehensive loss will be reclassified into interest expense and $(0.1) million of the portion related to our share of joint venture accumulated other comprehensive loss will be reclassified into equity in net income from unconsolidated joint ventures within the next 12 months. The following table presents the effect of our derivative financial instruments and our share of our joint ventures' derivative financial instruments that are designated and qualify as hedging instruments on the consolidated statements of operations for the years ended December 31, 2019 , 2018 , and 2017 , respectively (in thousands): Amount of Loss Recognized in Other Comprehensive Loss Location of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income Amount of (Loss) Gain Reclassified from Accumulated Other Comprehensive Loss into Income Year Ended Year Ended Derivative 2019 2018 2017 2019 2018 2017 Interest Rate Swaps/Caps $ (33,907 ) $ (2,284 ) $ (2,282 ) Interest expense $ (261 ) $ 1,168 $ 1,816 Share of unconsolidated joint ventures' derivative instruments (10,322 ) (1,788 ) (200 ) Equity in net income from unconsolidated joint ventures 256 1,097 980 $ (44,229 ) $ (4,072 ) $ (2,482 ) $ (5 ) $ 2,265 $ 2,796

Rental Income

Rental Income	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Rental Income	Rental Income The Operating Partnership is the lessor and the sublessor to tenants under operating leases with expiration dates ranging from January 1, 2020 to 2052. The minimum rental amounts due under the leases are generally either subject to scheduled fixed increases or adjustments. The leases generally also require that the tenants reimburse us for increases in certain operating costs and real estate taxes above their base year costs. Approximate future minimum rents to be received over the next five years and thereafter for non-cancelable operating leases in effect at December 31, 2019 for the consolidated properties, including consolidated joint venture properties, and our share of unconsolidated joint venture properties are as follows (in thousands): Consolidated Properties Unconsolidated Properties 2020 $ 799,001 $ 390,725 2021 651,815 397,524 2022 600,912 380,598 2023 536,835 354,621 2024 496,476 325,459 Thereafter 2,938,340 1,986,928 $ 6,023,379 $ 3,835,855 As of December 31, 2018 , under ASC 840, approximate future minimum rents to be received over the next five years and thereafter for non-cancelable operating leases for the consolidated properties, including consolidated joint venture properties, and our share of unconsolidated joint venture properties are as follows (in thousands): Consolidated Properties Unconsolidated Properties 2019 $ 830,336 $ 348,060 2020 765,610 375,228 2021 625,956 380,886 2022 562,250 348,222 2023 500,499 333,501 Thereafter 3,272,014 2,098,995 $ 6,556,665 $ 3,884,892 The components of lease revenues were as follows (in thousands): Twelve Months Ended December 31, 2019 Twelve Months Ended December 31, 2018 Fixed lease payments $ 858,587 $ 858,160 Variable lease payments 120,496 113,596 Total lease payments $ 979,083 $ 971,756 Amortization of acquired above and below-market leases 4,474 6,818 Total rental revenue $ 983,557 $ 978,574

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Benefit Plans	Benefit Plans The building employees are covered by multi-employer defined benefit pension plans and post-retirement health and welfare plans. We participate in the Building Service 32BJ, or Union, Pension Plan and Health Plan. The Pension Plan is a multi-employer, non-contributory defined benefit pension plan that was established under the terms of collective bargaining agreements between the Service Employees International Union, Local 32BJ, the Realty Advisory Board on Labor Relations, Inc. and certain other employees. This Pension Plan is administered by a joint board of trustees consisting of union trustees and employer trustees and operates under employer identification number 13-1879376. The Pension Plan year runs from July 1 to June 30. Employers contribute to the Pension Plan at a fixed rate on behalf of each covered employee. Separate actuarial information regarding such pension plans is not made available to the contributing employers by the union administrators or trustees, since the plans do not maintain separate records for each reporting unit. However, on September 28, 2017, September 28, 2018, and September 27, 2019, the actuary certified that for the plan years beginning July 1, 2017, July 1, 2018, and July 1, 2019, the Pension Plan was in critical status under the Pension Protection Act of 2006. The Pension Plan trustees adopted a rehabilitation plan consistent with this requirement. No surcharges have been paid to the Pension Plan as of December 31, 2019 . For the Pension Plan years ended June 30, 2019 , 2018 , and 2017 , the plan received contributions from employers totaling $290.1 million , $272.3 million , and $257.8 million . Our contributions to the Pension Plan represent less than 5.0% of total contributions to the plan. The Health Plan was established under the terms of collective bargaining agreements between the Union, the Realty Advisory Board on Labor Relations, Inc. and certain other employers. The Health Plan provides health and other benefits to eligible participants employed in the building service industry who are covered under collective bargaining agreements, or other written agreements, with the Union. The Health Plan is administered by a Board of Trustees with equal representation by the employers and the Union and operates under employer identification number 13-2928869. The Health Plan receives contributions in accordance with collective bargaining agreements or participation agreements. Generally, these agreements provide that the employers contribute to the Health Plan at a fixed rate on behalf of each covered employee. For the Health Plan years ended, June 30, 2019 , 2018 , and 2017 , the plan received contributions from employers totaling $1.5 billion , $1.4 billion and $1.3 billion , respectively. Our contributions to the Health Plan represent less than 5.0% of total contributions to the plan. Contributions we made to the multi-employer plans for the years ended December 31, 2019 , 2018 and 2017 are included in the table below (in thousands): Benefit Plan 2019 2018 2017 Pension Plan $ 3,103 $ 3,017 $ 3,856 Health Plan 9,949 9,310 11,426 Other plans 1,108 1,106 1,463 Total plan contributions $ 14,160 $ 13,433 $ 16,745 401(K) Plan In August 1997, we implemented a 401(K) Savings/Retirement Plan, or the 401(K) Plan, to cover eligible employees of ours, and any designated affiliate. The 401(K) Plan permits eligible employees to defer up to 15% of their annual compensation, subject to certain limitations imposed by the Code. The employees' elective deferrals are immediately vested and non-forfeitable upon contribution to the 401(K) Plan. During 2003, we amended our 401(K) Plan to provide for discretionary matching contributions only. For 2019 and 2018 , a matching contribution equal to 100% of the first 4% of annual compensation was made. For 2017 , a matching contribution equal to 50% of the first 6% of annual compensation was made. For the years ended December 31, 2019 and December 31, 2018 , we made matching contributions of $1.6 million and $1.1 million , respectively. For the year ended December 31, 2017 , we made a matching contribution of $1.0 million .

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings As of December 31, 2019 , the Company and the Operating Partnership were not involved in any material litigation nor, to management's knowledge, was any material litigation threatened against us or our portfolio which if adversely determined could have a material adverse impact on us. Environmental Matters Our management believes that the properties are in compliance in all material respects with applicable Federal, state and local ordinances and regulations regarding environmental issues. Management is not aware of any environmental liability that it believes would have a materially adverse impact on our financial position, results of operations or cash flows. Management is unaware of any instances in which it would incur significant environmental cost if any of our properties were sold. Employment Agreements We have entered into employment agreements with certain executives, which expire between January 2021 and January 2022. The minimum cash-based compensation, including base salary and guaranteed bonus payments, associated with these employment agreements total $3.3 million for 2020. Insurance We maintain “all-risk” property and rental value coverage (including coverage regarding the perils of flood, earthquake and terrorism, excluding nuclear, biological, chemical, and radiological terrorism ("NBCR"), within three property insurance programs and liability insurance. Separate property and liability coverage may be purchased on a stand-alone basis for certain assets, such as the development of One Vanderbilt. Additionally, one of our captive insurance companies, Belmont Insurance Company, or Belmont, provides coverage for NBCR terrorist acts above a specified trigger. Belmont's retention is reinsured by our other captive insurance company, Ticonderoga Insurance Company ("Ticonderoga"). If Belmont or Ticonderoga are required to pay a claim under our insurance policies, we would ultimately record the loss to the extent of required payments. However, there is no assurance that in the future we will be able to procure coverage at a reasonable cost. Further, if we experience losses that are uninsured or that exceed policy limits, we could lose the capital invested in the damaged properties as well as the anticipated future cash flows from those properties. Additionally, our debt instruments contain customary covenants requiring us to maintain insurance and we could default under our debt instruments if the cost and/or availability of certain types of insurance make it impractical or impossible to comply with such covenants relating to insurance. Belmont and Ticonderoga provide coverage solely on properties owned by the Company or its affiliates. Furthermore, with respect to certain of our properties, including properties held by joint ventures or subject to triple net leases, insurance coverage is obtained by a third-party and we do not control the coverage. While we may have agreements with such third parties to maintain adequate coverage and we monitor these policies, such coverage ultimately may not be maintained or adequately cover our risk of loss. Belmont had loss reserves of $2.9 million and $4.0 million as of December 31, 2019 and 2018 , respectively. Ticonderoga had no loss reserves as of December 31, 2019 . Ground Lease Arrangements We are a tenant under ground leases for certain properties. These leases have expirations from 2022 to 2114 , or 2043 to 2114 as fully extended. Certain leases offer extension options which we assess against relevant economic factors to determine whether we are reasonably certain of exercising or not exercising the option. Lease payments associated with renewal periods that we are reasonably certain will be exercised, if any, are included in the measurement of the corresponding lease liability and right of use asset. Certain of our ground leases are subject to rent resets, generally based on a percentage of the then fair market value, a fixed amount, or a percentage of the preceding rent at specified future dates. Rent resets will be recognized in the periods in which they are incurred. The table below summarizes our current ground lease arrangements as of December 31, 2019 : Property (1) Year of Current Expiration Year of Final Expiration (2) 1185 Avenue of the Americas 2043 2043 625 Madison Avenue 2022 2054 420 Lexington Avenue 2050 2080 711 Third Avenue (3) 2033 2083 461 Fifth Avenue (4) 2027 2084 1055 Washington Blvd, Stamford, Connecticut 2090 2090 1080 Amsterdam Avenue (5) 2111 2111 30 East 40th Street (5) 2114 2114 Other Various Various (1) All leases are classified as operating leases unless otherwise specified. (2) Reflects exercise of all available renewal options. (3) The Company owns 50% of the fee interest. (4) The Company has an option to purchase the ground lease for a fixed price on a specific date. (5) A portion of the lease is classified as a financing lease. The following is a schedule of future minimum lease payments under financing leases and operating leases with initial terms in excess of one year as of December 31, 2019 (in thousands): Financing leases Operating leases (1) 2020 $ 2,619 $ 31,508 2021 2,794 31,702 2022 2,794 29,548 2023 2,794 27,243 2024 2,819 27,263 Thereafter 814,283 649,289 Total minimum lease payments $ 828,103 $ 796,553 Amount representing interest (783,655 ) Amount discounted using incremental borrowing rate (414,882 ) Lease liabilities $ 44,448 $ 381,671 (1) As of December 31, 2019 , the total minimum sublease rentals to be received in the future under non-cancelable subleases is $1.6 billion . During the twelve months ended December 31, 2019 , we recognized $4.5 million of financing lease costs, of which $3.2 million represented interest and $1.2 million represented amortization of the right-of-use assets. These amounts are included in interest expense, net of interest income and depreciation and amortization in our consolidated statements of operations, respectively. During the twelve months ended December 31, 2019 , we recognized 33.2 million of operating lease costs, which is calculated on a straight-line basis over the remaining lease terms. This amount is included in operating lease rent in our consolidated statements of operations. As of December 31, 2019 , the weighted-average discount rate used to calculate the lease liabilities was 8.49% . As of December 31, 2019 , the weighted-average remaining lease term was 67 years.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Segment Information	Segment Information The Company has two reportable segments, real estate and debt and preferred equity investments. We evaluate real estate performance and allocate resources based on earnings contributions. The primary sources of revenue are generated from tenant rents and escalations and reimbursement revenue. Real estate property operating expenses consist primarily of security, maintenance, utility costs, insurance, real estate taxes and ground rent expense (at certain applicable properties). See Note 5, "Debt and Preferred Equity Investments," for additional details on our debt and preferred equity investments. Selected consolidated results of operations for the years ended December 31, 2019 , 2018 , and 2017 , and selected asset information as of December 31, 2019 and 2018 , regarding our operating segments are as follows (in thousands): Real Estate Segment Debt and Preferred Equity Segment Total Company Total revenues Years ended: December 31, 2019 $ 1,043,405 $ 195,590 $ 1,238,995 December 31, 2018 1,025,900 201,492 1,227,392 December 31, 2017 1,317,602 193,871 1,511,473 Net Income Years ended: December 31, 2019 $ 158,972 $ 132,515 $ 291,487 December 31, 2018 129,253 141,603 270,856 December 31, 2017 (69,294 ) 170,363 101,069 Total assets As of: December 31, 2019 $ 11,063,155 $ 1,703,165 $ 12,766,320 December 31, 2018 10,481,594 2,269,764 12,751,358 Interest costs for the debt and preferred equity segment include actual costs incurred for borrowings on the 2016 MRA and 2017 MRA. Interest is imputed on the investments that do not collateralize the 2016 MRA or 2017 MRA using our weighted average corporate borrowing cost. We also allocate loan loss reserves, net of recoveries, and transaction related costs to the debt and preferred equity segment. We do not allocate marketing, general and administrative expenses to the debt and preferred equity segment since the use of personnel and resources is dependent on transaction volume between the two segments and varies period over period. In addition, we base performance on the individual segments prior to allocating marketing, general and administrative expenses. For the years ended, December 31, 2019 , 2018 , and 2017 marketing, general and administrative expenses totaled $100.9 million , $92.6 million , and $100.5 million respectively. All other expenses, except interest, relate entirely to the real estate assets. There were no transactions between the above two segments.

Quarterly Financial Data of the

Quarterly Financial Data of the Company (unaudited)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data of the Company/Operating Partnership (unaudited)	Quarterly Financial Data of the Company (unaudited) Summarized quarterly financial data for the years ended December 31, 2019 and 2018 was as follows (in thousands, except for per share amounts): 2019 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 308,082 $ 313,634 $ 313,024 $ 304,255 Total expenses (252,712 ) (263,341 ) (258,383 ) (260,328 ) Equity in net loss from unconsolidated joint ventures (11,874 ) (9,864 ) (7,546 ) (5,234 ) Equity in net gain on sale of interest in unconsolidated joint venture/real estate — — 59,015 17,166 Purchase price and other fair value adjustments — 3,799 67,631 (2,041 ) (Loss) gain on sale of real estate, net (19,241 ) 3,541 — (1,049 ) Depreciable real estate reserves and impairment — (7,047 ) — — Noncontrolling interests and preferred unit distributions (3,086 ) (3,827 ) (8,901 ) (5,239 ) Net income attributable to SL Green 21,169 36,895 164,840 47,530 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income (loss) attributable to SL Green common stockholders $ 17,432 $ 33,157 $ 161,103 $ 43,792 Net income attributable to common stockholders per common share—basic $ 0.21 $ 0.40 $ 1.94 $ 0.52 Net income attributable to common stockholders per common share—diluted $ 0.21 $ 0.40 $ 1.94 $ 0.52 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net (loss) income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 (Loss) gain on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions 838 (7,507 ) (8,606 ) (8,319 ) Net (loss) income attributable to SL Green (57,482 ) 91,947 107,293 105,504 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SL Green common stockholders $ (61,219 ) $ 88,209 $ 103,556 $ 101,766 Net (loss) income attributable to common stockholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common stockholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12

Quarterly Financial Data of t_2

Quarterly Financial Data of the Operating Partnership (unaudited)	12 Months Ended
	Dec. 31, 2019
Condensed Income Statements, Captions [Line Items]
Quarterly Financial Data of the Company/Operating Partnership (unaudited)	Quarterly Financial Data of the Company (unaudited) Summarized quarterly financial data for the years ended December 31, 2019 and 2018 was as follows (in thousands, except for per share amounts): 2019 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 308,082 $ 313,634 $ 313,024 $ 304,255 Total expenses (252,712 ) (263,341 ) (258,383 ) (260,328 ) Equity in net loss from unconsolidated joint ventures (11,874 ) (9,864 ) (7,546 ) (5,234 ) Equity in net gain on sale of interest in unconsolidated joint venture/real estate — — 59,015 17,166 Purchase price and other fair value adjustments — 3,799 67,631 (2,041 ) (Loss) gain on sale of real estate, net (19,241 ) 3,541 — (1,049 ) Depreciable real estate reserves and impairment — (7,047 ) — — Noncontrolling interests and preferred unit distributions (3,086 ) (3,827 ) (8,901 ) (5,239 ) Net income attributable to SL Green 21,169 36,895 164,840 47,530 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income (loss) attributable to SL Green common stockholders $ 17,432 $ 33,157 $ 161,103 $ 43,792 Net income attributable to common stockholders per common share—basic $ 0.21 $ 0.40 $ 1.94 $ 0.52 Net income attributable to common stockholders per common share—diluted $ 0.21 $ 0.40 $ 1.94 $ 0.52 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net (loss) income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 (Loss) gain on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions 838 (7,507 ) (8,606 ) (8,319 ) Net (loss) income attributable to SL Green (57,482 ) 91,947 107,293 105,504 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SL Green common stockholders $ (61,219 ) $ 88,209 $ 103,556 $ 101,766 Net (loss) income attributable to common stockholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common stockholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12
SL Green Operating Partnership
Condensed Income Statements, Captions [Line Items]
Quarterly Financial Data of the Company/Operating Partnership (unaudited)	Quarterly Financial Data of the Operating Partnership (unaudited) Summarized quarterly financial data for the years ended December 31, 2019 and 2018 was as follows (in thousands, except for per share amounts): 2019 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 308,082 $ 313,634 $ 313,024 $ 304,255 Total expenses (252,713 ) (263,341 ) (258,383 ) (260,328 ) Equity in net loss from unconsolidated joint ventures (11,874 ) (9,864 ) (7,546 ) (5,234 ) Equity in net gain on sale of interest in unconsolidated joint venture/real estate — — 59,015 17,166 Purchase price and other fair value adjustments — 3,799 67,631 (2,041 ) (Loss) gain on sale of real estate, net (19,241 ) 3,541 — (1,049 ) Depreciable real estate reserves and impairment — (7,047 ) — — Noncontrolling interests and preferred unit distributions (2,091 ) (2,108 ) (591 ) (2,961 ) Net income attributable to SLGOP 22,163 38,614 173,150 49,808 Perpetual preferred units distributions (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income attributable to SLGOP common unitholders $ 18,426 $ 34,876 $ 169,413 $ 46,070 Net income attributable to common unitholders per common share—basic $ 0.21 $ 0.40 $ 1.94 $ 0.52 Net income attributable to common unitholders per common share—diluted $ 0.21 $ 0.40 $ 1.94 $ 0.52 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net (loss) income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 (Loss) gain on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions (2,601 ) (2,710 ) (3,020 ) (3,047 ) Net (loss) income attributable to SLGOP (60,921 ) 96,744 112,879 110,776 Perpetual preferred units distributions (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SLGOP common unitholders $ (64,658 ) $ 93,006 $ 109,142 $ 107,038 Net (loss) income attributable to common unitholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common unitholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	Column A Column B Column C Column D Column E Description Balance at Beginning of Year Additions Charged Against Operations Uncollectible Accounts Written-off/Recovery (1) Balance at End of Year Year Ended December 31, 2019 Tenant and other receivables—allowance $ 15,702 $ 2,760 $ (6,093 ) $ 12,369 Deferred rent receivable—allowance $ 15,457 $ 4,227 $ (7,207 ) $ 12,477 Year Ended December 31, 2018 Tenant and other receivables—allowance $ 18,637 $ 3,726 $ (6,661 ) $ 15,702 Deferred rent receivable—allowance $ 17,207 $ 491 $ (2,241 ) $ 15,457 Year Ended December 31, 2017 Tenant and other receivables—allowance $ 16,592 $ 6,106 $ (4,061 ) $ 18,637 Deferred rent receivable—allowance $ 25,203 $ 2,321 $ (10,317 ) $ 17,207 (1) Includes the effect of properties that were sold and/or deconsolidated within the period.

Schedule III - Real Estate and

Schedule III - Real Estate and Accumulated Depreciation	12 Months Ended
	Dec. 31, 2019
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Abstract]
Schedule III - Real Estate and Accumulated Depreciation	Column A Column B Column C Initial Cost Column D Cost Capitalized Subsequent To Acquisition Column E Gross Amount at Which Carried at Close of Period Column F Column G Column H Column I Description Encumbrances Land Building & Improvements Land Building & Improvements Land Building & Improvements Total Accumulated Depreciation Date of Construction Date Acquired Life on Which Depreciation is Computed 420 Lexington Ave(1) $ 299,165 $ — $ 333,499 $ — $ 192,729 $ — $ 526,228 $ 526,228 $ 151,898 1927 3/1998 Various 711 Third Avenue(1) — 19,844 115,769 — 59,685 19,844 175,454 195,298 52,265 1955 5/1998 Various 555 W. 57th Street(1) — 18,846 140,946 — 544 18,846 141,490 160,336 75,340 1971 1/1999 Various 461 Fifth Avenue(1) — — 88,276 — 19,670 — 107,946 107,946 34,535 1988 10/2003 Various 750 Third Avenue(1) — 51,093 251,523 — 3,449 51,093 254,972 306,065 109,685 1958 7/2004 Various 625 Madison Avenue(1) — — 291,319 — 14,908 — 306,227 306,227 132,531 1956 10/2004 Various 485 Lexington Avenue(1) 450,000 78,282 452,631 — 6,933 78,282 459,564 537,846 197,431 1956 12/2004 Various 609 Fifth Avenue(1) 53,773 36,677 195,481 — 41,197 36,677 236,678 273,355 44,728 1925 6/2006 Various 810 Seventh Avenue(1) — 114,077 550,819 — (83 ) 114,077 550,736 664,813 190,457 1970 1/2007 Various 1185 Avenue of the Americas(1) — — 791,106 — 116,573 — 907,679 907,679 292,739 1969 1/2007 Various 1350 Avenue of the Americas(1) — 90,941 431,517 — (3,792 ) 90,941 427,725 518,666 142,533 1966 1/2007 Various 1-6 Landmark Square(2) 100,000 27,852 161,343 985 8,319 28,837 169,662 198,499 84,164 1973-1984 1/2007 Various 7 Landmark Square(2) — 1,721 8,417 (985 ) (3,939 ) 736 4,478 5,214 1,657 2007 1/2007 Various 1055 Washington Boulevard(2) — 8,386 43,242 — 10,545 8,386 53,787 62,173 21,723 1987 6/2007 Various 1 Madison Avenue(1) — 173,546 672,805 — 22,977 173,546 695,782 869,328 210,128 1960 8/2007 Various 100 Church Street(1) 209,296 34,994 183,932 — 9,181 34,994 193,113 228,107 60,198 1959 1/2010 Various 125 Park Avenue(1) — 120,900 270,598 — 6,869 120,900 277,467 398,367 88,975 1923 10/2010 Various Williamsburg(3) — 6,200 10,158 — — 6,200 10,158 16,358 2,388 2010 12/2010 Various 110 East 42nd Street(1) — 36,196 78,353 — 3,247 36,196 81,600 117,796 21,124 1921 5/2011 Various 400 East 58th Street(1)(4) 39,094 17,549 38,749 — 373 17,549 39,122 56,671 7,091 1929 1/2012 Various 762 Madison Avenue(1)(4) 771 6,153 10,570 — (35 ) 6,153 10,535 16,688 2,151 1910 1/2012 Various 304 Park Avenue(1) — 54,489 90,643 — 630 54,489 91,273 145,762 22,172 1930 6/2012 Various 635 Sixth Avenue(1) — 24,343 88,261 — 166 24,343 88,427 112,770 14,361 1902 9/2012 Various 641 Sixth Avenue(1) — 45,976 77,076 — 141 45,976 77,217 123,193 18,564 1902 9/2012 Various 1080 Amsterdam(1)(5) 35,123 — 47,948 — 10,316 — 58,264 58,264 6,694 1932 10/2012 Various 315 West 33rd Street(1) 250,000 195,834 179,562 — 2,220 195,834 181,782 377,616 30,853 2000-2001 11/2013 Various 752-760 Madison Avenue(1) — 284,286 8,314 — 12,660 284,286 20,974 305,260 2,752 1996/2012 7/2014 Various 719 Seventh Avenue(1)(6) 50,000 41,180 46,232 — (1,693 ) 41,180 44,539 85,719 1,623 1927 7/2014 Various 110 Greene Street(1) — 45,120 228,393 — 2,414 45,120 230,807 275,927 31,147 1910 7/2015 Various 185 Broadway(1)(7) 120,110 45,422 27,865 118 28,282 45,540 56,147 101,687 419 1921 8/2015 Various 30 East 40th Street(1)(8) — 4,652 26,654 — 4,238 4,652 30,892 35,544 3,267 1927 8/2015 Various 133 Greene Street(1) 15,523 3,446 27,542 — 82 3,446 27,624 31,070 827 1900 10/2018 Various 712 Madison Avenue(1)(11) 28,000 7,207 47,397 — 18 7,207 47,415 54,622 1,185 1900/1980 12/2018 Various 106 Spring Street(1) 38,025 — — 14,173 66,052 14,173 66,052 80,225 1,240 1900 4/2019 Various 410 Tenth Avenue(1)(9) 330,820 — — 140,307 363,523 140,307 363,523 503,830 (3,175 ) 1927 5/2019 Various Other(10) — 1,736 16,224 (2 ) 1,460 1,734 17,684 19,418 4,890 Total $ 2,019,700 $ 1,596,948 $ 6,033,164 $ 154,596 $ 999,859 $ 1,751,544 $ 7,033,023 $ 8,784,567 $ 2,060,560 (1) Property located in New York, New York. (2) Property located in Connecticut. (3) Property located in Brooklyn, New York. (4) We own a 90.0% interest in this property. (5) We own a 92.5% interest in this property. (6) We own a 75.0% interest in this property. (7) Properties at 5-7 Dey Street, 183 Broadway, and 185 Broadway were demolished in preparation of the development site for the 185 Broadway project. (8) We own a 60.0% interest in this property. (9) We own a 70.9% interest in this property. (10) Other includes tenant improvements of eEmerge, capitalized interest and corporate improvements. (11) The tenant at this property has an option to purchase the fee interest for a fixed price on a specific date. The changes in real estate for the years ended December 31, 2019 , 2018 and 2017 are as follows (in thousands): 2019 2018 2017 Balance at beginning of year $ 8,513,935 $ 10,206,122 $ 12,743,332 Property acquisitions — 52,939 13,323 Improvements 251,674 267,726 342,014 Retirements/disposals/deconsolidation 18,958 (2,012,852 ) (2,892,547 ) Balance at end of year $ 8,784,567 $ 8,513,935 $ 10,206,122 The aggregate cost of land, buildings and improvements, before depreciation, for Federal income tax purposes at December 31, 2019 was $10.3 billion (unaudited). The changes in accumulated depreciation, exclusive of amounts relating to equipment, autos, and furniture and fixtures, for the years ended December 31, 2019 , 2018 and 2017 are as follows (in thousands): 2019 2018 2017 Balance at beginning of year $ 2,099,137 $ 2,300,116 $ 2,264,694 Depreciation for year 222,867 245,033 347,015 Retirements/disposals/deconsolidation (261,444 ) (446,012 ) (311,593 ) Balance at end of year $ 2,060,560 $ 2,099,137 $ 2,300,116

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include our accounts and those of our subsidiaries, which are wholly-owned or controlled by us. Entities which we do not control through our voting interest and entities which are variable interest entities, but where we are not the primary beneficiary, are accounted for under the equity method. See Note 5, "Debt and Preferred Equity Investments" and Note 6, "Investments in Unconsolidated Joint Ventures." All significant intercompany balances and transactions have been eliminated. We consolidate a VIE in which we are considered the primary beneficiary. The primary beneficiary is the entity that has (i) the power to direct the activities that most significantly impact the entity's economic performance and (ii) the obligation to absorb losses of the VIE or the right to receive benefits from the VIE that could be significant to the VIE. A noncontrolling interest in a consolidated subsidiary is defined as the portion of the equity (net assets) in a subsidiary not attributable, directly or indirectly, to us. Noncontrolling interests are required to be presented as a separate component of equity in the consolidated balance sheet and the presentation of net income is modified to present earnings and other comprehensive income attributed to controlling and noncontrolling interests. We assess the accounting treatment for each joint venture and debt and preferred equity investment. This assessment includes a review of each joint venture or limited liability company agreement to determine the rights provided to each party and whether those rights are protective or participating. For all VIEs, we review such agreements in order to determine which party has the power to direct the activities that most significantly impact the entity's economic performance. In situations where we and our partner approve, among other things, the annual budget, receive a detailed monthly reporting package, meet on a quarterly basis to review the results of the joint venture, review and approve the joint venture's tax return before filing, and approve all leases that cover more than a nominal amount of space relative to the total rentable space at each property, we do not consolidate the joint venture as we consider these to be substantive participation rights that result in shared power of the activities that most significantly impact the performance of the joint venture. Our joint venture agreements typically contain certain protective rights such as requiring partner approval to sell, finance or refinance the property and the payment of capital expenditures and operating expenditures outside of the approved budget or operating plan.
Investment in Commercial Real Estate Properties	Investment in Commercial Real Estate Properties Real estate properties are presented at cost less accumulated depreciation and amortization. Costs directly related to the development or redevelopment of properties are capitalized. Ordinary repairs and maintenance are expensed as incurred; major replacements and betterments, which improve or extend the life of the asset, are capitalized and depreciated over their estimated useful lives. We recognize the assets acquired, liabilities assumed (including contingencies) and any noncontrolling interests in an acquired entity at their respective fair values on the acquisition date. When we acquire our partner's equity interest in an existing unconsolidated joint venture and gain control over the investment, we record the consolidated investment at fair value. The difference between the book value of our equity investment on the purchase date and our share of the fair value of the investment's purchase price is recorded as a purchase price fair value adjustment in our consolidated statements of operations. See Note 3, "Property Acquisitions." We allocate the purchase price of real estate to land and building (inclusive of tenant improvements) and, if determined to be material, intangibles, such as the value of above- and below-market leases and origination costs associated with the in-place leases. We depreciate the amount allocated to building (inclusive of tenant improvements) over their estimated useful lives, which generally range from three to 40 years. We amortize the amount allocated to the above- and below-market leases over the remaining term of the associated lease, which generally range from one to 14 years, and record it as either an increase (in the case of below-market leases) or a decrease (in the case of above-market leases) to rental income. We amortize the amount allocated to the values associated with in-place leases over the expected term of the associated lease, which generally ranges from one to 14 years. If a tenant vacates its space prior to the contractual termination of the lease and no rental payments are being made on the lease, any unamortized balance of the related intangible will be written off. The tenant improvements and origination costs are amortized as an expense over the remaining life of the lease (or charged against earnings if the lease is terminated prior to its contractual expiration date). We assess fair value of the leases based on estimated cash flow projections that utilize appropriate discount and available market information. Estimates of future cash flows are based on a number of factors including the historical operating results, known trends, and market/economic conditions that may affect the property. To the extent acquired leases contain fixed rate renewal options that are below-market and determined to be material, we amortize such below-market lease value into rental income over the renewal period. As of December 31, 2019 , the weighted average amortization period for above-market leases, below-market leases, and in-place lease costs is 1.7 years, 2.8 years, and 3.5 years, respectively. The Company classifies those leases under which the Company is the lessee at lease commencement as finance or operating leases. Leases qualify as finance leases if the lease transfers ownership of the asset at the end of the lease term, the lease grants an option to purchase the asset that we are reasonably certain to exercise, the lease term is for a major part of the remaining economic life of the asset, or the present value of the lease payments exceeds substantially all of the fair value of the asset. Leases that do not qualify as finance leases are deemed to be operating leases. At lease commencement the Company records a lease liability which is measured as the present value of the lease payments and a right of use asset which is measured as the amount of the lease liability and any initial direct costs incurred. The Company applies a discount rate to determine the present value of the lease payments. If the rate implicit in the lease is known, the Company uses that rate. If the rate implicit in the lease is not known, the Company uses a discount rate reflective of the Company’s collateralized borrowing rate given the term of the lease. To determine the discount rate, the Company employs a third party specialist to develop an analysis based primarily on the observable borrowing rates of the Company, other REITs, and other corporate borrowers with long-term borrowings. On the consolidated statements of operations, operating leases are expensed through operating lease rent while financing leases are expensed through amortization and interest expense. On the consolidated balance sheet, financing leases include the amounts previously captioned "Properties under capital lease." When applicable, the Company combines the consideration for lease and non-lease components in the calculation of the value of the lease obligation and right-of-use asset. We incur a variety of costs in the development and leasing of our properties. After the determination is made to capitalize a cost, it is allocated to the specific component of a project that is benefited. Determination of when a development project is substantially complete and capitalization must cease involves a degree of judgment. The costs of land and building under development include specifically identifiable costs. The capitalized costs include, but are not limited to, pre-construction costs essential to the development of the property, development costs, construction costs, interest costs, real estate taxes, salaries and related costs and other costs incurred during the period of development. We consider a construction project as substantially completed and held available for occupancy upon the completion of tenant improvements, but no later than one year after major construction activity ceases. We cease capitalization on the portions substantially completed and occupied or held available for occupancy, and capitalize only those costs associated with the portions under construction.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid investments with maturity of three months or less when purchased to be cash equivalents.
Restricted Cash	Restricted Cash Restricted cash primarily consists of security deposits held on behalf of our tenants, interest reserves, as well as capital improvement and real estate tax escrows required under certain loan agreements.
Fair Value Measurements	We evaluate for potential impairment in real estate investments and debt and preferred equity investments, including intangibles, primarily utilizing cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as sales comparison approach, which utilizes comparable sales, listings and sales contracts. All of which are classified as Level 3 inputs. In December 2018, the Company determined that it was more likely than not that its Suburban properties would be sold or otherwise disposed of significantly before the end of their previously estimated useful life. The Company tested the recoverability of the assets and, as a result of the carrying amount of the assets not being deemed recoverable and exceeding their fair value as measured on a asset by asset basis, recorded a $221.9 million impairment loss. These charges are included in depreciable real estate reserves and impairment in the consolidated statement of operations. The fair value of the assets were determined primarily utilizing cash flow projections that apply, among other things, estimated revenue and expense growth rates, discount rates and capitalization rates, as well as sales comparison approach, which utilizes comparable sales, listings and sales contracts. All of which are classified as Level 3 inputs. In May 2018, the Company was the successful bidder at the foreclosure of 2 Herald Square, at which time the Company's $250.5 million outstanding principal balance and $7.7 million accrued interest balance were credited to our equity investment in the property. We recorded the assets acquired and liabilities assumed at fair value. This resulted in the recognition of a fair value adjustment of $8.1 million , which is reflected on the Company's consolidated statements 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 statements 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. We are required to disclose fair value information with regard to our financial instruments, whether or not recognized in the consolidated balance sheets, for which it is practical to estimate fair value. The FASB guidance defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. We measure and/or disclose the estimated fair value of financial assets and liabilities based on a hierarchy that distinguishes between market participant assumptions based on market data obtained from sources independent of the reporting entity and the reporting entity’s own assumptions about market participant assumptions. This hierarchy consists of three broad levels: Level 1 - quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the measurement date; Level 2 - inputs other than quoted prices included within Level 1, that are observable for the asset or liability, either directly or indirectly; and Level 3 - unobservable inputs for the asset or liability that are used when little or no market data is available. We follow this hierarchy for our assets and liabilities measured at fair value on a recurring and nonrecurring basis. In instances in which the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level of input that is significant to the fair value measurement in its entirety. Our assessment of the significance of the particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability.
Investment in Marketable Securities	Investment in Marketable Securities At acquisition, we designate a security as held-to-maturity, available-for-sale, or trading. As of December 31, 2019 , we did not have any securities designated as held-to-maturity or trading. We account for our available-for-sale securities at fair value pursuant to Accounting Standards Codification, or ASC, 820-10, with the net unrealized gains or losses reported as a component of accumulated other comprehensive income or loss. The cost of marketable securities sold and the amount reclassified out of accumulated other comprehensive income into earnings is determined using the specific identification method. Any unrealized losses that are determined to be other-than-temporary are recognized in earnings up to their credit component.
Investments in Unconsolidated Joint Ventures	Investments in Unconsolidated Joint Ventures We account for our investments in unconsolidated joint ventures under the equity method of accounting in cases where we exercise significant influence over, but do not control, these entities and are not considered to be the primary beneficiary. We consolidate those joint ventures that we control or which are VIEs and where we are considered to be the primary beneficiary. In all these joint ventures, the rights of the joint venture partner are both protective as well as participating. Unless we are determined to be the primary beneficiary in a VIE, these participating rights preclude us from consolidating these VIE entities. These investments are recorded initially at cost, as investments in unconsolidated joint ventures, and subsequently adjusted for equity in net income (loss) and cash contributions and distributions. Equity in net income (loss) from unconsolidated joint ventures is allocated based on our ownership or economic interest in each joint venture and includes adjustments related to basis differences in accounting for the investment. When a capital event (as defined in each joint venture agreement) such as a refinancing occurs, if return thresholds are met, future equity income will be allocated at our increased economic interest. We recognize incentive income from unconsolidated real estate joint ventures as income to the extent it is earned and not subject to a clawback feature. Distributions we receive from unconsolidated real estate joint ventures in excess of our basis in the investment are recorded as offsets to our investment balance if we remain liable for future obligations of the joint venture or may otherwise be committed to provide future additional financial support. None of the joint venture debt is recourse to us. The Company has performance guarantees under a master lease at one joint venture. See Note 6, "Investments in Unconsolidated Joint Ventures." We assess our investments in unconsolidated joint ventures for recoverability, and if it is determined that a loss in value of the investment is other than temporary, we write down the investment to its fair value. We evaluate our equity investments for impairment based on the joint ventures' projected discounted cash flows. We do not believe that the values of any of our equity investments were impaired at December 31, 2019 . We may originate loans for real estate acquisition, development and construction ("ADC loans"), where we expect to receive some of the residual profit from such projects. When the risk and rewards of these arrangements are essentially the same as an investor or joint venture partner, we account for these arrangements as real estate investments under the equity method of accounting for investments. Otherwise, we account for these arrangements consistent with the accounting for our debt and preferred equity investments.
Deferred Lease Costs	Deferred Lease Costs
Deferred Financing Costs	Deferred Financing Costs Deferred financing costs represent commitment fees, legal, title and other third party costs associated with obtaining commitments for financing which result in a closing of such financing. These costs are amortized over the terms of the respective agreements. Unamortized deferred financing costs are expensed when the associated debt is refinanced or repaid before maturity. Costs incurred in seeking financing transactions, which do not close, are expensed in the period in which it is determined that the financing will not close. Deferred financing costs related to a recognized debt liability are presented in the consolidated balance sheet as a direct deduction from the carrying amount of that debt liability.
Revenue Recognition	Revenue Recognition Rental revenue for operating leases is recognized on a straight-line basis over the term of the lease. Rental revenue recognition commences when the leased space is substantially ready for its intended use. To determine whether the leased space is substantially ready for its intended use, management evaluates whether we are or the tenant is the owner of tenant improvements for accounting purposes. When management concludes that we are the owner of tenant improvements, rental revenue recognition begins when the tenant takes possession of the finished space, which is when such tenant improvements are substantially complete. In certain instances, when management concludes that we are not the owner of tenant improvements, rental revenue recognition begins when the tenant takes possession of or controls the space. When management concludes that we are the owner of tenant improvements for accounting purposes, we record amounts funded to construct the tenant improvements as a capital asset. For these tenant improvements, we record amounts reimbursed by tenants as a reduction of the capital asset. When management concludes that the tenant is the owner of tenant improvements for accounting purposes, we record our contribution towards those improvements as a lease incentive, which is included in deferred costs, net on our consolidated balance sheets and amortized as a reduction to rental revenue on a straight-line basis over the term of the lease. The excess of rents recognized over amounts contractually due pursuant to the underlying leases are included in deferred rents receivable on the consolidated balance sheets. In addition to base rent, our tenants also generally will pay variable rent which represents their pro rata share of increases in real estate taxes and operating expenses for the building over a base year. In some leases, in lieu of paying additional rent based upon increases in building operating expenses, the tenant will pay additional rent based upon increases in the wage rate paid to porters over the porters' wage rate in effect during a base year or increases in the consumer price index over the index value in effect during a base year. In addition, many of our leases contain fixed percentage increases over the base rent to cover escalations. Electricity is most often supplied by the landlord either on a sub-metered basis, or rent inclusion basis (i.e., a fixed fee is included in the rent for electricity, which amount may increase based upon increases in electricity rates or increases in electrical usage by the tenant). Base building services other than electricity (such as heat, air conditioning and freight elevator service during business hours, and base building cleaning) are typically provided at no additional cost, with the tenant paying additional rent only for services which exceed base building services or for services which are provided outside normal business hours. These escalations are based on actual expenses incurred in the prior calendar year. If the expenses in the current year are different from those in the prior year, then during the current year, the escalations will be adjusted to reflect the actual expenses for the current year. Rental revenue is recognized if collectability is probable. If collectability of substantially all of the lease payments is assessed as not probable, any difference between the rental revenue recognized to date and the lease payments that have been collected is recognized as a current-period adjustment to rental revenue. A subsequent change in the assessment of collectability to probable may result in a current-period adjustment to rental revenue for any difference between the rental revenue that would have been recognized if collectability had always been assessed as probable and the rental revenue recognized to date. The Company provides its tenants with certain customary services for lease contracts such as common area maintenance and general security. We have elected to combine the nonlease components with the lease components of our operating lease agreements and account for them as a single lease component in accordance with ASC 842. We record a gain or loss on sale of real estate assets when we no longer hold a controlling financial interest in the entity holding the real estate, a contract exists with a third party and that third party has control of the assets acquired. Investment income on debt and preferred equity investments is accrued based on the contractual terms of the instruments and when, in the opinion of management, it is deemed collectible. Some debt and preferred equity investments provide for accrual of interest at specified rates, which differ from current payment terms. Interest is recognized on such loans at the accrual rate subject to management's determination that accrued interest is collectible. If management cannot make this determination, interest income above the current pay rate is recognized only upon actual receipt. Deferred origination fees, original issue discounts and loan origination costs, if any, are recognized as an adjustment to interest income over the terms of the related investments using the effective interest method. Fees received in connection with loan commitments are also deferred until the loan is funded and are then recognized over the term of the loan as an adjustment to yield. Discounts or premiums associated with the purchase of loans are amortized or accreted into interest income as a yield adjustment on the effective interest method based on expected cash flows through the expected maturity date of the related investment. If we purchase a debt or preferred equity investment at a discount, intend to hold it until maturity and expect to recover the full value of the investment, we accrete the discount into income as an adjustment to yield over the term of the investment. If we purchase a debt or preferred equity investment at a discount with the intention of foreclosing on the collateral, we do not accrete the discount. For debt investments acquired at a discount for credit quality, the difference between contractual cash flows and expected cash flows at acquisition is not accreted. Anticipated exit fees, the collection of which is expected, are also recognized over the term of the loan as an adjustment to yield. Debt and preferred equity investments are placed on a non-accrual status at the earlier of the date at which payments become 90 days past due or when, in the opinion of management, a full recovery of interest income becomes doubtful. Interest income recognition on any non-accrual debt or preferred equity investment is resumed when such non-accrual debt or preferred equity investment becomes contractually current and performance is demonstrated to be resumed. Interest is recorded as income on impaired loans only to the extent cash is received. We may syndicate a portion of the loans that we originate or sell the loans individually. When a transaction meets the criteria for sale accounting, we recognize gain or loss based on the difference between the sales price and the carrying value of the loan sold. Any related unamortized deferred origination fees, original issue discounts, loan origination costs, discounts or premiums at the time of sale are recognized as an adjustment to the gain or loss on sale, which is included in investment income on the consolidated statement of operations. Any fees received at the time of sale or syndication are recognized as part of investment income. Asset management fees are recognized on a straight-line basis over the term of the asset management agreement.
Allowance for Loan Loss and Other Investment Reserves	Allowance for Loan Loss and Other Investment Reserves The expense for loan loss and other investment reserves in connection with debt and preferred equity investments is the charge to earnings to adjust the allowance for possible losses to the level that we estimate to be adequate, based on Level 3 data, considering delinquencies, loss experience and collateral quality. The Company evaluates debt and preferred equity investments that are classified as held to maturity for possible impairment or credit deterioration associated with the performance and/or value of the underlying collateral property as well as the financial and operating capability of the borrower/sponsor. Quarterly, the Company assigns each loan a risk rating. Based on a 3-point scale, loans are rated “1” through “3,” from less risk to greater risk, which ratings are defined as follows: 1 - Low Risk Assets - Low probability of loss, 2 - Watch List Assets - Higher potential for loss, 3 - High Risk Assets - Loss more likely than not. When it is probable that we will be unable to collect all amounts contractually due, the investment is considered impaired. A valuation allowance is measured based upon the excess of the carrying value of the investment over the fair value of the collateral. Any deficiency between the carrying value of an asset and the calculated value of the collateral is charged to expense. We continue to assess or adjust our estimates based on circumstances of a loan and the underlying collateral. If additional information reflects increased recovery of our investment, we will adjust our reserves accordingly. Debt and preferred equity investments that are classified as held for sale are carried at the lower of cost or fair market value using available market information obtained through consultation with dealers or other originators of such investments as well as discounted cash flow models based on Level 3 data pursuant to ASC 820-10. As circumstances change, management may conclude not to sell an investment designated as held for sale. In such situations, the investment will be reclassified at its net carrying value to debt and preferred equity investments held to maturity. For these reclassified investments, the difference between the current carrying value and the expected cash to be collected at maturity will be accreted into income over the remaining term of the investment.
Rent Expense	Rent Expense Rent expense is recognized on a straight-line basis over the initial term of the lease. The excess of the rent expense recognized over the amounts contractually due pursuant to the underlying lease is included in the lease liability - operating leases on the consolidated balance sheets.
Underwriting Commissions and Costs	Underwriting Commissions and Costs Underwriting commissions and costs incurred in connection with our stock offerings are reflected as a reduction of additional paid-in-capital.
Exchangeable Debt Instruments	Exchangeable Debt Instruments The initial proceeds from exchangeable debt that may be settled in cash, including partial cash settlements, are bifurcated between a liability component and an equity component associated with the embedded conversion option. The objective of the accounting guidance is to require the liability and equity components of exchangeable debt to be separately accounted for in a manner such that the interest expense on the exchangeable debt is not recorded at the stated rate of interest but rather at an effective rate that reflects the issuer's conventional debt borrowing rate at the date of issuance. We calculate the liability component of exchangeable debt based on the present value of the contractual cash flows discounted at our comparable market conventional debt borrowing rate at the date of issuance. The difference between the principal amount and the fair value of the liability component is reported as a discount on the exchangeable debt that is accreted as additional interest expense from the issuance date through the contractual maturity date using the effective interest method. A portion of this additional interest expense may be capitalized to the development and redevelopment balances qualifying for interest capitalization each period. The liability component of the exchangeable debt is reported net of discounts on our consolidated balance sheets. We calculate the equity component of exchangeable debt based on the difference between the initial proceeds received from the issuance of the exchangeable debt and the fair value of the liability component at the issuance date. The equity component is included in additional paid-in-capital, net of issuance costs, on our consolidated balance sheets. We allocate issuance costs for exchangeable debt between the liability and the equity components based on their relative values.
Transaction cost	Transaction Costs Transaction costs for asset acquisitions are capitalized to the investment basis, which is then subject to a purchase price allocation based on relative fair value. Transaction costs for business combinations or costs incurred on potential transactions that are not consummated are expensed as incurred.
Income Taxes	Income Taxes SL Green is taxed as a REIT under Section 856(c) of the Code. As a REIT, SL Green generally is not subject to Federal income tax. To maintain its qualification as a REIT, SL Green must distribute at least 90% of its REIT taxable income to its stockholders and meet certain other requirements. If SL Green fails to qualify as a REIT in any taxable year, SL Green will be subject to Federal income tax on its taxable income at regular corporate rates. SL Green may also be subject to certain state, local and franchise taxes. Under certain circumstances, Federal income and excise taxes may be due on its undistributed taxable income. The Operating Partnership is a partnership and, as a result, all income and losses of the partnership are allocated to the partners for inclusion in their respective income tax returns. The only provision for income taxes included in the consolidated statements of operations relates to the Operating Partnership’s consolidated taxable REIT subsidiaries. The Operating Partnership may also be subject to certain state, local and franchise taxes. We have elected, and may elect in the future, to treat certain of our corporate subsidiaries as taxable REIT subsidiaries, or TRSs. In general, TRSs may perform non-customary services for the tenants of the Company, hold assets that we cannot hold directly and generally may engage in any real estate or non-real estate related business. The TRSs generate income, resulting in Federal and state income tax liability for these entities. During the years ended December 31, 2019 , 2018 and 2017 , we recorded Federal, state and local tax provisions of $1.5 million , $2.8 million , and $4.3 million , respectively. For the year ended December 31, 2019 , the Company paid distributions on its common stock of $3.40 per share which represented $2.59 per share of ordinary income and $0.81 per share of capital gains. For the year ended December 31, 2018 , the Company paid distributions on its common stock of $3.25 per share which represented $1.46 per share of ordinary income, and $1.79 per share of capital gains. For the year ended December 31, 2017, the Company paid distributions on its common stock of $3.10 per share which represented $1.24 per share of ordinary income and $1.86 per share of capital gains. 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 made substantial changes to the Code. The Tax Act did not have a material impact on our financial statements for the years ended December 31, 2019 or December 31, 2018 .
Stock-Based Employee Compensation Plans	Stock-Based Employee Compensation Plans We have a stock-based employee compensation plan, described more fully in Note 14, "Share-based Compensation." The Company's stock options are recorded at fair value at the time of issuance. Fair value of the stock options is determined using the Black-Scholes option pricing model. The Black-Scholes model was developed for use in estimating the fair value of traded options, which have no vesting restrictions and are fully transferable. In addition, option valuation models require the input of highly subjective assumptions including the expected stock price volatility. Because our plan has characteristics significantly different from those of traded options and because changes in the subjective input assumptions can materially affect the fair value estimate, in our opinion, the existing models do not necessarily provide a reliable single measure of the fair value of the employee stock options. Compensation cost for stock options, if any, is recognized over the vesting period of the award. Our policy is to grant options with an exercise price equal to the quoted closing market price of the Company's common stock on either the grant date or the date immediately preceding the grant date. Awards of stock or restricted stock are expensed as compensation over the benefit period based on the fair value of the stock on the grant date. For share-based awards with a performance or market measure, we recognize compensation cost over the requisite service period, using the accelerated attribution expense method. The requisite service period begins on the date the compensation committee of our board of directors authorizes the award, adopts any relevant performance measures and communicates the award to the employees. For programs with awards that vest based on the achievement of a performance condition or market condition, we determine whether it is probable that the performance condition will be met, and estimate compensation cost based on the fair value of the award at the applicable award date estimated using a binomial model or market quotes. For share-based awards for which there is no pre-established performance measure, we recognize compensation cost over the service vesting period, which represents the requisite service period, on a straight-line basis. In accordance with the provisions of our share-based incentive compensation plans, we accept the return of shares of the Company's common stock, at the current quoted market price, from certain key employees to satisfy minimum statutory tax-withholding requirements related to shares that vested during the period. Awards can also be made in the form of a separate series of units of limited partnership interest in the Operating Partnership called long-term incentive plan units, or LTIP units. LTIP units, which can be granted either as free-standing awards or in tandem with other awards under our stock incentive plan, are valued by reference to the value of the Company's common stock at the time of grant, and are subject to such conditions and restrictions as the compensation committee of the Company's board of directors may determine, including continued employment or service, computation of financial metrics and/or achievement of pre-established performance goals and objectives.
Derivative Instruments	Derivative Instruments In the normal course of business, we use a variety of commonly used derivative instruments, such as interest rate swaps, caps, collars and floors, to manage, or hedge, interest rate risk. Effectiveness is essential for those derivatives that we intend to qualify for hedge accounting. Some derivative instruments are associated with an anticipated transaction. In those cases, hedge effectiveness criteria also require that it be probable that the underlying transaction occurs. Instruments that meet these hedging criteria are formally designated as hedges at the inception of the derivative contract. To determine the fair values of derivative instruments, we use a variety of methods and assumptions that are based on market conditions and risks existing at each balance sheet date. For the majority of financial instruments including most derivatives, long-term investments and long-term debt, standard market conventions and techniques such as discounted cash flow analysis, option pricing models, replacement cost, and termination cost are used to determine fair value. All methods of assessing fair value result in a general approximation of value, and such value may never actually be realized. In the normal course of business, we are exposed to the effect of interest rate changes and limit these risks by following established risk management policies and procedures including the use of derivatives. To address exposure to interest rates, derivatives are used primarily to fix the rate on debt based on floating-rate indices and manage the cost of borrowing obligations. We use a variety of conventional derivative products. These derivatives typically include interest rate swaps, caps, collars and floors. We expressly prohibit the use of unconventional derivative instruments and using derivative instruments for trading or speculative purposes. Further, we have a policy of only entering into contracts with major financial institutions based upon their credit ratings and other factors. We may employ swaps, forwards or purchased options to hedge qualifying forecasted transactions. Gains and losses related to these transactions are deferred and recognized in net income as interest expense in the same period or periods that the underlying transaction occurs, expires or is otherwise terminated. Hedges that are reported at fair value and presented on the balance sheet could be characterized as cash flow hedges or fair value hedges. Interest rate caps and collars are examples of cash flow hedges. Cash flow hedges address the risk associated with future cash flows of interest payments. For all hedges held by us that meet the hedging objectives established by our corporate policy governing interest rate risk management, no net gains or losses were reported in earnings. The changes in fair value of derivative instruments designated as hedge instruments are reflected in accumulated other comprehensive income (loss). For derivative instruments not designated as hedging instruments, the gain or loss, resulting from the change in the estimated fair value of the derivative instruments, is recognized in current earnings during the period of change.
Earnings per Share of the Company	Earnings per Share of the Company The Company presents both basic and diluted earnings per share, or EPS, using the two-class method, which is an earnings allocation formula that determines EPS for common stock and any participating securities according to dividends declared (whether paid or unpaid). Under the two-class method, basic EPS is computed by dividing the income available to common stockholders by the weighted-average number of common stock shares outstanding for the period. Basic EPS includes participating securities, consisting of unvested restricted stock that receive nonforfeitable dividends similar to shares of common stock. Diluted EPS reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock, where such exercise or conversion would result in a lower EPS amount. Diluted EPS also includes units of limited partnership interest. The dilutive effect of stock options is reflected in the weighted average diluted outstanding shares calculation by application of the treasury stock method. There was no dilutive effect for the exchangeable senior notes as the conversion premium was to be paid in cash.
Earnings per Unit of the Operating Partnership	Earnings per Unit of the Operating Partnership The Operating Partnership presents both basic and diluted earnings per unit, or EPU, using the two-class method, which is an earnings allocation formula that determines EPU for common units and any participating securities according to dividends declared (whether paid or unpaid). Under the two-class method, basic EPU is computed by dividing the income available to common unitholders by the weighted-average number of common units outstanding for the period. Basic EPU includes participating securities, consisting of unvested restricted units that receive nonforfeitable dividends similar to shares of common units. Diluted EPU reflects the potential dilution that could occur if securities or other contracts to issue common units were exercised or converted into common units, where such exercise or conversion would result in a lower EPU amount. The dilutive effect of unit options is reflected in the weighted average diluted outstanding units calculation by application of the treasury stock method. There was no dilutive effect for the exchangeable senior notes as the conversion premium was to be paid in cash.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash investments, debt and preferred equity investments and accounts receivable. We place our cash investments with high quality financial institutions. The collateral securing our debt and preferred equity investments is located in the New York metropolitan area. See Note 5, "Debt and Preferred Equity Investments."
Reclassification	Reclassification Certain prior year balances have been reclassified to conform to our current year presentation.
Accounting Standards Updates	Accounting Standards Updates In August 2018, the FASB issued Accounting Standard Update, or ASU, No. 2018-15, Intangibles - Goodwill and Other- Internal-Use Software (Topic 350-40), Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract. The amendments provide guidance on accounting for fees paid when the arrangement includes a software license and align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing costs to develop or obtain internal-use software. The guidance is effective for the Company for fiscal years beginning after December 15, 2019. Early adoption is permitted. The Company has not yet adopted this new guidance and does not expect it to have a material impact on the Company’s consolidated financial statements when the new standard is implemented. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820), Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. This amendment removed, modified and added the disclosure requirements under Topic 820. The changes are effective for the Company for fiscal years beginning after December 15, 2019. Early adoption is permitted for the removed or modified disclosures with adoption of the additional disclosures upon the effective date. The Company has not yet adopted this new guidance and does not expect it to have a material impact on the Company’s consolidated financial statements when the new standard is implemented. In June 2018, the FASB issued ASU No. 2018-07, Compensation - Stock Compensation (Topic 718), Improvements to Nonemployee Share-Based Payment Accounting and in November 2019, issued ASU No. 2019-08, Compensation Stock Compensation (Topic 718) and Revenue from Contracts with Customers (Topic 606). These amendments provide additional guidance related to share-based payment transactions for acquiring goods or services from nonemployees. The Company has adopted this guidance in 2019 and it did not have a material impact on the Company’s consolidated financial statements. In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities; in July 2018, the FASB issued ASU No. 2018-16, Derivatives and Hedging (Topic 815): Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes; and in May 2019, issued ASU No. 2019-05, Codification Improvements. The amendments in the new standards will permit more flexibility in hedging interest rate risk for both variable rate and fixed rate financial instruments. The standards will also enhance the presentation of hedge results in the financial statements. The Company adopted this guidance on January 1, 2019, and it did not have a material impact on the Company’s consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments; in November 2018 issued ASU No. 2018-19, Codification Improvements to Topic 326, Financial Instruments - Credit Losses, in April, May and November 2019, issued ASU No. 2019-04, 2019-05 and 2019-11, which provide codification improvements and targeted transition relief. 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. The Company’s DPE portfolio and financing lease assets will be subject to this guidance once the Company adopts it. ASU No. 2018-19 excludes operating lease receivables from the scope of this guidance. The Company will adopt this guidance January 1, 2020 and does not expect it to have a material impact on the Company’s consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases. In July 2018, the FASB issued ASU No. 2018-10 - Codification Improvements to Topic 842, Leases, and ASU No. 2018-11 - Targeted Improvements. In December 2018, the FASB issued ASU No. 2018-20 - Narrow-Scope Improvements for Lessors and in March 2019 issued ASU No. 2019-01 - Codification Improvements. The Company adopted this guidance on January 1, 2019 using the modified retrospective approach which allows the Company to apply the guidance for the current year presentation and not adjust the prior year numbers. The Company elected the package of practical expedients that allows an entity to not reassess (i) whether any expired or existing contracts are or contain leases, (ii) lease classification for any expired or existing leases and (iii) initial direct costs for any expired or existing leases. The new guidance applies to the ground leases under which the Company is a lessee. The Company has recognized a new asset and liability - “Right of use asset - operating leases” and “Lease liability - operating leases” - for those leases classified as operating leases under the previous standard. The Company will continue to recognize expense on a straight-line basis for these operating leases. The ground leases that the Company historically reported as “Properties under capital leases” and “Capitalized lease obligations” are now labeled “Right of use asset - financing leases” and “Lease liability - financing leases”. The expense recognition of these leases has not changed. The Company adopted the practical expedient offered in ASU No. 2018-11 that allows lessors to not separate non-lease components from the related lease components under certain conditions. In doing so, the Company has collapsed the line “Escalation and reimbursement revenues” into the “Rental revenue, net” line to reflect adopting this practical expedient. The Company also collapsed the prior year balances to conform to the current year presentation. For future leases, the Company no longer capitalizes internal leasing costs that are not incremental and direct as defined under the new guidance. The Company has recorded additional expense of approximately $10.0 million related to this change for the year ended December 31, 2019 .

Organization and Basis of Pre_2

Organization and Basis of Presentation (Tables)	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of commercial office properties	As of December 31, 2019 , we owned the following interests in properties in the New York metropolitan area, primarily in midtown Manhattan. Our investments located outside of Manhattan are referred to as the Suburban properties: Consolidated Unconsolidated Total Location Property Type Number of Properties Approximate Square Feet (unaudited) Number of Properties Approximate Square Feet (unaudited) Number of Properties Approximate Square Feet (unaudited) Weighted Average Occupancy (1) (unaudited) Commercial: Manhattan Office 20 12,387,091 10 11,216,183 30 23,603,274 94.5 % Retail 6 (2) 320,430 8 289,050 14 609,480 98.4 % Development/Redevelopment (3) 6 189,538 1 — 7 189,538 84.9 % Fee Interest — — 1 — 1 — — % 32 12,897,059 20 11,505,233 52 24,402,292 94.6 % Suburban Office 8 1,044,800 — — 8 1,044,800 85.7 % Retail 1 52,000 — — 1 52,000 100.0 % 9 1,096,800 — — 9 1,096,800 86.4 % Total commercial properties 41 13,993,859 20 11,505,233 61 25,499,092 94.2 % Residential: Manhattan Residential 2 (2) 445,105 8 1,663,774 10 2,108,879 95.7 % Total residential properties 2 445,105 8 1,663,774 10 2,108,879 95.7 % Total portfolio 43 14,438,964 28 13,169,007 71 27,607,971 94.3 % (1) The weighted average occupancy for commercial properties represents the total occupied square footage divided by the total square footage at acquisition. The weighted average occupancy for residential properties represents the total occupied units divided by the total available units. (2) As of December 31, 2019 , 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. (3) Properties in Development are included in Number of Properties with no Approximate Square Feet.

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Schedule of estimated useful lives	Properties other than Right of use assets - operating leases are depreciated using the straight-line method over the estimated useful lives of the assets. The estimated useful lives are as follows: Category Term Building (fee ownership) 40 years Building improvements shorter of remaining life of the building or useful life Building (leasehold interest) lesser of 40 years or remaining term of the lease Right of use assets - financing leases lesser of 40 years or remaining lease term Furniture and fixtures four to seven years Tenant improvements shorter of remaining term of the lease or useful life
Summary of identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases)	The following summarizes our identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases) as of December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Identified intangible assets (included in other assets): Gross amount $ 255,198 $ 266,540 Accumulated amortization (228,223 ) (241,040 ) Net (1) $ 26,975 $ 25,500 Identified intangible liabilities (included in deferred revenue): Gross amount $ 282,048 $ 276,245 Accumulated amortization (249,514 ) (253,767 ) Net (1) $ 32,534 $ 22,478 (1) As of December 31, 2019 , no net intangible assets and no net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale. As of December 31, 2018 , no net intangible assets and no net intangible liabilities were reclassified to assets held for sale and liabilities related to assets held for sale.
Schedule of estimated annual amortization of acquired above-market leases, net of acquired below-market leases	The estimated annual amortization of acquired above-market leases, net of acquired (below-market) leases (a component of rental revenue), for each of the five succeeding years is as follows (in thousands): 2020 $ (4,320 ) 2021 (2,748 ) 2022 (2,224 ) 2023 (1,301 ) 2024 (834 )
Schedule of estimated annual amortization of all other identifiable assets	The estimated annual amortization of all other identifiable assets (a component of depreciation and amortization expense) including tenant improvements for each of the five succeeding years is as follows (in thousands): 2020 $ 5,183 2021 3,638 2022 2,064 2023 1,435 2024 1,040
Schedule of marketable securities	At December 31, 2019 and 2018 , we held the following marketable securities (in thousands): December 31, 2019 2018 Commercial mortgage-backed securities $ 29,887 $ 28,638 Total marketable securities available-for-sale $ 29,887 $ 28,638
Schedules of concentration of risk, by risk factor	For the years ended December 31, 2019, 2018, and 2017, the following properties contributed more than 5.0% of our annualized cash rent from office properties, including our share of annualized cash rent from joint venture office properties: Property 2019 Property 2018 Property 2017 1185 Avenue of the Americas 7.6% 11 Madison Avenue 7.4% 11 Madison Avenue 7.1% 11 Madison Avenue 7.4% 1185 Avenue of the Americas 6.7% 1185 Avenue of the Americas 7.1% 420 Lexington Avenue 6.6% 420 Lexington Avenue 6.5% 1515 Broadway 7.0% 1515 Broadway 6.1% 1515 Broadway 6.0% 420 Lexington Avenue 6.0% One Madison Avenue 6.0% One Madison Avenue 5.8% One Madison Avenue 5.6% 220 East 42 nd Street 5.5%

Property Acquisitions (Tables)

Property Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2019
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition	The following table summarizes the properties acquired during the year ended December 31, 2019 : Property Acquisition Date Property Type Approximate Square Feet Gross Asset Valuation (in millions) 106 Spring Street (1) April 2019 Fee Interest 5,928 $ 80.2 410 Tenth Avenue (2) May 2019 Fee Interest 638,000 440.0 110 Greene Street (3) May 2019 Fee Interest 223,600 256.5 (1) In April 2019, the Company accepted an assignment of the equity interests in the property in lieu of repayment of the Company's debt investment and marked the assets received and liabilities assumed to fair value. (2) In May 2019, the Company closed on the acquisition of a majority and controlling 70.87% interest in 410 Tenth Avenue. We recorded the assets acquired and liabilities assumed at fair value, which resulted in the recognition of a fair value adjustment of $67.6 million, which is reflected in the Company's consolidated statement of operations within purchase price and other fair value adjustments, and $18.3 million of net intangible lease liabilities. (3) In May 2019, the Company acquired from our joint venture partner the remaining 10% interest in this property that the Company did not already own. 2018 Acquisitions The following table summarizes the properties acquired during the year ended December 31, 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 1231 Third Avenue (2)(3) July 2018 Fee Interest 39,000 55.4 Upper East Side Residential (3)(4) August 2018 Fee Interest 0.2 acres 30.2 133 Greene Street (2) October 2018 Fee Interest 6,425 31.0 712 Madison Avenue (2) December 2018 Fee Interest 6,600 58.0 (1) In May 2018, the Company was the successful bidder at the foreclosure of the asset. We recorded the assets acquired and liabilities assumed at fair value. This resulted in the recognition of a fair value adjustment of $8.1 million , which is reflected in the Company's consolidated statement of operations within purchase price and other fair value adjustments. See Note 16, "Fair Value Measurements." The Company subsequently sold a 49% interest in the property in November 2018. See Note 4, "Properties Held for Sale and Dispositions." and Note 6, "Investments in Unconsolidated Joint Ventures." (2) The Company accepted an assignment of the equity interests in the property in lieu of repayment of the Company's debt investment, and recorded the assets received and liabilities assumed at fair value. (3) This property was subsequently sold in October 2018. See Note 4, "Properties Held for Sale and Dispositions." (4) In August 2018, the Company acquired the fee interest in three additional land parcels at the Upper East Side Residential Assemblage.

Properties Held for Sale and _2

Properties Held for Sale and Property Dispositions (Tables)	12 Months Ended
	Dec. 31, 2019
Discontinued Operations and Disposal Groups [Abstract]
Summary of properties sold and income from discontinued operations	The following table summarizes the properties sold during the years ended December 31, 2019 , 2018 , and 2017 : Property Disposition Date Property Type Unaudited Approximate Usable Square Feet Sales Price (1) (in millions) Gain (Loss) on Sale (2) (in millions) Suburban Properties (3) December 2019 Fee Interest 1,107,000 $ 229.2 $ 1.8 1640 Flatbush Avenue December 2019 Fee Interest 1,000 16.2 5.5 562 Fifth Avenue December 2019 Fee Interest 42,635 52.4 (26.6 ) 1010 Washington Boulevard November 2019 Fee Interest 143,400 23.1 (7.1 ) 115 Spring Street (4) August 2019 Fee Interest 5,218 66.6 3.6 2 Herald Square (5) November 2018 Office/Retail 369,000 265.0 — 400 Summit Lake Drive November 2018 Land 39.5 acres 3.0 (36.2 ) Upper East Side Assemblage (6)(7) October 2018 Development 70,142 143.8 (6.3 ) 1-6 International Drive July 2018 Office 540,000 55.0 (2.6 ) 635 Madison Avenue June 2018 Retail 176,530 153.0 (14.1 ) 115-117 Stevens Avenue May 2018 Office 178,000 12.0 (0.7 ) 600 Lexington Avenue January 2018 Office 303,515 305.0 23.8 1515 Broadway (8) December 2017 Office 1,750,000 1,950.0 — 125 Chubb Way October 2017 Office 278,000 29.5 (26.1 ) 16 Court Street October 2017 Office 317,600 171.0 64.9 680-750 Washington Boulevard July 2017 Office 325,000 97.0 (44.2 ) 520 White Plains Road April 2017 Office 180,000 21.0 (14.6 ) 102 Greene Street (9) April 2017 Retail 9,200 43.5 4.9 (1) Sales price represents the gross sales price for a property or the gross asset valuation for interests in a property. (2) The gain on sale for 1640 Flatbush Avenue, 600 Lexington Avenue, 16 Court Street, and 102 Greene Street are net of $2.0 million , $1.3 million , $2.5 million , and $0.9 million , respectively, in employee compensation accrued in connection with the realization of these investment gains. Additionally, amounts do not include adjustments for expenses recorded in subsequent periods. (3) Suburban Properties consists of 360 Hamilton Avenue, 100 Summit Lake Drive, 200 Summit Lake Drive, and 500 Summit Lake Drive. (4) The Company sold a 49% interest, which resulted in the deconsolidation of our remaining 51% interest. We recorded our investment at fair value which resulted in the recognition of a fair value adjustment of $3.8 million , which is reflected in the Company's consolidated statements of operations within purchase price and other fair value adjustments. See Note 6, "Investments in Unconsolidated Joint Ventures." (5) In November 2018, the Company sold a 49% interest in 2 Herald Square to an Israeli institutional investor. See Note 6, "Investments in Unconsolidated Joint Ventures." (6) Upper East Side Assemblage consists of 260 East 72nd Street, 31,076 square feet of development rights, 252-254 East 72nd Street, 257 East 71st Street, 259 East 71st Street, and 1231 Third Avenue. (7) The Company recorded a $5.8 million charge in 2018 that is included in depreciable real estate reserves and impairment in the consolidated statement of operations. (8) In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. At that time, the sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. See Note 6, "Investments in Unconsolidated Joint Ventures." (9) In April 2017, we closed on the sale of a 90% interest in 102 Greene Street and accounted for our retained 10% interest in the property as an investment in unconsolidated joint ventures. We sold the remaining 10% interest in September 2017. See Note 6, "Investments in Unconsolidated Joint Ventures."

Debt and Preferred Equity Inv_2

Debt and Preferred Equity Investments (Tables)	12 Months Ended
	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Schedule of debt and preferred equity book balance roll forward	Below is a summary of the activity relating to our debt and preferred equity investments as of December 31, 2019 and 2018 (in thousands): December 31, 2019 December 31, 2018 Balance at beginning of year (1) $ 2,099,393 $ 2,114,041 Debt investment originations/accretion (2) 652,866 834,304 Preferred equity investment originations/accretion (2) 14,736 151,704 Redemptions/sales/syndications/amortization (3) (1,190,689 ) (994,906 ) Net change in loan loss reserves 4,000 (5,750 ) Balance at end of period (1) $ 1,580,306 $ 2,099,393 (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, but did not meet the conditions for sale accounting, are included in other assets and other liabilities on the consolidated balance sheets.
Schedule of Debt	Below is a summary of the balances relating to our debt and preferred equity investments as of December 31, 2019 (dollars in thousands): Floating Rate Fixed Rate Total Carrying Value Senior Financing Maturity Type Carrying Value Face Value Interest Rate Carrying Value Face Value Interest Rate Senior Mortgage Debt $ 341,513 $342,861 L + 2.75 - 5.50% $ 1,010 $1,250 3.00% $ 342,523 $ — 2020-2022 Junior Mortgage Debt 31,960 32,000 L + 6.00 - 7.25% — — — $ 31,960 100,000 2020-2021 Mezzanine Debt 245,412 247,385 L + 4.60 - 12.36% 721,175 728,138 2.90 - 10.00% $ 966,587 5,188,939 2020-2029 Preferred Equity — — — 239,236 244,983 7.00 - 11.00% $ 239,236 272,000 2020-2023 Balance at end of period $ 618,885 $ 622,246 — $ 961,421 $ 974,371 — $ 1,580,306 $ 5,560,939 —
Allowance for credit losses on financing receivables	The following table is a rollforward of our total loan loss reserves at December 31, 2019 , 2018 and 2017 (in thousands): December 31, 2019 2018 2017 Balance at beginning of year $ 5,750 $ — $ — Expensed — 6,839 — Recoveries — — — Charge-offs and reclassifications (4,000 ) (1,089 ) — Balance at end of period $ 1,750 $ 5,750 $ —
Summary of debt investments	As of December 31, 2019 and 2018 , we held the following debt investments with an aggregate weighted average current yield of 8.42% , at December 31, 2019 (in thousands): Loan Type December 31, 2019 Future Funding Obligations December 31, 2019 Senior Financing December 31, 2019 Carrying Value (1) December 31, 2018 Carrying Value (1) Maturity Date (2) Fixed Rate Investments: Mezzanine Loan (3a) $ — $ 1,160,000 $ 222,775 $ 213,185 March 2020 Mezzanine Loan — 15,000 3,500 3,500 September 2021 Mezzanine Loan — 147,000 24,952 24,932 April 2022 Mezzanine Loan — 280,000 38,734 36,585 August 2022 Mezzanine Loan — 326,574 215,737 — June 2023 Mezzanine Loan — 83,790 12,714 12,706 November 2023 Mezzanine Loan — 180,000 30,000 30,000 December 2023 Mezzanine Loan (3b) — 115,000 12,950 12,941 June 2024 Mezzanine Loan — 95,000 30,000 30,000 January 2025 Mezzanine Loan — 1,712,750 55,250 55,250 June 2027 Mezzanine Loan — — — 11,000 Total fixed rate $ — $ 4,115,114 $ 646,612 $ 430,099 Floating Rate Investments: Mortgage/Mezzanine Loan (4) $ 2,509 $ 29,420 $ 82,696 $ 62,493 January 2020 Mortgage/Mezzanine Loan — — 69,839 — March 2020 Junior Mortgage Loan — 40,000 20,000 19,986 April 2020 Mezzanine Loan 4,831 47,302 15,743 12,627 July 2020 Mortgage/Mezzanine Loan — — 19,971 19,999 August 2020 Mortgage Loan 44,737 — 106,473 88,501 September 2020 Mortgage/Mezzanine Loan — 63,990 55,573 83,449 October 2020 Mezzanine Loan 19,212 421,938 51,387 88,817 December 2021 Mortgage/Mezzanine Loan — — 35,386 35,266 December 2020 Mortgage/Mezzanine Loan (3c) 10,384 — 96,570 277,694 April 2021 Mezzanine Loan — 275,000 49,809 24,961 April 2021 Junior Mortgage Participation/Mezzanine Loan — 60,000 15,698 15,665 July 2021 Mezzanine Loan 12,999 151,175 41,395 — July 2021 Mezzanine Loan 44,000 — 13,918 — December 2022 Mezzanine Loan — 85,000 20,000 — December 2029 Mezzanine Loan — — — 53,402 Mezzanine Loan — — — 79,164 Mezzanine Loan — — — 15,333 Loan Type December 31, 2019 Future Funding Obligations December 31, 2019 Senior Financing December 31, 2019 Carrying Value (1) December 31, 2018 Carrying Value (1) Maturity Date (2) Mezzanine Loan — — — 14,822 Mortgage/Mezzanine Loan — — — 154,070 Mezzanine Loan — — — 34,886 Mortgage/Junior Mortgage Participation Loan — — — 84,012 Mortgage/Mezzanine Loan — — — 37,094 Mortgage/Mezzanine Loan — — — 98,804 Mezzanine Loan — — — 7,305 Mezzanine Loan — — — 14,998 Mezzanine Loan — — — 21,990 Mezzanine Loan (5) — — — 37,499 Total floating rate $ 138,672 $ 1,173,825 $ 694,458 $ 1,382,837 Total $ 138,672 $ 5,288,939 $ 1,341,070 $ 1,812,936 (1) Carrying value is net of discounts, premiums, original issue discounts and deferred origination fees. (2) Represents contractual maturity, excluding any unexercised extension options. (3) Carrying value is net of the following amounts that were sold or syndicated, which are included in other assets and other liabilities on the consolidated balance sheets as a result of the transfers not meeting the conditions for sale accounting: (a) $1.3 million , (b) $12.0 million and (c) $96.4 million (4) This loan was extended in January 2020. (5) In 2019, the Company accepted an assignment of the equity interests in the property in-lieu of repayment and marked the assets received and liabilities assumed to fair value.
Summary of preferred equity investments	As of December 31, 2019 and 2018 , we held the following preferred equity investments with an aggregate weighted average current yield of 9.63% at December 31, 2019 (in thousands): Type December 31, 2019 Future Funding Obligations December 31, 2019 December 31, 2019 (1) December 31, 2018 (1) Mandatory Redemption (2) Preferred Equity $ — $ 272,000 $ 141,171 $ 143,183 April 2021 Preferred Equity — 1,763,529 98,065 143,274 June 2022 Total $ — $ 2,035,529 $ 239,236 $ 286,457 (1) Carrying value is net of deferred origination fees. (2) Represents contractual maturity, excluding any unexercised extension options.

Investments in Unconsolidated_2

Investments in Unconsolidated Joint Ventures (Tables)	12 Months Ended
	Dec. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Schedule of general information on joint ventures	The following table summarizes the investments in unconsolidated joint ventures sold during the years ended December 31, 2019 , 2018 , and 2017 : Property Ownership Interest Sold Disposition Date Gross Asset Valuation (in thousands) (1) Gain (Loss) on Sale (in thousands) (2) 21 East 66th Street (3) 1 residential unit December 2019 $ 2,900 $ 279 521 Fifth Avenue 50.50% May 2019 381,000 57,874 131-137 Spring Street 20.00% January 2019 216,000 17,660 Stonehenge Portfolio (partial) Various Various - 2019 468,800 (2,408 ) 3 Columbus Circle 48.90% November 2018 851,000 160,368 Mezzanine Loan (4) 33.33% August 2018 15,000 N/A 724 Fifth Avenue 49.90% July 2018 365,000 64,587 Jericho Plaza 11.67% June 2018 117,400 147 1745 Broadway 56.87% May 2018 633,000 52,038 175-225 Third Street Brooklyn, New York 95.00% April 2018 115,000 19,483 1515 Broadway (5) 13.00% February 2018 1,950,000 — Stonehenge Portfolio (partial) Various Various - 2018 331,100 (6,063 ) 102 Greene Street 10.00% September 2017 43,500 283 76 11th Avenue (6) 33.33% May 2017 138,240 N/A Stonehenge Portfolio (partial) Various March 2017 300,000 871 (1) Represents implied gross valuation for the joint venture or sales price of the property. (2) Represents the Company's share of the gain or (loss). The gain on sale is net of $4.0 million , $11.7 million , and $0 of employee compensation accrued in connection with the realization of these investment gains in the years ended December 31, 2019 , 2018 , and 2017 , respectively. Additionally, gain (loss) amounts do not include adjustments for expenses recorded in subsequent periods. (3) We, together with our joint venture partner, closed on the sale of one residential unit at the property. (4) Our investment in a joint venture that owned a mezzanine loan secured by a commercial property in midtown Manhattan was repaid after the joint venture received repayment of the underlying loan. (5) Our investment in 1515 Broadway was marked to fair value on January 1, 2018 upon adoption of ASC 610-20. (6) Our investment in a joint venture that owned two mezzanine notes secured by interests in the entity that owns 76 11th Avenue was repaid after the joint venture received repayment of the underlying loans. December 31, 2019 and 2018 , the carrying value for acquisition, development and construction arrangements were as follows (dollars in thousands): Loan Type December 31, 2019 December 31, 2018 Maturity Date Mezzanine Loan $ — 44,357 $ — $ 44,357 The table below provides general information on each of our joint ventures as of December 31, 2019 : Property Partner Ownership Interest (1) Economic Interest (1) Unaudited Approximate Square Feet 100 Park Avenue Prudential Real Estate Investors 49.90% 49.90% 834,000 717 Fifth Avenue Jeff Sutton/Private Investor 10.92% 10.92% 119,500 800 Third Avenue Private Investors 60.52% 60.52% 526,000 919 Third Avenue (2) New York State Teacher's Retirement System 51.00% 51.00% 1,454,000 11 West 34th Street Private Investor/Jeff Sutton 30.00% 30.00% 17,150 280 Park Avenue Vornado Realty Trust 50.00% 50.00% 1,219,158 1552-1560 Broadway (3) Jeff Sutton 50.00% 50.00% 57,718 10 East 53rd Street Canadian Pension Plan Investment Board 55.00% 55.00% 354,300 21 East 66th Street (4) Private Investors 32.28% 32.28% 13,069 650 Fifth Avenue (5) Jeff Sutton 50.00% 50.00% 69,214 121 Greene Street Jeff Sutton 50.00% 50.00% 7,131 55 West 46th Street Prudential Real Estate Investors 25.00% 25.00% 347,000 Stonehenge Portfolio (6) Various Various Various 1,439,016 605 West 42nd Street The Moinian Group 20.00% 20.00% 927,358 11 Madison Avenue PGIM Real Estate 60.00% 60.00% 2,314,000 333 East 22nd Street Private Investors 33.33% 33.33% 26,926 400 East 57th Street (7) BlackRock, Inc and Stonehenge Partners 51.00% 41.00% 290,482 One Vanderbilt National Pension Service of Korea/Hines Interest LP 71.01% 71.01% — Worldwide Plaza RXR Realty / New York REIT / Private Investor 24.35% 24.35% 2,048,725 1515 Broadway Allianz Real Estate of America 56.87% 56.87% 1,750,000 2 Herald Square Israeli Institutional Investor 51.00% 51.00% 369,000 115 Spring Street Private Investor 51.00% 51.00% 5,218 (1) Ownership interest and economic interest represent the Company's interests in the joint venture as of December 31, 2019 . Changes in ownership or economic interests within the current year are disclosed in the notes below. (2) 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. We recorded our 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 joint venture. (3) The acquisition 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. (4) We hold a 32.28% interest in three retail and one residential units at the property and a 16.14% interest in three residential units at the property. (5) 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. (6) We, together with our joint venture partner, closed on the sale of one property from the Stonehenge Portfolio in February 2019 and another property in May 2019. These sales are further described under Sale of Joint Venture Interest of Properties below. (7) In October 2016, we sold a 49% interest in this property. Our 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. Our joint venture with Stonehenge remains consolidated resulting in the combined 51% interest being shown within investments in unconsolidated joint ventures on our balance sheet.
Schedule of first mortgage notes payable collateralized by the respective joint venture properties and assignment of leases	The mortgage notes and other loans payable collateralized by the respective joint venture properties and assignment of leases at December 31, 2019 and 2018 , respectively, are as follows (dollars in thousands): Property Economic Interest (1) Maturity Date Interest Rate (2) December 31, 2019 December 31, 2018 Fixed Rate Debt: 717 Fifth Avenue (mortgage) 10.92 % July 2022 4.45% $ 300,000 $ 300,000 717 Fifth Avenue (mezzanine) 10.92 % July 2022 5.50% 355,328 355,328 650 Fifth Avenue (mortgage) 50.00 % October 2022 4.46% 210,000 210,000 650 Fifth Avenue (mezzanine) 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% 500,000 500,000 1515 Broadway 56.87 % March 2025 3.93% 838,546 855,876 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% 97,735 99,828 Worldwide Plaza 24.35 % November 2027 3.98% 1,200,000 1,200,000 Stonehenge Portfolio (3) Various Various 3.50% 196,112 321,076 521 Fifth Avenue (4) — 170,000 Total fixed rate debt $ 5,351,721 $ 5,666,108 Floating Rate Debt: 10 East 53rd Street (5) 55.00 % February 2020 L+ 2.25% $ 170,000 $ 170,000 280 Park Avenue 50.00 % September 2020 L+ 1.73% 1,200,000 1,200,000 1552 Broadway 50.00 % October 2020 L+ 2.65% 195,000 195,000 121 Greene Street 50.00 % November 2020 L+ 1.50% 15,000 15,000 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% 356,972 360,000 One Vanderbilt (6) 71.01 % September 2021 L+ 2.50% 732,928 375,000 2 Herald Square 51.00 % November 2021 L+ 1.45% 190,000 133,565 55 West 46th Street (7) 25.00 % August 2022 L+ 1.25% 192,524 185,569 115 Spring Street 51.00 % September 2023 L+ 3.40% 65,550 — 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% 712 1,571 131-137 Spring Street (8) — 141,000 103 East 86th Street (9) — 38,000 Total floating rate debt $ 3,691,686 $ 3,387,705 Total joint venture mortgages and other loans payable $ 9,043,407 $ 9,053,813 Deferred financing costs, net (91,538 ) (103,191 ) Total joint venture mortgages and other loans payable, net $ 8,951,869 $ 8,950,622 (1) Economic interest represents the Company's interests in the joint venture as of December 31, 2019 . 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 December 31, 2019 , 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) Amount is comprised of $132.6 million and $63.5 million in fixed-rate mortgages that mature in April 2028 and July 2029, respectively. (4) In May 2019, we, together with our joint venture partner, closed on the sale of the property. (5) This loan was refinanced in February 2020. (6) This loan is a $1.75 billion construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial five year term with two one year extension options. Advances under the loan are subject to incurred costs, funded equity, loan to value thresholds, and entering into construction contracts. (7) In August 2019, this loan was refinanced with a new $192.5 million mortgage loan. This loan has a committed amount of $198.0 million, of which $5.5 million was unfunded as of December 31, 2019. (8) In January 2019, we closed on the sale of our interest in the property. (9) In February 2019, we, together with our joint venture partner, closed on the sale of the property.
Schedule of combined balance sheets for the unconsolidated joint ventures	The combined balance sheets for the unconsolidated joint ventures, at December 31, 2019 and 2018 , are as follows (unaudited, in thousands): December 31, 2019 December 31, 2018 Assets (1) Commercial real estate property, net $ 14,349,628 $ 14,347,673 Cash and restricted cash 336,189 381,301 Tenant and other receivables and deferred rents receivable 371,065 273,141 Debt and preferred equity investments, net — 44,357 Other assets 2,039,429 2,187,166 Total assets $ 17,096,311 $ 17,233,638 Liabilities and equity (1) Mortgages and other loans payable, net $ 8,951,869 $ 8,950,622 Deferred revenue/gain 1,501,616 1,660,838 Lease liabilities 897,380 637,168 Other liabilities 308,304 309,145 Equity 5,437,142 5,675,865 Total liabilities and equity $ 17,096,311 $ 17,233,638 Company's investments in unconsolidated joint ventures $ 2,912,842 $ 3,019,020 (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. In addition, at December 31, 2019, $133.1 million of net unamortized basis differences between the amount at which our investments are carried and our share of equity in net assets of the underlying property will be amortized through equity in net income (loss) from unconsolidated joint ventures over the remaining life of the underlying items having given rise to the differences.
Schedule of combined statements of income for the unconsolidated joint ventures	The combined statements of operations for the unconsolidated joint ventures, from acquisition date through the years ended December 31, 2019 , 2018 , and 2017 are as follows (unaudited, in thousands): Year Ended December 31, 2019 2018 2017 Total revenues $ 1,163,534 $ 1,244,804 $ 904,230 Operating expenses 202,881 219,440 157,610 Real estate taxes 212,355 226,961 142,774 Operating lease rent 24,816 18,697 16,794 Interest expense, net of interest income 372,408 363,055 250,063 Amortization of deferred financing costs 19,336 21,634 23,026 Transaction related costs — — 146 Depreciation and amortization 407,697 421,458 279,419 Total expenses $ 1,239,493 $ 1,271,245 $ 869,832 Loss on early extinguishment of debt (1,031 ) — (7,899 ) Net (loss) income before gain on sale (1) $ (76,990 ) $ (26,441 ) $ 26,499 Company's equity in net (loss) income from unconsolidated joint ventures (1) $ (34,518 ) $ 7,311 $ 21,892 (1) The combined statements of operations and the Company's equity in net income (loss) 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 (Tables)

Deferred Costs (Tables)	12 Months Ended
	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Deferred Costs	Deferred costs at December 31, 2019 and 2018 consisted of the following (in thousands): December 31, 2019 2018 Deferred leasing costs $ 466,136 $ 453,833 Less: accumulated amortization (260,853 ) (244,723 ) Deferred costs, net $ 205,283 $ 209,110

Mortgages and Other Loans Pay_2

Mortgages and Other Loans Payable (Tables)	12 Months Ended
	Dec. 31, 2019
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 December 31, 2019 and 2018 , respectively, were as follows (dollars in thousands): Property Maturity Date Interest Rate (1) December 31, 2019 December 31, 2018 Fixed Rate Debt: 762 Madison Avenue February 2022 5.00% $ 771 $ 771 100 Church Street July 2022 4.68% 209,296 213,208 420 Lexington Avenue October 2024 3.99% 299,165 300,000 400 East 58th Street (2) November 2026 3.00% 39,094 39,931 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 3.59% 35,123 35,807 315 West 33rd Street February 2027 4.17% 250,000 250,000 Total fixed rate debt $ 1,383,449 $ 1,389,717 Floating Rate Debt: FHLB Facility (4) January 2020 L+ 0.26% $ 10,000 $ — FHLB Facility (5) February 2020 L+ 0.32% 15,000 — FHLB Facility June 2020 L+ 0.17% 14,500 — 2017 Master Repurchase Agreement June 2020 L+ 2.19% 152,684 300,000 133 Greene Street August 2020 L+ 2.00% 15,523 15,523 106 Spring Street January 2021 L+ 2.50% 38,025 — 609 Fifth Avenue March 2021 L+ 2.40% 53,773 — 185 Broadway (6) November 2021 L+ 2.85% 120,110 111,869 712 Madison Avenue December 2021 L+ 1.85% 28,000 28,000 410 Tenth Avenue (7) May 2022 L+ 2.23% 330,819 — 719 Seventh Avenue September 2023 L+ 1.20% 50,000 50,000 FHLB Facility (8) — 13,000 115 Spring Street (9) — 65,550 FHLB Facility (10) — 14,500 Total floating rate debt $ 828,434 $ 598,442 Total mortgages and other loans payable $ 2,211,883 $ 1,988,159 Deferred financing costs, net of amortization (28,630 ) (26,919 ) Total mortgages and other loans payable, net $ 2,183,253 $ 1,961,240 (1) Interest rate as of December 31, 2019 , 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 $34.2 million mortgage loan and $0.9 million mezzanine 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) In January 2020, the loan was repaid and a new advance was drawn in the amount of $10.0 million with a spread of 16.5 basis points. (5) In February 2020, the loan was repaid and a new advance was drawn in the amount of $15.0 million with a spread of 26.0 basis points. (6) This loan is a $225.0 million construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial three year term with two one year extension options. Advances under the loan are subject to incurred costs and funded equity requirements. (7) This loan is a $465.0 million construction facility, with reductions in interest cost based on meeting certain conditions, and has an initial three year term with two one year extension options. Advances under the loan are subject to incurred costs and funded equity requirements. (8) In August 2019, the loan was repaid. (9) In August 2019, the Company sold a 49% interest in the property to a private investor. The transaction resulted in the deconsolidation of our remaining 51% interest. See Note 6, "Investments in Unconsolidated Joint Ventures." (10) In December 2019, the loan was repaid.

Corporate Indebtedness (Tables)

Corporate Indebtedness (Tables)	12 Months Ended
	Dec. 31, 2019
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 December 31, 2019 and 2018 , respectively, by scheduled maturity date (dollars in thousands): Issuance December 31, 2019 Unpaid Principal Balance December 31, 2019 Accreted Balance December 31, 2018 Accreted Balance Interest Rate (1) Initial Term (in Years) Maturity Date March 16, 2010 (2) $ 250,000 $ 250,000 $ 250,000 7.75 % 10 March 2020 August 7, 2018 (3) (4) 350,000 350,000 350,000 L+ 0.98 % 3 August 2021 October 5, 2017 (3) 500,000 499,695 499,591 3.25 % 5 October 2022 November 15, 2012 (5) 300,000 303,142 304,168 4.50 % 10 December 2022 December 17, 2015 (2) 100,000 100,000 100,000 4.27 % 10 December 2025 $ 1,500,000 $ 1,502,837 $ 1,503,759 Deferred financing costs, net (5,990 ) (8,545 ) $ 1,500,000 $ 1,496,847 $ 1,495,214 (1) Interest rate as of December 31, 2019 , taking into account interest rate hedges in effect during the period. Floating rate notes are presented with the stated spread over 3-month LIBOR, unless otherwise specified. (2) Issued by the Company and the Operating Partnership as co-obligors. (3) Issued by the Operating Partnership with the Company as the guarantor. (4) Beginning on August 8, 2019 and at any time thereafter, the notes are subject to redemption at the Company's option, in whole but not in part, at a redemption price equal to 100% of the principal amount of the notes, plus unpaid accrued interest thereon to the redemption date. (5) In October 2017, the Company and the Operating Partnership as co-obligors issued an additional $100.0 million of 4.50% senior unsecured notes due December 2022. The notes were priced at 105.334% of par.
Schedule of combined aggregate principal maturities	Combined aggregate principal maturities of mortgages and other loans payable, 2017 credit facility, trust preferred securities, senior unsecured notes and our share of joint venture debt as of December 31, 2019 , including as-of-right extension options and put options, were as follows (dollars in thousands): Scheduled Amortization Principal Revolving Credit Facility Unsecured Term Loans Trust Preferred Securities Senior Unsecured Notes Total Joint Venture Debt 2020 $ 11,118 $ 207,706 $ — $ — $ — $ 250,000 $ 468,824 $ 811,628 2021 11,638 239,908 — — — 350,000 601,546 805,276 2022 9,430 529,375 — — — 800,000 1,338,805 268,952 2023 7,301 50,000 240,000 1,300,000 — — 1,597,301 311,436 2024 6,032 272,749 — 200,000 — — 478,781 17,022 Thereafter 3,258 863,368 — — 100,000 100,000 1,066,626 1,813,821 $ 48,777 $ 2,163,106 $ 240,000 $ 1,500,000 $ 100,000 $ 1,500,000 $ 5,551,883 $ 4,028,135
Schedule of consolidated interest expense, excluding capitalized interest	Consolidated interest expense, excluding capitalized interest, was comprised of the following (dollars in thousands): Year Ended December 31, 2019 2018 2017 Interest expense before capitalized interest $ 246,848 $ 236,719 $ 281,551 Interest on financing leases 3,243 8,069 3,098 Interest capitalized (55,446 ) (34,162 ) (26,020 ) Interest income (4,124 ) (1,957 ) (1,584 ) Interest expense, net $ 190,521 $ 208,669 $ 257,045

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Schedule of amounts due from/to related parties	Amounts due from joint ventures and related parties at December 31, 2019 and 2018 consisted of the following (in thousands): December 31, 2019 2018 Due from joint ventures $ 9,352 $ 18,655 Other 11,769 9,378 Related party receivables $ 21,121 $ 28,033

Noncontrolling Interests on t_2

Noncontrolling Interests on the Company's Consolidated Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2019
Noncontrolling Interest [Abstract]
Schedule of Noncontrolling Interest	Below is a summary of the activity relating to the noncontrolling interests in the Operating Partnership as of December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Balance at beginning of period $ 387,805 $ 461,954 Distributions (14,729 ) (15,000 ) Issuance of common units 19,403 23,655 Redemption of common units (27,962 ) (60,718 ) Net income 13,301 12,216 Accumulated other comprehensive income allocation (2,276 ) (66 ) Fair value adjustment 34,320 (34,236 ) Balance at end of period $ 409,862 $ 387,805
Schedule of Preferred Unit Activity	Below is a summary of the preferred units of limited partnership interest in the Operating Partnership as of December 31, 2019 : Issuance Number of Units Authorized Number of Units Issued Dividends Per Unit (1) Liquidation Preference Per Unit (2) Conversion Price Per Unit (3) Date of Issuance 4.50% Series G (4) 1,902,000 1,902,000 $ 1.1250 $ 25.00 $ 88.50 January 2012 7.00% Series F 60 60 $ 70.0000 $ 1,000.00 $ 29.12 January 2007 3.50% Series K 700,000 563,954 $ 0.8750 $ 25.00 $ 134.67 August 2014 4.00% Series L 500,000 378,634 $ 1.0000 $ 25.00 — August 2014 3.75% Series M 1,600,000 1,600,000 $ 0.9375 $ 25.00 — February 2015 3.00% Series N (5) 552,303 552,303 $ 0.7500 $ 25.00 — June 2015 Series O (6) 1 1 (6 ) (6 ) — June 2015 4.00% Series P 200,000 200,000 $ 1.0000 $ 25.00 — July 2015 3.50% Series Q 268,000 268,000 $ 0.8750 $ 25.00 $ 148.95 July 2015 3.50% Series R 400,000 400,000 $ 0.8750 $ 25.00 $ 154.89 August 2015 4.00% Series S 1,077,280 1,077,280 $ 1.0000 $ 25.00 — August 2015 2.75% Series T 230,000 230,000 $ 0.6875 $ 25.00 $ 119.02 March 2016 4.50% Series U (7) 680,000 680,000 $ 1.1250 $ 25.00 — March 2016 3.50% Series A (8) 109,161 109,161 $ 35.0000 $ 1,000.00 — August 2015 3.50% Series V 40,000 40,000 $ 0.8750 $ 25.00 — May 2019 (1) Dividends are cumulative, subject to certain provisions. (2) Units are redeemable at any time at par for cash at the option of the unitholder unless otherwise specified. (3) If applicable, 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) the amount shown in the table. (4) Common units of limited partnership interest in the Operating Partnership issued in a conversion 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. (5) All of the outstanding units were redeemed at par for cash by the unitholder during the twelve months ended December 31, 2019 . (6) The holder of the Series O preferred unit is entitled to quarterly dividends in an amount calculated as (i) 1,350 multiplied by (ii) the current distribution per common unit of limited partnership in SL Green Operating Partnership. The holder has the right to require the Operating Partnership to repurchase the Series O unit for cash at a price that is determined based on the closing price of the Company's common stock at the time such right is exercised. The unit's liquidation preference is the fair market value of the unit at the time of a liquidation event. (7) The annual dividend is subject to reduction upon the occurrence of certain circumstances. The minimum annual dividend is $0.75 per unit. (8) Issued through a consolidated subsidiary. The units are convertible on a one-for-one basis, into the Series B Preferred Units of limited partnership interest, or the Subsidiary Series B Preferred Units. The Subsidiary Series B Preferred Units can be converted at any time, at the option of the unitholder, into a number of common stock equal to 6.71348 shares of common stock for each Subsidiary Series B Preferred Unit. As of December 31, 2019 , no Subsidiary Series B Preferred Units have been issued. Below is a summary of the activity relating to the preferred units in the Operating Partnership as of December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Balance at beginning of period $ 300,427 $ 301,735 Issuance of preferred units 1,000 — Redemption of preferred units (18,142 ) (1,308 ) Balance at end of period $ 283,285 $ 300,427

Stockholders' Equity of the C_2

Stockholders' Equity of the Company (Tables)	12 Months Ended
	Dec. 31, 2019
Stockholders' Equity Note [Abstract]
Class of Treasury Stock	At December 31, 2019 repurchases executed under the program were as follows: Period Shares repurchased Average price paid per share Cumulative number of shares repurchased as part of the repurchase plan or programs Year ended 2017 8,342,411 $101.64 8,342,411 Year ended 2018 9,744,911 $96.22 18,087,322 Year ended 2019 4,596,171 $83.62 22,683,493
Schedule of Common Stock Issued and Proceeds Received Dividend Reinvestments	The following table summarizes SL Green common stock issued, and proceeds received from dividend reinvestments and/or stock purchases under the DRSPP for the years ended December 31, 2019 , 2018 , and 2017 , respectively (dollars in thousands): Year Ended December 31, 2019 2018 2017 Shares of common stock issued 3,867 1,399 2,141 Dividend reinvestments/stock purchases under the DRSPP $ 334 $ 136 $ 223
Schedule of Earnings Per Share	SL Green's earnings per share for the years ended December 31, 2019 , 2018 , and 2017 are computed as follows (in thousands): Year Ended December 31, Numerator 2019 2018 2017 Basic Earnings: Income attributable to SL Green common stockholders $ 255,484 $ 232,312 $ 86,424 Less: distributed earnings allocated to participating securities (1,739 ) $ (552 ) $ (471 ) Net income attributable to SL Green common stockholders (numerator for basic earnings per share) $ 253,745 $ 231,760 $ 85,953 Add back: Dilutive effect of earnings allocated to participating securities 1,719 552 471 Add back: Effect of dilutive securities (redemption of units to common shares) 13,301 12,216 3,995 Income attributable to SL Green common stockholders (numerator for diluted earnings per share) $ 268,765 $ 244,528 $ 90,419 Year Ended December 31, Denominator 2019 2018 2017 Basic Shares: Weighted average common stock outstanding 81,733 86,753 98,571 Effect of Dilutive Securities: Operating Partnership units redeemable for common shares 4,275 4,562 4,556 Stock-based compensation plans 554 215 276 Diluted weighted average common stock outstanding 86,562 91,530 103,403

Partners' Capital of the Oper_2

Partners' Capital of the Operating Partnership (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Schedule of Calculation of Numerator and Denominator in Earnings Per Unit	The Operating Partnership's earnings per unit for the years ended December 31, 2019 , 2018 , and 2017 respectively are computed as follows (in thousands): Year Ended December 31, Numerator 2019 2018 2017 Basic Earnings: Income attributable to SLGOP common unitholders $ 268,785 $ 244,528 $ 90,419 Less: distributed earnings allocated to participating securities (1,739 ) $ (552 ) $ (471 ) Net Income attributable to SLGOP common unitholders (numerator for basic earnings per unit) $ 267,046 $ 243,976 $ 89,948 Add back: Dilutive effect of earnings allocated to participating securities 1,719 552 471 Income attributable to SLGOP common unitholders $ 268,765 $ 244,528 $ 90,419 Year Ended December 31, Denominator 2019 2018 2017 Basic units: Weighted average common units outstanding 86,008 91,315 103,127 Effect of Dilutive Securities: Stock-based compensation plans 554 215 276 Diluted weighted average common units outstanding 86,562 91,530 103,403

Share-based Compensation (Table

Share-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Schedule of weighted average assumptions used to estimate the grant date fair value of options granted	The fair value of each stock option or LTIP Unit granted is estimated on the date of grant using the Black-Scholes option pricing model based on historical information with the following weighted average assumptions for grants during the years ended December 31, 2018 and 2017 . There were no grants during the year ended December 31, 2019 . 2019 2018 2017 Dividend yield none 2.85 % 2.51 % Expected life zero years 3.5 years 4.4 years Risk-free interest rate none 2.48 % 1.73 % Expected stock price volatility none 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 December 31, 2019 , 2018 , and 2017 and changes during the years ended December 31, 2019 , 2018 , and 2017 are as follows: 2019 2018 2017 Options Outstanding Weighted Average Exercise Price Options Outstanding Weighted Average Exercise Price Options Weighted Balance at beginning of year $ 1,137,017 $ 103.54 $ 1,548,719 $ 101.48 $ 1,737,213 $ 98.44 Granted — — 6,000 97.91 174,000 105.66 Exercised — — (316,302 ) 90.22 (292,193 ) 81.07 Lapsed or canceled (99,949 ) 115.81 (101,400 ) 113.22 (70,301 ) 121.68 Balance at end of year $ 1,037,068 $ 102.36 $ 1,137,017 $ 103.54 $ 1,548,719 $ 101.48 Options exercisable at end of year 914,929 $ 101.69 783,035 $ 101.28 800,902 $ 94.33 Weighted average fair value of options granted during the year $ — $ 84,068 $ 3,816,652
Schedule of other share-based compensation, activity	A summary of the Company's restricted stock as of December 31, 2019 , 2018 , and 2017 and charges during the years ended December 31, 2019 , 2018 , and 2017 are as follows: 2019 2018 2017 Balance at beginning of year 3,452,016 3,298,216 3,202,031 Granted 126,350 162,900 96,185 Canceled (11,900 ) (9,100 ) — Balance at end of year 3,566,466 3,452,016 3,298,216 Vested during the year 113,259 92,114 95,736 Compensation expense recorded $ 12,892,249 $ 12,757,704 $ 9,809,749 Total fair value of restricted stock granted during the year $ 11,131,181 $ 13,440,503 $ 9,905,986

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income	The following tables set forth the changes in accumulated other comprehensive (loss) income by component as of December 31, 2019 , 2018 and 2017 (in thousands): Net unrealized gain (loss) on derivative instruments ( 1 ) SL Green’s share of joint venture net unrealized gain (loss) on derivative instruments ( 2 ) Net unrealized gain on marketable securities Total Balance at December 31, 2016 $ 12,596 $ 4,021 $ 5,520 $ 22,137 Other comprehensive (loss) income before reclassifications (1,618 ) 233 (1,348 ) (2,733 ) Amounts reclassified from accumulated other comprehensive income 1,564 766 (3,130 ) (800 ) Balance at December 31, 2017 12,542 5,020 1,042 18,604 Other comprehensive (loss) income before reclassifications (2,252 ) (103 ) 51 (2,304 ) Amounts reclassified from accumulated other comprehensive income (574 ) (618 ) — (1,192 ) Balance at December 31, 2018 9,716 4,299 1,093 15,108 Other comprehensive (loss) income before reclassifications (32,723 ) (11,956 ) 1,184 (43,495 ) Amounts reclassified from accumulated other comprehensive loss 227 (325 ) — (98 ) Balance at December 31, 2019 $ (22,780 ) $ (7,982 ) $ 2,277 $ (28,485 ) (1) Amount reclassified from accumulated other comprehensive (loss) income is included in interest expense in the respective consolidated statements of operations. As of December 31, 2019 and 2018 , the deferred net (gains) losses from these terminated hedges, which is included in accumulated other comprehensive loss relating to net unrealized gain (loss) on derivative instrument, was $(0.7) million and $1.3 million , respectively. (2) Amount reclassified from accumulated other comprehensive (loss) income is included in equity in net (loss) income from unconsolidated joint ventures in the respective consolidated statements of operations.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements, Recurring and Nonrecurring	The following tables set forth the assets and liabilities that we measure at fair value on a recurring and non-recurring basis by their levels in the fair value hierarchy at December 31, 2019 and 2018 (in thousands): December 31, 2019 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 29,887 $ — $ 29,887 $ — Interest rate cap and swap agreements (included in other assets) $ 4,419 $ — $ 4,419 $ — Liabilities: Interest rate cap and swap agreements (included in other liabilities) $ 29,110 $ — $ 29,110 $ — December 31, 2018 Total Level 1 Level 2 Level 3 Assets: Marketable securities $ 28,638 $ — $ 28,638 $ — Interest rate cap and swap agreements (included in other assets) $ 18,676 $ — $ 18,676 $ — Liabilities: Interest rate cap and swap agreements (included in other liabilities) $ 7,663 $ — $ 7,663 $ —
Fair Value, by Balance Sheet Grouping	The following table provides the carrying value and fair value of these financial instruments as of December 31, 2019 and December 31, 2018 (in thousands): December 31, 2019 December 31, 2018 Carrying Value (1) Fair Value Carrying Value (1) Fair Value Debt and preferred equity investments $ 1,580,306 (2) $ 2,099,393 (2) Fixed rate debt $ 3,536,286 $ 3,642,770 $ 3,543,476 $ 3,230,127 Variable rate debt 2,018,434 2,018,714 2,048,442 2,057,966 $ 5,554,720 $ 5,661,484 $ 5,591,918 $ 5,288,093 (1) Amounts exclude net deferred financing costs. (2) At December 31, 2019 , debt and preferred equity investments had an estimated fair value ranging between $1.6 billion and $1.7 billion . At December 31, 2018 , debt and preferred equity investments had an estimated fair value ranging between $2.1 billion and $2.3 billion .

Financial Instruments_ Deriva_2

Financial Instruments: Derivatives and Hedging (Tables)	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of notional and fair value of derivative financial instruments and foreign currency hedges	The following table summarizes the notional value at inception and fair value of our consolidated derivative financial instruments at December 31, 2019 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 (dollars in thousands). Notional Value Strike Rate Effective Date Expiration Date Balance Sheet Location Fair Value Interest Rate Cap $ 300,000 3.750 % May 2019 May 2020 Other Assets $ — Interest Rate Swap 100,000 1.928 % December 2017 November 2020 Other Liabilities (281 ) Interest Rate Swap 100,000 1.934 % December 2017 November 2020 Other Liabilities (286 ) Interest Rate Cap 111,869 3.500 % December 2019 December 2020 Other Assets — Interest Rate Cap 85,000 4.000 % March 2019 March 2021 Other Assets — Interest Rate Swap 200,000 1.131 % July 2016 July 2023 Other Assets 3,015 Interest Rate Swap 100,000 1.161 % July 2016 July 2023 Other Assets 1,404 Interest Rate Swap 150,000 2.696 % January 2019 January 2024 Other Liabilities (6,570 ) Interest Rate Swap 150,000 2.721 % January 2019 January 2026 Other Liabilities (9,344 ) Interest Rate Swap 200,000 2.740 % January 2019 January 2026 Other Liabilities (12,629 ) $ (24,691 )
Schedule of effect of derivative financial instruments on consolidated statements of income	The following table presents the effect of our derivative financial instruments and our share of our joint ventures' derivative financial instruments that are designated and qualify as hedging instruments on the consolidated statements of operations for the years ended December 31, 2019 , 2018 , and 2017 , respectively (in thousands): Amount of Loss Recognized in Other Comprehensive Loss Location of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income Amount of (Loss) Gain Reclassified from Accumulated Other Comprehensive Loss into Income Year Ended Year Ended Derivative 2019 2018 2017 2019 2018 2017 Interest Rate Swaps/Caps $ (33,907 ) $ (2,284 ) $ (2,282 ) Interest expense $ (261 ) $ 1,168 $ 1,816 Share of unconsolidated joint ventures' derivative instruments (10,322 ) (1,788 ) (200 ) Equity in net income from unconsolidated joint ventures 256 1,097 980 $ (44,229 ) $ (4,072 ) $ (2,482 ) $ (5 ) $ 2,265 $ 2,796

Rental Income (Tables)

Rental Income (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Lessor, Operating Lease, Payments to be Received, Maturity	Approximate future minimum rents to be received over the next five years and thereafter for non-cancelable operating leases in effect at December 31, 2019 for the consolidated properties, including consolidated joint venture properties, and our share of unconsolidated joint venture properties are as follows (in thousands): Consolidated Properties Unconsolidated Properties 2020 $ 799,001 $ 390,725 2021 651,815 397,524 2022 600,912 380,598 2023 536,835 354,621 2024 496,476 325,459 Thereafter 2,938,340 1,986,928 $ 6,023,379 $ 3,835,855
Schedule of Future Minimum Rental Payments for Operating Leases	As of December 31, 2018 , under ASC 840, approximate future minimum rents to be received over the next five years and thereafter for non-cancelable operating leases for the consolidated properties, including consolidated joint venture properties, and our share of unconsolidated joint venture properties are as follows (in thousands): Consolidated Properties Unconsolidated Properties 2019 $ 830,336 $ 348,060 2020 765,610 375,228 2021 625,956 380,886 2022 562,250 348,222 2023 500,499 333,501 Thereafter 3,272,014 2,098,995 $ 6,556,665 $ 3,884,892
Operating Lease, Lease Income	The components of lease revenues were as follows (in thousands): Twelve Months Ended December 31, 2019 Twelve Months Ended December 31, 2018 Fixed lease payments $ 858,587 $ 858,160 Variable lease payments 120,496 113,596 Total lease payments $ 979,083 $ 971,756 Amortization of acquired above and below-market leases 4,474 6,818 Total rental revenue $ 983,557 $ 978,574

Benefit Plans (Tables)

Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Schedule of Contributions made to Multi-Employer Plans	Contributions we made to the multi-employer plans for the years ended December 31, 2019 , 2018 and 2017 are included in the table below (in thousands): Benefit Plan 2019 2018 2017 Pension Plan $ 3,103 $ 3,017 $ 3,856 Health Plan 9,949 9,310 11,426 Other plans 1,108 1,106 1,463 Total plan contributions $ 14,160 $ 13,433 $ 16,745

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Schedule Of Ground Lease Arrangements	The table below summarizes our current ground lease arrangements as of December 31, 2019 : Property (1) Year of Current Expiration Year of Final Expiration (2) 1185 Avenue of the Americas 2043 2043 625 Madison Avenue 2022 2054 420 Lexington Avenue 2050 2080 711 Third Avenue (3) 2033 2083 461 Fifth Avenue (4) 2027 2084 1055 Washington Blvd, Stamford, Connecticut 2090 2090 1080 Amsterdam Avenue (5) 2111 2111 30 East 40th Street (5) 2114 2114 Other Various Various (1) All leases are classified as operating leases unless otherwise specified. (2) Reflects exercise of all available renewal options. (3) The Company owns 50% of the fee interest. (4) The Company has an option to purchase the ground lease for a fixed price on a specific date. (5) A portion of the lease is classified as a financing lease.
Finance lease, liability, maturity	The following is a schedule of future minimum lease payments under financing leases and operating leases with initial terms in excess of one year as of December 31, 2019 (in thousands): Financing leases Operating leases (1) 2020 $ 2,619 $ 31,508 2021 2,794 31,702 2022 2,794 29,548 2023 2,794 27,243 2024 2,819 27,263 Thereafter 814,283 649,289 Total minimum lease payments $ 828,103 $ 796,553 Amount representing interest (783,655 ) Amount discounted using incremental borrowing rate (414,882 ) Lease liabilities $ 44,448 $ 381,671 (1) As of December 31, 2019 , the total minimum sublease rentals to be received in the future under non-cancelable subleases is $1.6 billion .
Schedule of future minimum rental payments for opeating leases	The following is a schedule of future minimum lease payments under financing leases and operating leases with initial terms in excess of one year as of December 31, 2019 (in thousands): Financing leases Operating leases (1) 2020 $ 2,619 $ 31,508 2021 2,794 31,702 2022 2,794 29,548 2023 2,794 27,243 2024 2,819 27,263 Thereafter 814,283 649,289 Total minimum lease payments $ 828,103 $ 796,553 Amount representing interest (783,655 ) Amount discounted using incremental borrowing rate (414,882 ) Lease liabilities $ 44,448 $ 381,671 (1) As of December 31, 2019 , the total minimum sublease rentals to be received in the future under non-cancelable subleases is $1.6 billion .

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Schedule of selected results of operations and selected asset information	Selected consolidated results of operations for the years ended December 31, 2019 , 2018 , and 2017 , and selected asset information as of December 31, 2019 and 2018 , regarding our operating segments are as follows (in thousands): Real Estate Segment Debt and Preferred Equity Segment Total Company Total revenues Years ended: December 31, 2019 $ 1,043,405 $ 195,590 $ 1,238,995 December 31, 2018 1,025,900 201,492 1,227,392 December 31, 2017 1,317,602 193,871 1,511,473 Net Income Years ended: December 31, 2019 $ 158,972 $ 132,515 $ 291,487 December 31, 2018 129,253 141,603 270,856 December 31, 2017 (69,294 ) 170,363 101,069 Total assets As of: December 31, 2019 $ 11,063,155 $ 1,703,165 $ 12,766,320 December 31, 2018 10,481,594 2,269,764 12,751,358

Quarterly Financial Data of t_3

Quarterly Financial Data of the Company (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Summarized quarterly financial data for the years ended December 31, 2019 and 2018 was as follows (in thousands, except for per share amounts): 2019 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 308,082 $ 313,634 $ 313,024 $ 304,255 Total expenses (252,712 ) (263,341 ) (258,383 ) (260,328 ) Equity in net loss from unconsolidated joint ventures (11,874 ) (9,864 ) (7,546 ) (5,234 ) Equity in net gain on sale of interest in unconsolidated joint venture/real estate — — 59,015 17,166 Purchase price and other fair value adjustments — 3,799 67,631 (2,041 ) (Loss) gain on sale of real estate, net (19,241 ) 3,541 — (1,049 ) Depreciable real estate reserves and impairment — (7,047 ) — — Noncontrolling interests and preferred unit distributions (3,086 ) (3,827 ) (8,901 ) (5,239 ) Net income attributable to SL Green 21,169 36,895 164,840 47,530 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income (loss) attributable to SL Green common stockholders $ 17,432 $ 33,157 $ 161,103 $ 43,792 Net income attributable to common stockholders per common share—basic $ 0.21 $ 0.40 $ 1.94 $ 0.52 Net income attributable to common stockholders per common share—diluted $ 0.21 $ 0.40 $ 1.94 $ 0.52 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net (loss) income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 (Loss) gain on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions 838 (7,507 ) (8,606 ) (8,319 ) Net (loss) income attributable to SL Green (57,482 ) 91,947 107,293 105,504 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SL Green common stockholders $ (61,219 ) $ 88,209 $ 103,556 $ 101,766 Net (loss) income attributable to common stockholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common stockholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12

Quarterly Financial Data of t_4

Quarterly Financial Data of the Operating Partnership (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Condensed Income Statements, Captions [Line Items]
Schedule of Quarterly Financial Information	Summarized quarterly financial data for the years ended December 31, 2019 and 2018 was as follows (in thousands, except for per share amounts): 2019 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 308,082 $ 313,634 $ 313,024 $ 304,255 Total expenses (252,712 ) (263,341 ) (258,383 ) (260,328 ) Equity in net loss from unconsolidated joint ventures (11,874 ) (9,864 ) (7,546 ) (5,234 ) Equity in net gain on sale of interest in unconsolidated joint venture/real estate — — 59,015 17,166 Purchase price and other fair value adjustments — 3,799 67,631 (2,041 ) (Loss) gain on sale of real estate, net (19,241 ) 3,541 — (1,049 ) Depreciable real estate reserves and impairment — (7,047 ) — — Noncontrolling interests and preferred unit distributions (3,086 ) (3,827 ) (8,901 ) (5,239 ) Net income attributable to SL Green 21,169 36,895 164,840 47,530 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income (loss) attributable to SL Green common stockholders $ 17,432 $ 33,157 $ 161,103 $ 43,792 Net income attributable to common stockholders per common share—basic $ 0.21 $ 0.40 $ 1.94 $ 0.52 Net income attributable to common stockholders per common share—diluted $ 0.21 $ 0.40 $ 1.94 $ 0.52 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net (loss) income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 (Loss) gain on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions 838 (7,507 ) (8,606 ) (8,319 ) Net (loss) income attributable to SL Green (57,482 ) 91,947 107,293 105,504 Perpetual preferred stock dividends (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SL Green common stockholders $ (61,219 ) $ 88,209 $ 103,556 $ 101,766 Net (loss) income attributable to common stockholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common stockholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12
SL Green Operating Partnership
Condensed Income Statements, Captions [Line Items]
Schedule of Quarterly Financial Information	Summarized quarterly financial data for the years ended December 31, 2019 and 2018 was as follows (in thousands, except for per share amounts): 2019 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 308,082 $ 313,634 $ 313,024 $ 304,255 Total expenses (252,713 ) (263,341 ) (258,383 ) (260,328 ) Equity in net loss from unconsolidated joint ventures (11,874 ) (9,864 ) (7,546 ) (5,234 ) Equity in net gain on sale of interest in unconsolidated joint venture/real estate — — 59,015 17,166 Purchase price and other fair value adjustments — 3,799 67,631 (2,041 ) (Loss) gain on sale of real estate, net (19,241 ) 3,541 — (1,049 ) Depreciable real estate reserves and impairment — (7,047 ) — — Noncontrolling interests and preferred unit distributions (2,091 ) (2,108 ) (591 ) (2,961 ) Net income attributable to SLGOP 22,163 38,614 173,150 49,808 Perpetual preferred units distributions (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net income attributable to SLGOP common unitholders $ 18,426 $ 34,876 $ 169,413 $ 46,070 Net income attributable to common unitholders per common share—basic $ 0.21 $ 0.40 $ 1.94 $ 0.52 Net income attributable to common unitholders per common share—diluted $ 0.21 $ 0.40 $ 1.94 $ 0.52 2018 Quarter Ended December 31 September 30 June 30 March 31 Total revenues $ 317,036 $ 307,545 $ 301,116 $ 301,695 Total expenses (267,678 ) (265,553 ) (258,303 ) (258,282 ) Equity in net (loss) income from unconsolidated joint ventures (2,398 ) 971 4,702 4,036 Equity in net gain (loss) on sale of interest in unconsolidated joint venture/real estate 167,445 70,937 72,025 (6,440 ) Purchase price and other fair value adjustments — (3,057 ) 11,149 49,293 (Loss) gain on sale of real estate, net (36,984 ) (2,504 ) (14,790 ) 23,521 Depreciable real estate reserves and impairment (220,852 ) (6,691 ) — — Loss on early extinguishment of debt (14,889 ) (2,194 ) — — Noncontrolling interests and preferred unit distributions (2,601 ) (2,710 ) (3,020 ) (3,047 ) Net (loss) income attributable to SLGOP (60,921 ) 96,744 112,879 110,776 Perpetual preferred units distributions (3,737 ) (3,738 ) (3,737 ) (3,738 ) Net (loss) income attributable to SLGOP common unitholders $ (64,658 ) $ 93,006 $ 109,142 $ 107,038 Net (loss) income attributable to common unitholders per common share—basic $ (0.73 ) $ 1.03 $ 1.19 $ 1.12 Net (loss) income attributable to common unitholders per common share—diluted $ (0.73 ) $ 1.03 $ 1.19 $ 1.12

Organization and Basis of Pre_3

Organization and Basis of Presentation - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
SL Green Operating Partnership | Service Corporation
Organization
Percentage of ownership in SL Green Management LLC owned by operating partnership (percent)	95.00%
SL Green Operating Partnership
Organization
Noncontrolling interest in the operating partnership (as a percent)	5.03%	4.70%
SLG Management LLC | SL Green Management
Organization
Percentage of ownership in SL Green Management LLC owned by operating partnership (percent)	100.00%

Organization and Basis of Pre_4

Organization and Basis of Presentation - Schedule of Commercial Office Properties (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)ft²buildingshares	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Real estate properties
Number of Properties | building	71
Approximate Square Feet	27,607,971
Weighted Average Occupancy unaudited (as a percent)	94.30%
Debt and preferred equity investments including investments held by unconsolidated joint ventures | $	$ 1,580,306	$ 2,099,393	$ 2,114,041
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	61
Approximate Square Feet	25,499,092
Weighted Average Occupancy unaudited (as a percent)	94.20%
Residential
Real estate properties
Number of Properties | building	10
Approximate Square Feet	2,108,879
Weighted Average Occupancy unaudited (as a percent)	95.70%
Managed office properties
Real estate properties
Number of Properties | building	2
Approximate Square Feet	2,100,000
Debt and preferred equity investments including investments held by unconsolidated joint ventures | $	$ 1,700,000
Debt and preferred equity investments and other financing receivables included in other balance sheet items | $	$ 100,000
Consolidated properties
Real estate properties
Number of Properties | building	43
Approximate Square Feet	14,438,964
Consolidated properties | Commercial properties
Real estate properties
Number of Properties | building	41
Approximate Square Feet	13,993,859
Consolidated properties | Residential
Real estate properties
Number of Properties | building	2
Approximate Square Feet	445,105
Unconsolidated properties
Real estate properties
Number of Properties | building	28
Approximate Square Feet	13,169,007
Unconsolidated properties | Commercial properties
Real estate properties
Number of Properties | building	20
Approximate Square Feet	11,505,233
Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	8
Approximate Square Feet	1,663,774
Manhattan
Real estate properties
Number of Properties | building	52
Approximate Square Feet	24,402,292
Weighted Average Occupancy unaudited (as a percent)	94.60%
Manhattan | Office
Real estate properties
Number of Properties | building	30
Approximate Square Feet	23,603,274
Weighted Average Occupancy unaudited (as a percent)	94.50%
Manhattan | Retail
Real estate properties
Number of Properties | building	14
Approximate Square Feet	609,480
Weighted Average Occupancy unaudited (as a percent)	98.40%
Manhattan | Development/Redevelopment
Real estate properties
Number of Properties | building	7
Approximate Square Feet	189,538
Weighted Average Occupancy unaudited (as a percent)	84.90%
Manhattan | Fee Interest
Real estate properties
Number of Properties | building	1
Approximate Square Feet	0
Weighted Average Occupancy unaudited (as a percent)	0.00%
Manhattan | Residential
Real estate properties
Number of Properties | building	10
Approximate Square Feet	2,108,879
Weighted Average Occupancy unaudited (as a percent)	95.70%
Manhattan | Consolidated properties
Real estate properties
Number of Properties | building	32
Approximate Square Feet	12,897,059
Manhattan | Consolidated properties | Office
Real estate properties
Number of Properties | building	20
Approximate Square Feet	12,387,091
Manhattan | Consolidated properties | Retail
Real estate properties
Number of Properties | building	6
Approximate Square Feet	320,430
Manhattan | Consolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	6
Approximate Square Feet	189,538
Manhattan | Consolidated properties | Fee Interest
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0
Manhattan | Consolidated properties | Residential
Real estate properties
Number of Properties | building	2
Approximate Square Feet	445,105
Manhattan | Consolidated properties | Dual property type, retail portion
Real estate properties
Approximate Square Feet	270,132
Manhattan | Consolidated properties | Dual property type, residential portion
Real estate properties
Approximate Square Feet	222,855
Manhattan | Unconsolidated properties
Real estate properties
Number of Properties | building	20
Approximate Square Feet	11,505,233
Manhattan | Unconsolidated properties | Office
Real estate properties
Number of Properties | building	10
Approximate Square Feet	11,216,183
Manhattan | Unconsolidated properties | Retail
Real estate properties
Number of Properties | building	8
Approximate Square Feet	289,050
Manhattan | Unconsolidated properties | Development/Redevelopment
Real estate properties
Number of Properties | building	1
Approximate Square Feet	0
Manhattan | Unconsolidated properties | Fee Interest
Real estate properties
Number of Properties | building	1
Approximate Square Feet	0
Manhattan | Unconsolidated properties | Residential
Real estate properties
Number of Properties | building	8
Approximate Square Feet	1,663,774
Suburban
Real estate properties
Number of Properties | building	9
Approximate Square Feet	1,096,800
Weighted Average Occupancy unaudited (as a percent)	86.40%
Suburban | Office
Real estate properties
Number of Properties | building	8
Approximate Square Feet	1,044,800
Weighted Average Occupancy unaudited (as a percent)	85.70%
Suburban | Retail
Real estate properties
Number of Properties | building	1
Approximate Square Feet	52,000
Weighted Average Occupancy unaudited (as a percent)	100.00%
Suburban | Consolidated properties
Real estate properties
Number of Properties | building	9
Approximate Square Feet	1,096,800
Suburban | Consolidated properties | Office
Real estate properties
Number of Properties | building	8
Approximate Square Feet	1,044,800
Suburban | Consolidated properties | Retail
Real estate properties
Number of Properties | building	1
Approximate Square Feet	52,000
Suburban | Unconsolidated properties
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0
Suburban | Unconsolidated properties | Office
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0
Suburban | Unconsolidated properties | Retail
Real estate properties
Number of Properties | building	0
Approximate Square Feet	0

Organization and Basis of Pre_5

Organization and Basis of Presentation - Subsequent Event (Details) $ in Millions	Feb. 24, 2020USD ($)
315 West 33rd Street | Subsequent Event
Subsequent Event [Line Items]
Gross asset valuation of property to be sold	$ 446.5

Significant Accounting Polici_4

Significant Accounting Policies - Investments in Commercial Real Estate Properties (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Real Estate [Line Items]
Weighted average amortization period, above-market lease costs	1 year 8 months 12 days
Weighted average amortization period, below-market lease costs	2 years 9 months 18 days
Weighted average amortization period, in-place lease costs	3 years 6 months
Period from cessation of major construction activity to completion of construction project, maximum	1 year
Depreciation expense (including amortization of the capital lease asset)	$ 233,500,000	$ 242,800,000	$ 365,300,000
Amortization of above and below Market Leases	4,500,000	6,800,000	20,300,000
Reduction in interest expense from amortization of above-market rate mortgages	0	0	$ 800,000
Identified intangible assets (included in other assets):
Gross amount	255,198,000	266,540,000
Accumulated amortization	(228,223,000)	(241,040,000)
Net	26,975,000	25,500,000
Identified intangible liabilities (included in deferred revenue):
Gross amount	282,048,000	276,245,000
Accumulated amortization	(249,514,000)	(253,767,000)
Net	32,534,000	22,478,000
Net intangible assets reclassed to assets held for sale	0	0
Net intangible liabilities reclassed to liabilities relates to assets held for sale	0	$ 0
Other Identifiable Assets
Estimated annual amortization
2020	5,183,000
2021	3,638,000
2022	2,064,000
2023	1,435,000
2024	1,040,000
Acquired above-market leases, net of acquired below-market leases
Below Market Lease, Net, Amortization Income, Fiscal Year Maturity [Abstract]
2020	(4,320,000)
2021	(2,748,000)
2022	(2,224,000)
2023	(1,301,000)
2024	$ (834,000)
Minimum | Above Market Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	1 year
Minimum | Below Market Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	1 year
Minimum | In Place Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	1 year
Maximum | Above Market Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	14 years
Maximum | Below Market Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	14 years
Maximum | In Place Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	14 years
Building (fee ownership)
Real Estate [Line Items]
Estimated useful life (in years)	40 years
Building (leasehold interest) | Maximum
Real Estate [Line Items]
Estimated useful life (in years)	40 years
Right of use assets - financing leases | Maximum
Real Estate [Line Items]
Estimated useful life (in years)	40 years
Furniture and fixtures | Minimum
Real Estate [Line Items]
Estimated useful life (in years)	4 years
Furniture and fixtures | Maximum
Real Estate [Line Items]
Estimated useful life (in years)	7 years
Building | Minimum
Real Estate [Line Items]
Estimated useful life (in years)	3 years
Building | Maximum
Real Estate [Line Items]
Estimated useful life (in years)	40 years

Significant Accounting Polici_5

Significant Accounting Policies - Investment in Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Investment in Marketable Securities
Marketable Securities		$ 29,887	$ 28,638
Proceeds from sale of marketable securities	$ 55,100
Realized gain (loss) on investment in marketable securities	$ (3,300)
Fair Value
Investment in Marketable Securities
Marketable Securities		29,887	28,638
Commercial mortgage-backed securities
Investment in Marketable Securities
Marketable Securities		29,887	28,638
Cost basis of commercial mortgage backed securities		27,500	27,500
Equity marketable securities
Investment in Marketable Securities
Cost basis of commercial mortgage backed securities		$ 0	$ 0

Significant Accounting Polici_6

Significant Accounting Policies - Investments in Unconsolidated Joint Ventures/Deferred Lease Costs/Revenue Recognition/Income Taxes (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)joint_venture$ / shares	Dec. 31, 2018USD ($)$ / shares	Dec. 31, 2017USD ($)$ / shares
Schedule of Equity Method Investments [Line Items]
Number of joint ventures with performance guarantees under master leases | joint_venture	1
Deferred Lease Costs [Abstract]
Portion of compensation capitalized | $	$ 6.3	$ 15.7	$ 16.4
Estimated average lease term (in years)	8 years
Days past due for income recognition on debt and preferred equity investments to be suspended	90 days
Income taxes
Federal, state and local tax provision | $	$ 1.5	$ 2.8	$ 4.3
Dividends per share paid (in dollars per share)	$ 3.40	$ 3.25	$ 3.10
Ordinary Income Dividend
Income taxes
Dividends per share paid (in dollars per share)	2.59	1.46	1.24
Capital Gains Dividend
Income taxes
Dividends per share paid (in dollars per share)	$ 0.81	$ 1.79	$ 1.86

Significant Accounting Polici_7

Significant Accounting Policies - Concentrations of Credit Risk/Reclassification (Details)	1 Months Ended	12 Months Ended
	Jan. 31, 2020	Dec. 31, 2019Tenantagreement	Dec. 31, 2018	Dec. 31, 2017
Annualized rent | Customer concentration
Concentration of Credit Risk
Number of tenants (tenants) | Tenant		1
Maximum percentage of annualized rent for any one tenant not individually disclosed (percent) (more than)		5.00%
Annualized rent | 11 Madison Avenue | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)		7.60%	7.40%	7.00%
Annualized rent | 1185 Avenue of the Americas | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)		7.40%	6.70%	7.10%
Annualized rent | 420 Lexington Avenue | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)		6.60%	6.00%	6.00%
Annualized rent | 1515 Broadway | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)		6.10%	6.50%	7.10%
Annualized rent | One Madison Ave | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)		6.00%	5.80%	5.60%
Annualized rent | East 220 Street 42 | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)		5.50%
Collective bargaining arrangements | Workforce concentration
Concentration of Credit Risk
Percentage of concentration (percent)		70.10%
Number of collective bargaining agreements | agreement		6
Collective bargaining arrangements expiring in December 2019 | Workforce concentration
Concentration of Credit Risk
Percentage of concentration (percent)		2.10%
Tenant 1 | Annualized rent | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)		8.20%
Subsequent Event | Credit Suisse | Annualized rent | Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	3.30%

Significant Accounting Polici_8

Significant Accounting Policies - Accounting Standards Update (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease, cost	$ 10

Property Acquisitions - 2019 Ac

Property Acquisitions - 2019 Acquisitions (Details) $ in Millions	1 Months Ended
	May 31, 2019USD ($)	Dec. 31, 2019USD ($)ft²
Business Acquisition [Line Items]
Approximate Square Feet | ft²		27,607,971
106 Spring Street
Business Acquisition [Line Items]
Approximate Square Feet | ft²		5,928
Gross Asset Valuation (in millions)		$ 80.2
410 Tenth Avenue
Business Acquisition [Line Items]
Approximate Square Feet | ft²		638,000
Gross Asset Valuation (in millions)		$ 440
Interest acquired	70.87%
Fair value adjustment	$ 67.6
net intangible lease liabilities recognized	$ 18.3
110 Greene Street
Business Acquisition [Line Items]
Approximate Square Feet | ft²		223,600
Gross Asset Valuation (in millions)		$ 256.5
Interest acquired	10.00%

Property Acquisitions - 2018 Ac

Property Acquisitions - 2018 Acquisitions (Details) $ in Millions	1 Months Ended
	Dec. 31, 2018USD ($)ft²	Nov. 30, 2018ft²	Oct. 31, 2018USD ($)ft²	Aug. 31, 2018USD ($)aparcel	Jul. 31, 2018USD ($)ft²	May 31, 2018USD ($)ft²	Dec. 31, 2019ft²
Business Acquisition [Line Items]
Approximate Square Feet | ft²							27,607,971
2 Herald Square
Business Acquisition [Line Items]
Approximate Square Feet | ft²						369,000
Acquisition Price (in millions) | $						$ 266
Purchase price fair value adjustment | $						$ 8.1
1231 Third Avenue
Business Acquisition [Line Items]
Approximate Square Feet | ft²					39,000
Acquisition Price (in millions) | $					$ 55.4
Upper East Side Residential
Business Acquisition [Line Items]
Approximate Square Feet | a				0.2
Acquisition Price (in millions) | $				$ 30.2
Number of land parcels, fee interest acquired | parcel				3
113 Greene Street
Business Acquisition [Line Items]
Approximate Square Feet | ft²			6,425
Acquisition Price (in millions) | $			$ 31
712 Madison Avenue
Business Acquisition [Line Items]
Approximate Square Feet | ft²	6,600
Acquisition Price (in millions) | $	$ 58
2 Herald Square
Business Acquisition [Line Items]
Approximate Square Feet | ft²		369,000
Ownership percentage in disposed asset		49.00%

Properties Held for Sale and _3

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

1 Months Ended

12 Months Ended

Dec. 31, 2019USD ($)ft²

Nov. 30, 2019USD ($)ft²

Aug. 31, 2019USD ($)ft²

Nov. 30, 2018USD ($)ft²a

Oct. 31, 2018USD ($)ft²

Jul. 31, 2018USD ($)ft²

Jun. 30, 2018USD ($)ft²

May 31, 2018USD ($)ft²

Feb. 28, 2018

Jan. 31, 2018USD ($)

Dec. 31, 2017USD ($)ft²

Nov. 30, 2017

Oct. 31, 2017USD ($)ft²

Sep. 30, 2017

Jul. 31, 2017USD ($)ft²

Apr. 30, 2017USD ($)ft²

Dec. 31, 2019USD ($)ft²

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)ft²

Sep. 30, 2019USD ($)

Jan. 01, 2018USD ($)ft²

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

27,607,971

27,607,971

Employee-related liabilities

$ 4,000

$ 0

$ 4,000

$ 11,700

$ 0

Purchase price and other fair value adjustments

$ 69,389

$ 57,385

$ 0

East 220 Street 42

Property Dispositions and Assets Held for Sale

Gross asset valuation

$ 815,000

Suburban

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

1,107,000

1,107,000

Gross asset valuation

$ 229,200

$ 229,200

Gain on Sale

$ 1,800

1640 Flatbush Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

1,000

1,000

Gross asset valuation

$ 16,200

$ 16,200

Gain on Sale

5,500

Employee-related liabilities

$ 2,000

$ 2,000

562 Fifth Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

42,635

42,635

Gross asset valuation

$ 52,400

$ 52,400

Gain on Sale

$ (26,600)

1010 Washington Boulevard

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

143,400

Gross asset valuation

$ 23,100

Gain on Sale

$ (7,100)

Spring Street 115

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

5,218

Gross asset valuation

$ 66,600

Gain on Sale

3,600

Purchase price and other fair value adjustments

$ 3,800

Ownership percentage in disposed asset

49.00%

49.00%

Deconsolidation of ownership interest percentage

51.00%

51.00%

2 Herald Square

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

369,000

Gross asset valuation

$ 265,000

Gain on Sale

$ 0

Ownership percentage in disposed asset

49.00%

400 Summit Lake Drive

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | a

39.5

Gross asset valuation

$ 3,000

Gain on Sale

$ (36,200)

Upper East Side Assemblage

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

70,142

Gross asset valuation

$ 143,800

Gain on Sale

(6,300)

Impairment charge

$ 5,800

1-6 International Drive

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

540,000

Gross asset valuation

$ 55,000

Gain on Sale

$ (2,600)

635 Madison Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

176,530

Gross asset valuation

$ 153,000

Gain on Sale

$ (14,100)

115-117 Stevens Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

178,000

Gross asset valuation

$ 12,000

Gain on Sale

$ (700)

600 Lexington Avenue

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

303,515

Gross asset valuation

$ 305,000

Gain on Sale

$ 23,800

Employee-related liabilities

$ 1,300

1515 Broadway

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

1,750,000

1,750,000

Gross asset valuation

$ 1,950,000

$ 1,950,000

Gain on Sale

$ 0

Joint venture ownership percentage sold

12.87%

30.13%

125 Chubb Way

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

278,000

Gross asset valuation

$ 29,500

Gain on Sale

$ (26,100)

16 Court Street

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

317,600

Gross asset valuation

$ 171,000

Gain on Sale

$ 64,900

Employee-related liabilities

$ 2,500

680-750 Washington Boulevard

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

325,000

Gross asset valuation

$ 97,000

Gain on Sale

$ (44,200)

520 White Plains Road

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

180,000

Gross asset valuation

$ 21,000

Gain on Sale

$ (14,600)

102 Greene Street

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

9,200

Gross asset valuation

$ 43,500

Gain on Sale

4,900

Employee-related liabilities

$ 900

Ownership percentage in disposed asset

90.00%

Joint venture ownership percentage sold

10.00%

102 Greene Street

Property Dispositions and Assets Held for Sale

Investment in joint venture, ownership percentage

10.00%

Development Rights | Upper East Side Assemblage

Property Dispositions and Assets Held for Sale

Unaudited Approximate Usable Square Feet | ft²

31,076

Debt and Preferred Equity Inv_3

Debt and Preferred Equity Investments - Roll Forward of Net Book Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Document Period End Date	Dec. 31, 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Balance at beginning of period	$ 2,099,393	$ 2,114,041
Redemptions/sales/syndications/amortization	(1,190,689)	(994,906)
Net change in loan loss reserves	4,000	(5,750)
Balance at end of period	1,580,306	2,099,393
Debt investment
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Originations/accretion	652,866	834,304
Preferred equity investments
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Originations/accretion	$ 14,736	$ 151,704

Debt and Preferred Equity Inv_4

Debt and Preferred Equity Investments - Debt and Preferred Equity Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Carrying value	$ 1,580,306	$ 2,099,393
Senior Financing	5,560,939
Senior Mortgage Debt
Debt Instrument [Line Items]
Carrying value	342,523
Senior Financing	0
Junior Mortgage Debt
Debt Instrument [Line Items]
Carrying value	31,960
Senior Financing	100,000
Mezzanine Debt
Debt Instrument [Line Items]
Carrying value	966,587
Senior Financing	5,188,939
Preferred Equity
Debt Instrument [Line Items]
Carrying value	239,236
Senior Financing	272,000
Total floating rate
Debt Instrument [Line Items]
Carrying value	618,885
Face Value	622,246
Total floating rate | Senior Mortgage Debt
Debt Instrument [Line Items]
Carrying value	341,513
Face Value	342,861
Total floating rate | Junior Mortgage Debt
Debt Instrument [Line Items]
Carrying value	31,960
Face Value	32,000
Total floating rate | Mezzanine Debt
Debt Instrument [Line Items]
Carrying value	245,412
Face Value	247,385
Total floating rate | Preferred Equity
Debt Instrument [Line Items]
Carrying value	0
Face Value	$ 0
Total floating rate | LIBOR | Minimum | Senior Mortgage Debt
Debt Instrument [Line Items]
Basis spread on variable rate	2.75%
Total floating rate | LIBOR | Minimum | Junior Mortgage Debt
Debt Instrument [Line Items]
Basis spread on variable rate	6.00%
Total floating rate | LIBOR | Minimum | Mezzanine Debt
Debt Instrument [Line Items]
Basis spread on variable rate	4.60%
Total floating rate | LIBOR | Maximum | Senior Mortgage Debt
Debt Instrument [Line Items]
Basis spread on variable rate	5.50%
Total floating rate | LIBOR | Maximum | Junior Mortgage Debt
Debt Instrument [Line Items]
Basis spread on variable rate	7.25%
Total floating rate | LIBOR | Maximum | Mezzanine Debt
Debt Instrument [Line Items]
Basis spread on variable rate	12.36%
Total fixed rate
Debt Instrument [Line Items]
Carrying value	$ 961,421
Face Value	974,371
Total fixed rate | Senior Mortgage Debt
Debt Instrument [Line Items]
Carrying value	1,010
Face Value	1,250
Total fixed rate | Junior Mortgage Debt
Debt Instrument [Line Items]
Carrying value	0
Face Value	0
Total fixed rate | Mezzanine Debt
Debt Instrument [Line Items]
Carrying value	721,175
Face Value	728,138
Total fixed rate | Preferred Equity
Debt Instrument [Line Items]
Carrying value	239,236
Face Value	$ 244,983
Total fixed rate | Minimum | Mezzanine Debt
Debt Instrument [Line Items]
Interest rate	2.90%
Total fixed rate | Minimum | Preferred Equity
Debt Instrument [Line Items]
Interest rate	7.00%
Total fixed rate | Maximum | Mezzanine Debt
Debt Instrument [Line Items]
Interest rate	10.00%
Total fixed rate | Maximum | Preferred Equity
Debt Instrument [Line Items]
Interest rate	11.00%

Debt and Preferred Equity Inv_5

Debt and Preferred Equity Investments - Rollforward of Total Allowance for Loan Loss Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loan loss reserve activity
Balance at beginning of year	$ 5,750	$ 0	$ 0
Expensed	0	6,839	0
Recoveries	0	0	0
Charge-offs and reclassifications	(4,000)	(1,089)	0
Balance at end of year	$ 1,750	$ 5,750	$ 0

Debt and Preferred Equity Inv_6

Debt and Preferred Equity Investments - Debt Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Mortgage loans on real estate, interest rate	8.42%
Debt Investments Held [Abstract]
Carrying value	$ 1,580,306	$ 2,099,393
Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Amount participated out	1,300
Mezzanine Loan with an Initial Maturity Date of June 2024
Debt Investments Held [Abstract]
Amount participated out	12,000
Mortgage/Mezzanine Loan With An Initial Maturity Due April 2021
Debt Investments Held [Abstract]
Amount participated out	96,400
Debt investment
Debt Investments Held [Abstract]
Future Funding Obligations	138,672
Senior Financing	5,288,939
Carrying value	1,341,070	1,812,936
Total fixed rate
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	4,115,114
Carrying Value	646,612	430,099
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of March 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,160,000
Carrying Value	222,775	213,185
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of September 2021
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	15,000
Carrying Value	3,500	3,500
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of April 2022
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	147,000
Carrying Value	24,952	24,932
Total fixed rate | Mezzanine Loan With An Initial Maturity Of August 2022
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	280,000
Carrying Value	38,734	36,585
Total fixed rate | Mezzanine Loan With Maturity June 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	326,574
Carrying Value	215,737	0
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of November 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	83,790
Carrying Value	12,714	12,706
Total fixed rate | Mezzanine Loan With An Initial Maturity Date Of December 2023
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	180,000
Carrying Value	30,000	30,000
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
Carrying Value	12,950	12,941
Total fixed rate | Mezzanine Loan, with an Initial Maturity Date of January 2025
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	95,000
Carrying Value	30,000	30,000
Total fixed rate | Mezzanine Loan with an Initial Maturity Date of June 2027
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	1,712,750
Carrying Value	55,250	55,250
Total fixed rate | Mezzanine Loan Sold In 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying Value	0	11,000
Total floating rate
Debt Investments Held [Abstract]
Future Funding Obligations	138,672
Senior Financing	1,173,825
Carrying value	694,458	1,382,837
Total floating rate | Mezzanine Loan with an Initial Maturity of January 2020
Debt Investments Held [Abstract]
Future Funding Obligations	2,509
Senior Financing	29,420
Carrying value	82,696	62,493
Total floating rate | Mortgage/Mezzanine Loan Due March 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	69,839	0
Total floating rate | Mortgage and Mezzanine Loan with an Initial Maturity Date of April 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	40,000
Carrying value	20,000	19,986
Total floating rate | Mezzanine Loan with an Initial Maturity of July 2020
Debt Investments Held [Abstract]
Future Funding Obligations	4,831
Senior Financing	47,302
Carrying value	15,743	12,627
Total floating rate | Mortgage/Mezzanine Loan Due August 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	19,971	19,999
Total floating rate | Mezzanine Loan Due September 2020
Debt Investments Held [Abstract]
Future Funding Obligations	44,737
Senior Financing	0
Carrying value	106,473	88,501
Total floating rate | Mortgage And Mezzanine Loan With An Initial Maturity Date Of October 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	63,990
Carrying value	55,573	83,449
Total floating rate | Mezzanine Loan Due December 2021
Debt Investments Held [Abstract]
Future Funding Obligations	19,212
Senior Financing	421,938
Carrying value	51,387	88,817
Total floating rate | Mortgage/Mezzanine Loan with an Initial Maturity of December 2020
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	35,386	35,266
Total floating rate | Mortgage/Mezzanine Loan With An Initial Maturity Due April 2021
Debt Investments Held [Abstract]
Future Funding Obligations	10,384
Senior Financing	0
Carrying value	96,570	277,694
Total floating rate | Mezzanine Loan With An Initial Maturity Due April 2021
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	275,000
Carrying value	49,809	24,961
Total floating rate | Jr Mortgage Participation/Mezzanine Loan with an Initial Maturity of July 2021
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	60,000
Carrying value	15,698	15,665
Total floating rate | Mezzanine Loan With An Initial Maturity Due July 2021
Debt Investments Held [Abstract]
Future Funding Obligations	12,999
Senior Financing	151,175
Carrying value	41,395	0
Total floating rate | Mezzanine Loan Due December 2022
Debt Investments Held [Abstract]
Future Funding Obligations	44,000
Senior Financing	0
Carrying value	13,918	0
Total floating rate | Mezzanine Loan Due December 2029
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	85,000
Carrying value	20,000	0
Total floating rate | Mezzanine Loan Repaid In 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	53,402
Total floating rate | Mezzanine Loan Repaid In 2019, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	79,164
Total floating rate | Mezzanine Loan Repaid In 2019, 3
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	15,333
Total floating rate | Mezzanine Loan Repaid In 2019, 4
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	14,822
Total floating rate | Mortgage And Mezzanine Loan Repaid In 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	154,070
Total floating rate | Mezzanine Loan Repaid In 2019, 5
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	34,886
Total floating rate | Mortgage/Jr.Mortgage Participation Loan Repaid In 2019
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	84,012
Total floating rate | Mortgage And Mezzanine Loan Repaid In 2019, 2
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	37,094
Total floating rate | Mortgage And Mezzanine Loan Repaid In 2019, 3
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	98,804
Total floating rate | Mezzanine Loan Repaid In 2019, 6
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	7,305
Total floating rate | Mezzanine Loan Repaid In 2019, 7
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	14,998
Total floating rate | Mezzanine Loan Repaid In 2019, 8
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	0	21,990
Total floating rate | Mezzanine Loan Repaid In 2019, 9
Debt Investments Held [Abstract]
Future Funding Obligations	0
Senior Financing	0
Carrying value	$ 0	$ 37,499

Debt and Preferred Equity Inv_7

Debt and Preferred Equity Investments - Preferred Equity Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Preferred equity investment
Mortgage loans on real estate, interest rate	8.42%
Carrying value	$ 1,580,306	$ 2,099,393
Preferred Equity, April 2021
Preferred equity investment
Future Funding Obligations	0
Senior Financing	272,000
Carrying value	141,171	143,183
Preferred Equity Redeemed in May 2017
Preferred equity investment
Future Funding Obligations	0
Senior Financing	1,763,529
Carrying value	$ 98,065	143,274
Preferred equity investments
Preferred equity investment
Mortgage loans on real estate, interest rate	9.63%
Future Funding Obligations	$ 0
Senior Financing	2,035,529
Carrying value	$ 239,236	$ 286,457

Debt and Preferred Equity Inv_8

Debt and Preferred Equity Investments - Narrative (Details)	12 Months Ended
	Dec. 31, 2019USD ($)segmentloan	Dec. 31, 2018USD ($)segmentloan	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Preferred equity investment
Allowance for loan and lease losses	$ 1,750,000	$ 5,750,000	$ 0	$ 0
Number of investments marketed for sale | loan	1	2
Unpaid principal balance	$ 142,900,000	$ 159,900,000
Carrying value	$ 1,580,306,000	$ 2,099,393,000
Number of portfolio segments of financial receivables (segment) | segment	1	1
Additional amount of financing receivables included in other assets	$ 131,100,000	$ 124,500,000
Financing receivable, nonaccrual status	$ 28,400,000
Weighted average risk rating	1.2
Financing Receivables, Equal to Greater than 90 Days Past Due
Preferred equity investment
Financing receivable, past due	$ 0

Investments in Unconsolidated_3

Investments in Unconsolidated Joint Ventures - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Oct. 31, 2016	Dec. 31, 2019USD ($)ft²unit	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)ft²unit	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
General information on each joint venture
Investments in unconsolidated joint ventures | $		$ 2,912,842				$ 3,019,020				$ 2,912,842	$ 3,019,020
Net equity investment in VIEs | $		$ 145,900				808,300				$ 145,900	808,300
Approximate Square Feet		27,607,971								27,607,971
Purchase price and other fair value adjustment | $		$ 0	$ 3,799	$ 67,631	$ (2,041)	$ 0	$ (3,057)	$ 11,149	$ 49,293	$ 69,389	$ 57,385	$ 0
21 East 66th Street | Three Retail and Two Residential Units
General information on each joint venture
Ownership Interest Sold		32.28%								32.28%
Number of Stores | unit		3								3
Number of residential units | unit		1								1
21 East 66th Street | Three Residential Units
General information on each joint venture
Ownership Interest Sold		16.14%								16.14%
Number of residential units | unit		3								3
Stonehenge Portfolio
General information on each joint venture
Ownership Interest Sold	90.00%
400 East 57th Street
General information on each joint venture
Ownership Interest Sold	51.00%
1552 Broadway
General information on each joint venture
Approximate Square Feet		13,045								13,045
Joint venture
General information on each joint venture
Investments in unconsolidated joint ventures | $		$ 2,912,842								$ 2,912,842
Equity method investments with negative book value | $		$ 80,900								$ 80,900
Joint venture | 100 Park Avenue
General information on each joint venture
Ownership Interest Sold		49.90%								49.90%
Economic Interest, percent		49.90%								49.90%
Approximate Square Feet		834,000								834,000
Joint venture | 717 Fifth Avenue
General information on each joint venture
Ownership Interest Sold		10.92%								10.92%
Economic Interest, percent		10.92%								10.92%
Approximate Square Feet		119,500								119,500
Joint venture | 800 Third Avenue
General information on each joint venture
Ownership Interest Sold		60.52%								60.52%
Economic Interest, percent		60.52%								60.52%
Approximate Square Feet		526,000								526,000
Joint venture | 919 Third Avenue
General information on each joint venture
Ownership Interest Sold		51.00%								51.00%
Economic Interest, percent		51.00%								51.00%
Approximate Square Feet		1,454,000								1,454,000
Joint venture | 11 West 34th Street
General information on each joint venture
Ownership Interest Sold		30.00%								30.00%
Economic Interest, percent		30.00%								30.00%
Approximate Square Feet		17,150								17,150
Joint venture | 280 Park Avenue
General information on each joint venture
Ownership Interest Sold		50.00%								50.00%
Economic Interest, percent		50.00%								50.00%
Approximate Square Feet		1,219,158								1,219,158
Joint venture | 1552 Broadway
General information on each joint venture
Ownership Interest Sold		50.00%								50.00%
Economic Interest, percent		50.00%								50.00%
Approximate Square Feet		57,718								57,718
Joint venture | 10 East 53rd Street
General information on each joint venture
Ownership Interest Sold		55.00%								55.00%
Economic Interest, percent		55.00%								55.00%
Approximate Square Feet		354,300								354,300
Joint venture | 21 East 66th Street
General information on each joint venture
Ownership Interest Sold		32.28%								32.28%
Economic Interest, percent		32.28%								32.28%
Approximate Square Feet		13,069								13,069
Joint venture | 650 Fifth Avenue
General information on each joint venture
Ownership Interest Sold		50.00%								50.00%
Economic Interest, percent		50.00%								50.00%
Approximate Square Feet		69,214								69,214
Joint venture | 121 Greene Street
General information on each joint venture
Ownership Interest Sold		50.00%								50.00%
Economic Interest, percent		50.00%								50.00%
Approximate Square Feet		7,131								7,131
Joint venture | 55 West 46th Street
General information on each joint venture
Ownership Interest Sold		25.00%								25.00%
Economic Interest, percent		25.00%								25.00%
Approximate Square Feet		347,000								347,000
Joint venture | Stonehenge Portfolio
General information on each joint venture
Ownership Interest Sold	10.00%
Approximate Square Feet		1,439,016								1,439,016
Joint venture | 605 West 42nd Street
General information on each joint venture
Ownership Interest Sold		20.00%								20.00%
Economic Interest, percent		20.00%								20.00%
Approximate Square Feet		927,358								927,358
Joint venture | 11 Madison Avenue
General information on each joint venture
Ownership Interest Sold		60.00%								60.00%
Economic Interest, percent		60.00%								60.00%
Approximate Square Feet		2,314,000								2,314,000
Joint venture | 333 East 22nd St
General information on each joint venture
Ownership Interest Sold		33.33%								33.33%
Economic Interest, percent		33.33%								33.33%
Approximate Square Feet		26,926								26,926
Joint venture | 400 East 57th Street
General information on each joint venture
Ownership Interest Sold		51.00%								51.00%
Economic Interest, percent		41.00%								41.00%
Approximate Square Feet		290,482								290,482
Joint venture | One Vanderbilt
General information on each joint venture
Ownership Interest Sold		71.01%								71.01%
Economic Interest, percent		71.01%								71.01%
Approximate Square Feet		0								0
Joint venture | Worldwide Plaza
General information on each joint venture
Ownership Interest Sold		24.35%								24.35%
Economic Interest, percent		24.35%								24.35%
Approximate Square Feet		2,048,725								2,048,725
Joint venture | 1515 Broadway
General information on each joint venture
Ownership Interest Sold		56.87%								56.87%
Economic Interest, percent		56.87%								56.87%
Approximate Square Feet		1,750,000								1,750,000
Joint venture | 2 Herald Square
General information on each joint venture
Ownership Interest Sold		51.00%								51.00%
Economic Interest, percent		51.00%								51.00%
Approximate Square Feet		369,000								369,000
Joint venture | Spring Street 115
General information on each joint venture
Ownership Interest Sold		51.00%								51.00%
Economic Interest, percent		51.00%								51.00%
Approximate Square Feet		5,218								5,218
919 Third Avenue | Joint venture | 919 Third Avenue
General information on each joint venture
Purchase price and other fair value adjustment | $										$ 49,300
400 East 57th Street
General information on each joint venture
Ownership percentage in disposed asset	49.00%

Investments in Unconsolidated_4

Investments in Unconsolidated Joint Ventures - Acquisition, Development and Construction Arrangements/Sale of Joint Venture Interest or Property (Details) $ in Thousands	1 Months Ended											3 Months Ended								12 Months Ended
	Dec. 31, 2019USD ($)note	May 31, 2019USD ($)	Jan. 31, 2019USD ($)	Nov. 30, 2018USD ($)	Jul. 31, 2018USD ($)	Jun. 30, 2018USD ($)	May 31, 2018USD ($)	Apr. 30, 2018USD ($)	Feb. 28, 2018USD ($)	Sep. 30, 2017USD ($)	May 31, 2017USD ($)	Dec. 31, 2019USD ($)note	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)note	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Aug. 31, 2018USD ($)	Apr. 30, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures	$ 2,912,842											$ 2,912,842				$ 3,019,020				$ 2,912,842	$ 3,019,020
Gain (Loss) on Sale												0	$ 0	$ 59,015	$ 17,166	167,445	$ 70,937	$ 72,025	$ (6,440)	76,181	303,967	$ 16,166
Employee-related liabilities	4,000											4,000				11,700				4,000	11,700	0
(Loss) gain on sale of real estate, net												(19,241)	$ 3,541	$ 0	$ (1,049)	(36,984)	$ (2,504)	$ (14,790)	$ 23,521	(16,749)	(30,757)	73,241
Madison Avenue 747
Schedule of Equity Method Investments [Line Items]
(Loss) gain on sale of real estate, net											$ 13,000
Participating Financing Due February 2022
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures	0											0				44,357				0	44,357
Mezzanine Loans And Preferred Equity
Schedule of Equity Method Investments [Line Items]
Acquisition, development and construction arrangements, carrying value	$ 0											$ 0				44,357				$ 0	44,357
1515 Broadway
Schedule of Equity Method Investments [Line Items]
Gross asset valuation																						1,950,000
102 Greene Street
Schedule of Equity Method Investments [Line Items]
Gross asset valuation																								$ 43,500
Employee-related liabilities																								$ 900
76 11th Avenue
Schedule of Equity Method Investments [Line Items]
Number of notes owned | note	2											2								2
Joint venture
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures	$ 2,912,842											$ 2,912,842								$ 2,912,842
Joint venture | East 21 Street 66
Schedule of Equity Method Investments [Line Items]
Gross asset valuation	2,900											2,900								2,900
Gain (Loss) on Sale	279
Joint venture | Fifth Avenue, 521
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold		50.50%
Gross asset valuation		$ 381,000
Gain (Loss) on Sale		$ 57,874
Joint venture | Spring Street 131 to 137
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold			20.00%
Gross asset valuation			$ 216,000
Gain (Loss) on Sale			$ 17,660
Joint venture | Stonehenge Portfolio
Schedule of Equity Method Investments [Line Items]
Gross asset valuation	$ 468,800											$ 468,800				$ 331,100				468,800	331,100	300,000
Gain (Loss) on Sale																				$ (2,408)	$ (6,063)	$ 871
Joint venture | 3 Columbus Circle
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold				48.90%
Gross asset valuation				$ 851,000
Gain (Loss) on Sale				$ 160,368
Joint venture | Mezzanine Loan
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold																							33.33%
Gross asset valuation																							$ 15,000
Joint venture | 724 Fifth Avenue
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold					49.90%
Gross asset valuation					$ 365,000
Gain (Loss) on Sale					$ 64,587
Joint venture | Jericho Plaza
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold						11.67%												11.67%
Gross asset valuation						$ 117,400												$ 117,400
Gain (Loss) on Sale						$ 147
Joint venture | 1745 Broadway
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold							56.87%
Gross asset valuation							$ 633,000
Gain (Loss) on Sale							$ 52,038
Joint venture | 175-225 Third Street Brooklyn, New York
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold								95.00%
Gross asset valuation								$ 115,000
Gain (Loss) on Sale								$ 19,483
Joint venture | 1515 Broadway
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold									13.00%
Gross asset valuation									$ 1,950,000
Gain (Loss) on Sale									$ 0
Joint venture | 102 Greene Street
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold										10.00%
Gross asset valuation										$ 43,500
Gain (Loss) on Sale										$ 283
Joint venture | 76 11th Avenue
Schedule of Equity Method Investments [Line Items]
Ownership Interest Sold											33.33%
Gross asset valuation											$ 138,240

Investments in Unconsolidated_5

Investments in Unconsolidated Joint Ventures - Mortgages and Other Loans Payable (Details)	12 Months Ended
	Dec. 31, 2019USD ($)extension	Aug. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
Total fixed rate debt	$ 1,383,449,000		$ 1,389,717,000
Total floating rate debt	828,434,000		598,442,000
Deferred financing costs, net	(28,630,000)		(26,919,000)
115 Spring Street
Debt Instrument [Line Items]
Total floating rate debt			65,550,000
Joint venture
Debt Instrument [Line Items]
Total fixed rate debt	5,351,721,000		5,666,108,000
Total floating rate debt	3,691,686,000		3,387,705,000
Total fixed rate and floating rate debt	9,043,407,000		9,053,813,000
Deferred financing costs, net	(91,538,000)		(103,191,000)
Total joint venture mortgages and other loans payable, net	$ 8,951,869,000		8,950,622,000
Joint venture | 717 Fifth Avenue
Debt Instrument [Line Items]
Economic Interest, 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
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
Joint venture | 650 Fifth Avenue
Debt Instrument [Line Items]
Economic Interest, 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
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, 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	$ 712,000		1,571,000
Joint venture | 919 Third Avenue
Debt Instrument [Line Items]
Economic Interest, percent	51.00%
Interest rate, fixed rate debt (as a percent)	5.12%
Total fixed rate debt	$ 500,000,000		500,000,000
Joint venture | 1515 Broadway
Debt Instrument [Line Items]
Economic Interest, percent	56.87%
Interest rate, fixed rate debt (as a percent)	3.93%
Total fixed rate debt	$ 838,546,000		855,876,000
Joint venture | 11 Madison Avenue
Debt Instrument [Line Items]
Economic Interest, percent	60.00%
Interest rate, fixed rate debt (as a percent)	3.84%
Total fixed rate debt	$ 1,400,000,000		1,400,000,000
Joint venture | 800 Third Avenue
Debt Instrument [Line Items]
Economic Interest, percent	60.52%
Interest rate, fixed rate debt (as a percent)	3.37%
Total fixed rate debt	$ 177,000,000		177,000,000
Joint venture | 400 East 57th Street
Debt Instrument [Line Items]
Economic Interest, percent	41.00%
Interest rate, fixed rate debt (as a percent)	3.00%
Total fixed rate debt	$ 97,735,000		99,828,000
Joint venture | Worldwide Plaza
Debt Instrument [Line Items]
Economic Interest, percent	24.35%
Interest rate, fixed rate debt (as a percent)	3.98%
Total fixed rate debt	$ 1,200,000,000		1,200,000,000
Joint venture | Stonehenge Portfolio
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.50%
Total fixed rate debt	$ 196,112,000		321,076,000
Joint venture | Stonehenge Portfolio | Initial Maturity August 2019
Debt Instrument [Line Items]
Total fixed rate debt	132,600,000
Joint venture | Stonehenge Portfolio | Initial Maturity June 2024
Debt Instrument [Line Items]
Total fixed rate debt	63,500,000
Joint venture | 521 Fifth Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 0		170,000,000
Joint venture | 10 East 53rd Street
Debt Instrument [Line Items]
Economic Interest, percent	55.00%
Interest rate, floating rate debt (as a percent)	2.25%
Total floating rate debt	$ 170,000,000		170,000,000
Joint venture | 280 Park Avenue
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Interest rate, floating rate debt (as a percent)	1.73%
Total floating rate debt	$ 1,200,000,000		1,200,000,000
Joint venture | 1552 Broadway
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Interest rate, floating rate debt (as a percent)	2.65%
Total floating rate debt	$ 195,000,000		195,000,000
Joint venture | 121 Greene Street
Debt Instrument [Line Items]
Economic Interest, percent	50.00%
Interest rate, floating rate debt (as a percent)	1.50%
Total floating rate debt	$ 15,000,000		15,000,000
Joint venture | 11 West 34th Street
Debt Instrument [Line Items]
Economic Interest, percent	30.00%
Interest rate, floating rate debt (as a percent)	1.45%
Total floating rate debt	$ 23,000,000		23,000,000
Joint venture | 100 Park Avenue
Debt Instrument [Line Items]
Economic Interest, percent	49.90%
Interest rate, floating rate debt (as a percent)	1.75%
Total floating rate debt	$ 356,972,000		360,000,000
Joint venture | One Vanderbilt
Debt Instrument [Line Items]
Economic Interest, percent	71.01%
Interest rate, floating rate debt (as a percent)	2.50%
Total floating rate debt	$ 732,928,000		375,000,000
Joint venture | One Vanderbilt | Construction Loans
Debt Instrument [Line Items]
Maximum facility capacity	$ 1,750,000,000
Term (in Years)	5 years
Number of extension options | extension	2
Period of extension option	1 year
Joint venture | 2 Herald Square
Debt Instrument [Line Items]
Economic Interest, percent	51.00%
Interest rate, floating rate debt (as a percent)	1.45%
Total floating rate debt	$ 190,000,000		133,565,000
Joint venture | 55 West 46th Street
Debt Instrument [Line Items]
Economic Interest, percent	25.00%
Interest rate, floating rate debt (as a percent)	1.25%
Total floating rate debt	$ 192,524,000		185,569,000
Joint venture | 55 West 46th Street | Mortgage loan
Debt Instrument [Line Items]
Face amount of loan		$ 192,500,000
Committed amount		198,000,000
Debt instrument unfunded amount		$ 5,500,000
Joint venture | 115 Spring Street
Debt Instrument [Line Items]
Economic Interest, percent	51.00%
Interest rate, floating rate debt (as a percent)	3.40%
Total floating rate debt	$ 65,550,000		0
Joint venture | 605 West 42nd Street
Debt Instrument [Line Items]
Economic Interest, percent	20.00%
Interest rate, floating rate debt (as a percent)	1.44%
Total floating rate debt	$ 550,000,000		550,000,000
Joint venture | 131-137 Spring Street
Debt Instrument [Line Items]
Total floating rate debt	0		141,000,000
Joint venture | 103 East 86th Street
Debt Instrument [Line Items]
Total floating rate debt	$ 0		$ 38,000,000

Investments in Unconsolidated_6

Investments in Unconsolidated Joint Ventures - Schedules of Combined Financial Statements for the Unconsolidated Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets
Commercial real estate property, net	$ 6,724,007				$ 6,414,798				$ 6,724,007	$ 6,414,798
Cash and restricted cash	166,070				129,475				166,070	129,475	$ 127,888
Tenant and other receivables and deferred rents receivable	43,968				41,589				43,968	41,589
Debt and preferred equity investments	1,580,306				2,099,393				1,580,306	2,099,393
Other assets	332,801				295,679				332,801	295,679
Liabilities and equity
Mortgages and other loans payable, net	2,183,253				1,961,240				2,183,253	1,961,240
Lease liabilities	381,671				3,603				381,671	3,603
Other liabilities	177,080				116,566				177,080	116,566
Company's investments in unconsolidated joint ventures	2,912,842				3,019,020				2,912,842	3,019,020
Investments difference between carrying amount and underlying equity	133,100								133,100
Combined statements of income for the unconsolidated joint ventures
Real estate taxes									190,764	186,351	244,323
Amortization of deferred financing costs									11,653	12,408	16,498
Transaction related costs									729	1,099	(1,834)
Depreciation and amortization									272,358	279,507	403,320
Total expenses	252,712	$ 263,341	$ 258,383	$ 260,328	267,678	$ 265,553	$ 258,303	$ 258,282	1,034,764	1,049,816	1,346,445
Company's equity in net (loss) income from unconsolidated joint ventures	(11,874)	$ (9,864)	$ (7,546)	$ (5,234)	(2,398)	$ 971	$ 4,702	$ 4,036	(34,518)	7,311	21,892
Joint venture
Assets
Commercial real estate property, net	14,349,628				14,347,673				14,349,628	14,347,673
Cash and restricted cash	336,189				381,301				336,189	381,301
Tenant and other receivables and deferred rents receivable	371,065				273,141				371,065	273,141
Debt and preferred equity investments	0				44,357				0	44,357
Other assets	2,039,429				2,187,166				2,039,429	2,187,166
Total assets	17,096,311				17,233,638				17,096,311	17,233,638
Liabilities and equity
Mortgages and other loans payable, net	8,951,869				8,950,622				8,951,869	8,950,622
Deferred revenue	1,501,616				1,660,838				1,501,616	1,660,838
Lease liabilities	897,380				637,168				897,380	637,168
Other liabilities	308,304				309,145				308,304	309,145
Equity	5,437,142				5,675,865				5,437,142	5,675,865
Total liabilities and equity	17,096,311				$ 17,233,638				17,096,311	17,233,638
Company's investments in unconsolidated joint ventures	$ 2,912,842								2,912,842
Combined statements of income for the unconsolidated joint ventures
Total revenues									1,163,534	1,244,804	904,230
Operating expenses									202,881	219,440	157,610
Real estate taxes									212,355	226,961	142,774
Operating lease, rent									24,816	18,697	16,794
Interest expense, net of interest income									372,408	363,055	250,063
Amortization of deferred financing costs									19,336	21,634	23,026
Transaction related costs									0	0	146
Depreciation and amortization									407,697	421,458	279,419
Total expenses									1,239,493	1,271,245	869,832
Loss on early extinguishment of debt									(1,031)	0	(7,899)
Net (loss) income before gain on sale									(76,990)	(26,441)	26,499
Company's equity in net (loss) income from unconsolidated joint ventures									(34,518)	7,311	21,892
Management Service, Base | Joint venture
Investment in Unconsolidated Joint Ventures
Management fees, base revenue									$ 13,000	$ 14,200	$ 22,600

Deferred Costs (Details)

Deferred Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred leasing costs	$ 466,136	$ 453,833
Less: accumulated amortization	(260,853)	(244,723)
Deferred costs, net	$ 205,283	$ 209,110

Mortgages and Other Loans Pay_3

Mortgages and Other Loans Payable (Details)	1 Months Ended					12 Months Ended
	Feb. 24, 2020USD ($)	Jan. 31, 2020USD ($)	Aug. 31, 2019extension	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2019USD ($)extension	Dec. 31, 2018USD ($)	Apr. 30, 2018USD ($)
Debt Instrument [Line Items]
Total fixed rate debt						$ 1,383,449,000	$ 1,389,717,000
Total floating rate debt						828,434,000	598,442,000
Total mortgages and other loans payable						2,211,883,000	1,988,159,000
Deferred financing costs, net of amortization						(28,630,000)	(26,919,000)
Total mortgages and other loans payable						2,183,253,000	1,961,240,000
Book value of collateral						3,300,000,000	2,600,000,000
Outstanding under line of credit facility						234,013,000	492,196,000
FHLB Facility January 2020
Debt Instrument [Line Items]
Total floating rate debt						$ 10,000,000	0
FHLB Facility January 2020 | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						0.26%
FHLB Facility February 2020
Debt Instrument [Line Items]
Total floating rate debt						$ 15,000,000	0
FHLB Facility February 2020 | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						0.32%
FHLB Facility June 2020
Debt Instrument [Line Items]
Total floating rate debt						$ 14,500,000	0
FHLB Facility June 2020 | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						0.17%
2017 Master Repurchase Agreement
Debt Instrument [Line Items]
Total floating rate debt						$ 152,684,000	300,000,000
Maximum facility capacity						300,000,000		$ 400,000,000
Number of extension options | extension			2
Number of extension option			1 year	1 year	1 year
Outstanding under line of credit facility						$ 152,400,000
2017 Master Repurchase Agreement | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						2.19%
FHLB Facility, August 2019
Debt Instrument [Line Items]
Total floating rate debt							13,000,000
FHLB Facility, December 2019
Debt Instrument [Line Items]
Total floating rate debt							14,500,000
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						$ 209,296,000	213,208,000
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						$ 299,165,000	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						$ 39,094,000	39,931,000
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						$ 35,123,000	35,807,000
1080 Amsterdam Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)						3.59%
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%
A133 Greene Street
Debt Instrument [Line Items]
Total floating rate debt						$ 15,523,000	15,523,000
A133 Greene Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						2.00%
106 Spring Street
Debt Instrument [Line Items]
Total floating rate debt						$ 38,025,000	0
106 Spring Street | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						2.50%
609 Fifth Avenue
Debt Instrument [Line Items]
Total floating rate debt						$ 53,773,000	0
609 Fifth Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						2.40%
185 Broadway
Debt Instrument [Line Items]
Total floating rate debt						$ 120,110,000	111,869,000
185 Broadway | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						2.85%
712 Madison Avenue
Debt Instrument [Line Items]
Total floating rate debt						$ 28,000,000	28,000,000
712 Madison Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						1.85%
410 Tenth Avenue
Debt Instrument [Line Items]
Total floating rate debt						$ 330,819,000	0
410 Tenth Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						2.23%
719 Seventh Avenue
Debt Instrument [Line Items]
Total floating rate debt						$ 50,000,000	50,000,000
719 Seventh Avenue | Weighted Average
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)						1.20%
1080 Amsterdam
Debt Instrument [Line Items]
Total fixed rate debt						$ 34,200,000
Subordinate loan						$ 900,000
1080 Amsterdam | Weighted Average
Debt Instrument [Line Items]
Term (in Years)						5 years
1080 Amsterdam | Mortgage loan | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)						3.50%
1080 Amsterdam | Senior Subordinated Loans | Weighted Average
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)						7.00%
115 Spring Street
Debt Instrument [Line Items]
Total floating rate debt							$ 65,550,000
Construction Loans | 185 Broadway
Debt Instrument [Line Items]
Term (in Years)						3 years
Maximum facility capacity						$ 225,000,000
Number of extension options | extension						2
Period of extension option						1 year
Construction Loans | 410 Tenth Avenue
Debt Instrument [Line Items]
Maximum facility capacity						$ 465
Number of extension options | extension						2
Construction Loans | 460 West 34th Street
Debt Instrument [Line Items]
Term (in Years)						3 years
Period of extension option						1 year
LIBOR Plus 25 Basis Points | Ticonderoga
Debt Instrument [Line Items]
FHLB advances						$ 39,500,000
LIBOR Plus 25 Basis Points | Ticonderoga | LIBOR
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)						0.25%
115 Spring Street
Debt Instrument [Line Items]
Ownership percentage in disposed asset			49.00%			49.00%
Deconsolidation of ownership interest percentage			51.00%			51.00%
Subsequent Event | FHLB Facility January 2020
Debt Instrument [Line Items]
Face amount of loan		$ 10,000,000
Interest rate added to base rate (as a percent)		0.165%
Subsequent Event | FHLB Facility February 2020
Debt Instrument [Line Items]
Face amount of loan	$ 15,000,000
Interest rate added to base rate (as a percent)	0.26%

Corporate Indebtedness - Additi

Corporate Indebtedness - Additional Information (Details)	1 Months Ended	12 Months Ended
	May 31, 2019	Dec. 31, 2019USD ($)extension	Dec. 31, 2018USD ($)
Corporate Indebtedness
Outstanding under line of credit facility		$ 234,013,000	$ 492,196,000
Long-term debt		$ 2,183,253,000	1,961,240,000
Term Loan B, Maturity November 21, 2024 | LIBOR
Corporate Indebtedness
Interest rate added to base rate (as a percent)	6500.00%
Term Loan B, Maturity November 21, 2024 | LIBOR | Minimum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	8500.00%
Term Loan B, Maturity November 21, 2024 | LIBOR | Maximum
Corporate Indebtedness
Interest rate added to base rate (as a percent)	16500.00%
Revolving credit facility
Corporate Indebtedness
Facility fee (as a percent)		0.20%
Outstanding under line of credit facility		$ 240,000,000
Revolving credit facility | Minimum
Corporate Indebtedness
Facility fee (as a percent)		0.125%
Revolving credit facility | Maximum
Corporate Indebtedness
Facility fee (as a percent)		0.30%
2012 Credit Facility
Corporate Indebtedness
Credit facility, maximum borrowing capacity		$ 1,500,000,000
Letters of credit		11,800,000
Ability to borrow under line of credit facility		1,300,000,000
Line of Credit | Term loan
Corporate Indebtedness
Long-term debt		1,500,000,000	1,500,000,000
Line of Credit | 2012 Credit Facility
Corporate Indebtedness
Long-term debt		234,000,000	$ 492,200,000
Term loan | Term Loan A, Maturity March 31, 2023
Corporate Indebtedness
Credit facility, maximum borrowing capacity		$ 1,300,000,000
Term loan | Term Loan A, Maturity March 31, 2023 | LIBOR
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.10%
Term loan | Term Loan A, Maturity March 31, 2023 | LIBOR | Minimum
Corporate Indebtedness
Interest rate added to base rate (as a percent)		0.90%
Term loan | Term Loan A, Maturity March 31, 2023 | LIBOR | Maximum
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.75%
Term loan | Term Loan B, Maturity November 21, 2024
Corporate Indebtedness
Credit facility, maximum borrowing capacity		$ 200,000,000
Term loan | Term Loan B, Maturity November 21, 2024 | LIBOR
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.00%
Term loan | Term Loan B, Maturity November 21, 2024 | LIBOR | Minimum
Corporate Indebtedness
Interest rate added to base rate (as a percent)		0.85%
Term loan | Term Loan B, Maturity November 21, 2024 | LIBOR | Maximum
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.65%
Revolving credit facility | Line of Credit | Revolving Credit Facility, Maturity March 31, 2022
Corporate Indebtedness
Credit facility, maximum borrowing capacity		$ 1,500,000,000
Number of extensions | extension		2
Term of extension		6 months
Maximum borrowing capacity, optional expansion		$ 4,500,000,000
Revolving credit facility | Line of Credit | Revolving Credit Facility, Maturity March 31, 2022 | LIBOR
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.00%
Revolving credit facility | Line of Credit | Revolving Credit Facility, Maturity March 31, 2022 | LIBOR | Minimum
Corporate Indebtedness
Interest rate added to base rate (as a percent)		0.825%
Revolving credit facility | Line of Credit | Revolving Credit Facility, Maturity March 31, 2022 | LIBOR | Maximum
Corporate Indebtedness
Interest rate added to base rate (as a percent)		1.55%

Corporate Indebtedness - Senior

Corporate Indebtedness - Senior Unsecured Notes (Details) - USD ($)	1 Months Ended	12 Months Ended
	Oct. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 5,551,883,000
Accreted Balance		1,496,847,000	$ 1,495,214,000
Deferred financing costs, net		(28,630,000)	(26,919,000)
Senior Unsecured Bonds | 4.50% Senior Unsecured Bonds Due December 2022
Debt disclosures by scheduled maturity date
Coupon Rate (as a percent)	4.50%
Face amount of loan	$ 100,000,000
Redemption price, percentage	105.334%
Senior unsecured notes
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		1,500,000,000
Accreted Balance		1,502,837,000	1,503,759,000
Deferred financing costs, net		(5,990,000)	(8,545,000)
Senior notes, net of deferred finance costs		1,496,847,000	1,495,214,000
Senior unsecured notes | 7.75% Senior unsecured notes maturing on March 15, 2020
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		250,000,000
Accreted Balance		$ 250,000,000	250,000,000
Coupon Rate (as a percent)		7.75%
Initial Term (in Years)		10 years
Senior unsecured notes | 0.98% Senior unsecured notes maturing August 2021
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 350,000,000
Accreted Balance		$ 350,000,000	350,000,000
Coupon Rate (as a percent)		0.98%
Initial Term (in Years)		3 years
Redemption price, percentage		100.00%
Senior unsecured notes | 3.25% Senior unsecured notes maturing October 2022
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 500,000,000
Accreted Balance		$ 499,695,000	499,591,000
Coupon Rate (as a percent)		3.25%
Initial Term (in Years)		5 years
Senior unsecured notes | 4.50% Senior unsecured notes maturing on December 1, 2022
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 300,000,000
Accreted Balance		$ 303,142,000	304,168,000
Coupon Rate (as a percent)		4.50%
Initial Term (in Years)		10 years
Senior unsecured notes | 4.27% Senior unsecured notes maturing on December 17, 2025
Debt disclosures by scheduled maturity date
Unpaid Principal Balance		$ 100,000,000
Accreted Balance		$ 100,000,000	$ 100,000,000
Coupon Rate (as a percent)		4.27%
Initial Term (in Years)		10 years

Corporate Indebtedness - Junior

Corporate Indebtedness - Junior Subordinated Deferrable Interest Debentures and Principal Maturities (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2005	Dec. 31, 2019
Principal Repayments and Joint Venture Debt
2020		$ 468,824,000
2021		601,546,000
2022		1,338,805,000
2023		1,597,301,000
2024		478,781,000
Thereafter		1,066,626,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		$ 5,551,883,000
Trust Preferred Securities
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 100,000,000
Trust Preferred Securities | LIBOR
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)		1.25%
Joint venture
Principal Repayments and Joint Venture Debt
2020		$ 811,628,000
2021		805,276,000
2022		268,952,000
2023		311,436,000
2024		17,022,000
Thereafter		1,813,821,000
Repayments of principal		4,028,135,000
Joint venture | Mortgages and other loans payable
Scheduled Amortization
2020		11,118,000
2021		11,638,000
2022		9,430,000
2023		7,301,000
2024		6,032,000
Thereafter		3,258,000
Principal Repayments and Joint Venture Debt
2020		207,706,000
2021		239,908,000
2022		529,375,000
2023		50,000,000
2024		272,749,000
Thereafter		863,368,000
Future Amortization of Debt		48,777,000
Repayments of principal		2,163,106,000
Joint venture | Trust Preferred Securities
Principal Repayments and Joint Venture Debt
2020		0
2021		0
2022		0
2023		0
2024		0
Thereafter		100,000,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		100,000,000
Joint venture | Revolving Credit Facility
Principal Repayments and Joint Venture Debt
2020		0
2021		0
2022		0
2023		240,000,000
2024		0
Thereafter		0
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		240,000,000
Joint venture | Unsecured Term Loans
Principal Repayments and Joint Venture Debt
2020		0
2021		0
2022		0
2023		1,300,000,000
2024		200,000,000
Thereafter		0
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		1,500,000,000
Joint venture | Senior Unsecured Notes
Principal Repayments and Joint Venture Debt
2020		250,000,000
2021		350,000,000
2022		800,000,000
2023		0
2024		0
Thereafter		100,000,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		$ 1,500,000,000

Corporate Indebtedness - Schedu

Corporate Indebtedness - Schedule of Consolidated Interest Expense, Excluding Capitalized Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest expense
Interest expense before capitalized interest	$ 246,848	$ 236,719	$ 281,551
Interest on financing leases	3,243	8,069	3,098
Interest capitalized	(55,446)	(34,162)	(26,020)
Interest income	(4,124)	(1,957)	(1,584)
Interest expense, net	$ 190,521	$ 208,669	$ 257,045

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Operating expenses, paid to related parties		$ 18,106	$ 17,823	$ 21,400
Amounts due from/to related parties
Due from joint ventures		9,352	18,655
Other		11,769	9,378
Related party receivables		21,121	28,033
Alliance Building Services | Affiliated Entity
Related Party Transaction [Line Items]
Profit participation from related party		3,900	3,900	3,900
Operating expenses, paid to related parties		18,800	18,800	22,600
Stephen L Green Interest | Affiliated Entity
Related Party Transaction [Line Items]
Property management fees from related party		$ 600	$ 600	$ 500
Marc Holliday, Chairman And CEO | One Vanderbilt | Affiliated Entity
Related Party Transaction [Line Items]
Due from (to) related party	$ 1,400
Marc Holliday, Chairman And CEO | One Vanderbilt | Minimum | Affiliated Entity
Related Party Transaction [Line Items]
Percentage of profits due to investors	150.00%
Marc Holliday, Chairman And CEO | One Vanderbilt | Maximum | Affiliated Entity
Related Party Transaction [Line Items]
Percentage of profits due to investors	180.00%
Andrew Mathias, President | One Vanderbilt | Affiliated Entity
Related Party Transaction [Line Items]
Due from (to) related party	$ 1,000
Andrew Mathias, President | One Vanderbilt | Minimum | Affiliated Entity
Related Party Transaction [Line Items]
Percentage of profits due to investors	100.00%
Andrew Mathias, President | One Vanderbilt | Maximum | Affiliated Entity
Related Party Transaction [Line Items]
Percentage of profits due to investors	120.00%
Holiday And Mathias | One Vanderbilt | Affiliated Entity
Related Party Transaction [Line Items]
Stabilization of property, within three years after stabilization, percent		5000.00%
Stabilization of property, three years or more after stabilization, percent		10000.00%
Stabilization of property, anniversary period		7 years

Noncontrolling Interests on t_3

Noncontrolling Interests on the Company's Consolidated Financial Statements - Additional Information (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)shares$ / shares	Dec. 31, 2018USD ($)unit	Dec. 31, 2017USD ($)
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $	$ 387,805
Distributions | $	(478)	$ (8,364)	$ (52,446)
Redemption of common units | $	(25,845)
Net income | $	13,301	12,216	3,995
Accumulated other comprehensive income allocation | $	(2,276)	(66)	(94)
Balance at end of period | $	$ 409,862	387,805
Number of company common stock issued on conversion of Series B preferred units	6.71348
Series B Preferred Stock
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred units, issued (in shares) | shares	0
SL Green Operating Partnership
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $	$ 387,805	461,954
Distributions | $	(14,729)	(15,000)
Issuance of common units | $	19,403	23,655
Redemption of common units | $	(27,962)	(60,718)
Net income | $	13,301	12,216
Accumulated other comprehensive income allocation | $	(2,276)	(66)
Fair value adjustment | $	34,320	(34,236)
Balance at end of period | $	$ 409,862	$ 387,805	461,954
SL Green Operating Partnership
Organization
Noncontrolling interest in the operating partnership (as a percent)	5.03%	4.70%
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares)	4,195,875	4,130,579
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	4,195,875
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Distributions | $	$ (478)	$ (8,364)	(52,446)
Redemption of common units | $	(25,845)
Accumulated other comprehensive income allocation | $	$ (2,276)	$ (66)	$ (94)
SL Green Operating Partnership | Series G Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	1,902,000
Number of preferred units issued (in shares) | shares	1,902,000
Annual dividends on preferred units (in dollars per share)	$ 1.1250
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 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
Preferred Units, shares authorized (in shares) | shares	60
Number of preferred units issued (in shares) | shares	60
Annual dividends on preferred units (in dollars per share)	$ 70
Liquidation preference of preferred units (in dollars per share)	1,000
Conversion Price Per Unit (in dollars per share)	$ 29.12
SL Green Operating Partnership | Series K Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	700,000
Number of preferred units issued (in shares) | shares	563,954
Annual dividends on preferred units (in dollars per share)	$ 0.8750
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 134.67
SL Green Operating Partnership | Series L Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	500,000
Number of preferred units issued (in shares) | shares	378,634
Annual dividends on preferred units (in dollars per share)	$ 1
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series M Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	1,600,000
Number of preferred units issued (in shares) | shares	1,600,000
Annual dividends on preferred units (in dollars per share)	$ 0.9375
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series N Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	552,303
Number of preferred units issued (in shares) | shares	552,303
Annual dividends on preferred units (in dollars per share)	$ 0.7500
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series O Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	1
Number of preferred units issued (in shares) | shares	1
Annual dividends on preferred units (in dollars per share)	$ (6)
Liquidation preference of preferred units (in dollars per share)	(6)
Conversion Price Per Unit (in dollars per share)	$ 0
Preferred stock, dividend, multiplier per common unit distribution	1,350
SL Green Operating Partnership | Series P Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	200,000
Number of preferred units issued (in shares) | shares	200,000
Annual dividends on preferred units (in dollars per share)	$ 1
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series Q Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	268,000
Number of preferred units issued (in shares) | shares	268,000
Annual dividends on preferred units (in dollars per share)	$ 0.8750
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 148.95
SL Green Operating Partnership | Series R Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	400,000
Number of preferred units issued (in shares) | shares	400,000
Annual dividends on preferred units (in dollars per share)	$ 0.8750
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 154.89
SL Green Operating Partnership | Series S Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	1,077,280
Number of preferred units issued (in shares) | shares	1,077,280
Annual dividends on preferred units (in dollars per share)	$ 1
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series T Preferred Stock
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	230,000
Number of preferred units issued (in shares) | shares	230,000
Annual dividends on preferred units (in dollars per share)	$ 0.6875
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 119.02
SL Green Operating Partnership | Series U Preferred Stock
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	680,000
Number of preferred units issued (in shares) | shares	680,000
Annual dividends on preferred units (in dollars per share)	$ 1.1250
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series A Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	109,161
Number of preferred units issued (in shares) | shares	109,161
Annual dividends on preferred units (in dollars per share)	$ 35
Liquidation preference of preferred units (in dollars per share)	1,000
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series V Preferred Stock
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	40,000
Number of preferred units issued (in shares) | shares	40,000
Annual dividends on preferred units (in dollars per share)	$ 0.8750
Liquidation preference of preferred units (in dollars per share)	25
Conversion Price Per Unit (in dollars per share)	0
Minimum | SL Green Operating Partnership | Series A Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	$ 0.75

Noncontrolling Interests on t_4

Noncontrolling Interests on the Company's Consolidated Financial Statements - Preferred Unit Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units	$ (25,845)
SL Green Operating Partnership
Rollforward Analysis of Preferred Unit Activity
Issuance of preferred units	19,403	$ 23,655
Redemption of preferred units	(27,962)	(60,718)
SL Green Operating Partnership | Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period	300,427	301,735
Issuance of preferred units	1,000	0
Redemption of preferred units	(18,142)	(1,308)
Balance at end of period	$ 283,285	$ 300,427

Stockholders' Equity of the C_3

Stockholders' Equity of the Company - Additional Information (Details) - $ / shares	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Authorized capital stock (in shares)	260,000,000
Authorized shares, par value (in dollars per share)	$ 0.01
Common stock, shares authorized (in shares)	160,000,000	160,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Excess stock, shares authorized (shares)	75,000,000
Excess stock, par value (in dollars per share)	$ 0.01
Preferred stock, shares authorized (shares)	25,000,000
Preferred stock, par (in dollars per share)	$ 0.01
Excess shares issued (shares)	0
Common Stock
Class of Stock [Line Items]
Shares, outstanding (in shares)	79,202,000	83,684,000	92,803,000	100,562,000
Common Stock | SL Green Operating Partnership
Class of Stock [Line Items]
Shares, outstanding (in shares)	79,202,322

Stockholders' Equity of the C_4

Stockholders' Equity of the Company - Stock Repurchase Program (Details)	12 Months Ended
	Dec. 31, 2019USD ($)increase$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Jun. 30, 2018USD ($)	Aug. 31, 2016USD ($)
Class of Stock [Line Items]
Number of shares purchased (in shares) | shares	4,596,171	9,744,911	8,342,411
Maximum approximate dollar value of shares that may yet be purchased under the plan | $ / shares	$ 83.62	$ 96.22	$ 101.64
2016 Repurchase Program
Class of 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	4
Stock repurchase program, authorized amount, total | $	$ 3,000,000,000
Number of shares purchased (in shares) | shares	22,683,493	18,087,322	8,342,411

Stockholders' Equity of the C_5

Stockholders' Equity of the Company - At-the-Market Equity Offering Program and Perpetual Preferred Stock (Details) - USD ($)	1 Months Ended	12 Months Ended
	Aug. 31, 2012	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2015
2015 ATM Equity Offering Program
Stockholders' Equity
Aggregate value of the shares of common stock to be sold				$ 300,000,000
Series I Preferred Stock
Stockholders' Equity
Preferred stock, shares outstanding (in shares)	9,200,000	9,200,000	9,200,000
Dividend rate preferred units (as a percent)	6.50%	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	$ 221,900,000

Stockholders' Equity of the C_6

Stockholders' Equity of the Company - Schedule of Common Stock Issued and Proceeds Received Dividend Reinvestments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Feb. 28, 2018
Stockholders' Equity
Common stock, shares authorized (in shares)	160,000,000	160,000,000
Dividend Reinvestment and Stock Purchase Plan (DRIP)
Stockholders' Equity
Common stock, shares authorized (in shares)				3,500,000
Issuance of common stock (in shares)	3,867	1,399	2,141
Dividend reinvestments/stock purchases under the DRSPP	$ 334	$ 136	$ 223

Stockholders' Equity of the C_7

Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic Earnings:
Income attributable to SL Green common stockholders	$ 17,432	$ 33,157	$ 161,103	$ 43,792	$ (61,219)	$ 88,209	$ 103,556	$ 101,766	$ 255,484	$ 232,312	$ 86,424
Net income attributable to SL Green common stockholders (numerator for basic earnings per share)									253,745	231,760	85,953
Effect of Dilutive Securities:
Add back: Dilutive effect of earnings allocated to participating securities									1,719	552	471
Add back: Effect of dilutive securities (redemption of units to common shares)									13,301	12,216	3,995
Diluted Earnings:
Income attributable to SL Green common stockholders (numerator for diluted earnings per share)									$ 268,765	$ 244,528	$ 90,419
Basic Shares:
Weighted average common stock outstanding (in shares)									81,733,000	86,753,000	98,571,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (in shares)									4,275,000	4,562,000	4,556,000
Stock-based compensation plans (in shares)									554,000	215,000	276,000
Diluted weighted average common stock outstanding (in shares)									86,562,000	91,530,000	103,403,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,252,670	1,138,647	774,782

Partners' Capital of the Oper_3

Partners' Capital of the Operating Partnership - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019shares	Dec. 31, 2018unitshares	Dec. 31, 2017shares	Dec. 31, 2016shares
Common Stock
Stockholders' Equity
Units, outstanding	79,202,000	83,684,000	92,803,000	100,562,000
SL Green Operating Partnership
Stockholders' Equity
Noncontrolling interest in the operating partnership (as a percent)	5.03%	4.70%
Number of units of operating partnership owned by the noncontrolling interest unit holders (units)	4,195,875	4,130,579
SL Green Operating Partnership | Series I Preferred Units
Stockholders' Equity
Units, outstanding	9,200,000
Common units redemption, period of restriction	1 year
Conversion of stock, shares issued (in shares)	1
SL Green Operating Partnership | Common Stock
Stockholders' Equity
Units, outstanding	79,202,322

Partners' Capital of the Oper_4

Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator
Net income attributable to SL Green common stockholders (numerator for basic earnings per share)									$ 253,745	$ 231,760	$ 85,953
Add back: Dilutive effect of earnings allocated to participating securities									$ 1,719	$ 552	$ 471
Denominator
Weighted average common stock outstanding (in shares)									81,733,000	86,753,000	98,571,000
Diluted weighted average common stock outstanding (in shares)									86,562,000	91,530,000	103,403,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,252,670	1,138,647	774,782
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 18,426	$ 34,876	$ 169,413	$ 46,070	$ (64,658)	$ 93,006	$ 109,142	$ 107,038	$ 268,785	$ 244,528	$ 90,419
Less: distributed earnings allocated to participating securities									(1,739)	(552)	(471)
Net income attributable to SL Green common stockholders (numerator for basic earnings per share)									267,046	243,976	89,948
Add back: Dilutive effect of earnings allocated to participating securities									1,719	$ 552	$ 471
Income attributable to SLGOP common unitholders									$ 268,765
Denominator
Weighted average common stock outstanding (in shares)									86,008,000	91,315,000	103,127,000
Stock-based compensation plans (shares)									554,000	215,000	276,000
Diluted weighted average common stock outstanding (in shares)									86,562,000	91,530,000	103,403,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,252,670	1,138,647	774,782

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Details)	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2014shares	Dec. 31, 2019USD ($)unit / sharesfungible_unitshares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016shares
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				$ 2,100,000	$ 6,300,000	$ 7,200,000
Stock options, stock appreciation rights and other awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of option (in years)				5 years
All other awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fungible units per share (in fungible units per share) | unit / shares				1
Expected life of option (in years)				10 years
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of option (in years)				0 days	3 years 6 months	4 years 4 months 24 days
Period of commencement of option vesting, from date of grant (in years)				1 year
Remaining weighted average contractual life of the options outstanding (in years)				2 years 8 months 12 days
Remaining weighted average contractual life of the options exercisable (in years)				2 years 8 months 12 days
Total unrecognized compensation cost related to unvested stock awards				$ 100,000
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)				2 months 12 days
Weighted average fair value of options granted during the period				$ 0	$ 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
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual award vesting rate, low end of range (as a percent)				15.00%
Annual award vesting rate, high end of range (as a percent)				35.00%
Class O LTIP Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred unit distributions as a percentage of common unit distributions				10.00%
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense				$ 12,892,249	12,757,704	9,809,749
Total unrecognized compensation cost related to unvested stock awards				$ 20,800,000
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)				2 years
Fair value of restricted stock vested during the period				$ 12,100,000	9,800,000	9,400,000
Weighted average fair value of options granted during the period				$ 11,131,181	$ 13,440,503	$ 9,905,986
Awards granted (in shares) | shares				126,350	162,900	96,185
Awards outstanding (in shares) | shares				3,566,466	3,452,016	3,298,216	3,202,031
LTIP units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for recognition of compensation cost related to unvested stock awards (in years)				2 years 3 months 18 days
Weighted average fair value of options granted during the period				$ 58,300,000	$ 22,000,000
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost related to unvested stock awards				31,200,000
Share-based Payment Arrangement, Noncash Expense				$ 22,200,000	24,400,000	$ 26,100,000
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for issuance (shares) | shares				500,000
Shares of common stock available for issuance (shares)				85.00%
Duration of each offering period starting the first day of each calendar quarter (in months)				3 months
Shares of common stock issued (shares) | shares				131,440
Fourth Amended and Restated 2003 Stock Option and Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum fungible units that may be granted (in shares) | fungible_unit				27,030,000
Fungible units per share (in fungible units per share) | unit / shares				3.74
Shares that may be issued if equal to fungible units (shares) (less than) | shares				27,030,000
Fungible units | fungible_unit				4,100,000
Stock options, stock appreciation rights and other awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fungible units per share (in fungible units per share) | unit / shares				0.73
Third Amendment and Restated 2005 Stock Option and Incentive Plan | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense				$ 2,500,000	$ 5,400,000	7,800,000
2014 Outperformance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense				0		$ 13,600,000
Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options				27,900,000
Maximum award to be earned, if performance reaches maximum threshold, first performance period			0.333
Maximum award to be earned, if performance reaches maximum threshold, first performance period			0.667
Award period (in years)			3 years
Awards granted (in shares) | shares			610,000
2014 Outperformance Plan | Vesting on August 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of units vested		50.00%
2014 Outperformance Plan | Vesting on August 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of units vested	50.00%
Deferred Stock Compensation Plan for Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense				$ 2,400,000
Maximum percentage of the annual retainer fee, chairman fees and meeting fees that may be deferred by non-employee directors (percent)				100.00%
Awards granted (in shares) | shares				18,669
Shares issued (in shares) | shares				9,949
Awards outstanding (in shares) | shares				128,946

Share-based Compensation - Acti

Share-based Compensation - Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	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)	0 days	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 year (in shares)	1,137,017	1,548,719	1,737,213
Granted (in shares)	0	6,000	174,000
Exercised (in shares)	0	(316,302)	(292,193)
Lapsed or cancelled (in shares)	(99,949)	(101,400)	(70,301)
Balance at end of period (in shares)	1,037,068	1,137,017	1,548,719
Options exercisable at end of period (in shares)	914,929	783,035	800,902
Weighted average fair value of options granted during the period	$ 0	$ 84,068	$ 3,816,652
Weighted Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 103.54	$ 101.48	$ 98.44
Granted (in dollars per share)	0	97.91	105.66
Exercised (in dollars per share)	0	90.22	81.07
Lapsed or cancelled (in dollars per share)	115.81	113.22	121.68
Balance at end of period (in dollars per share)	102.36	103.54	101.48
Options exercisable at end of period (in dollars per share)	$ 101.69	$ 101.28	$ 94.33
Restricted Stock Awards
Options Outstanding
Weighted average fair value of options granted during the period	$ 11,131,181	$ 13,440,503	$ 9,905,986
Summary of restricted stock
Balance at beginning of year (in shares)	3,452,016	3,298,216	3,202,031
Granted (in shares)	126,350	162,900	96,185
Cancelled (in shares)	(11,900)	(9,100)	0
Balance at end of period (in shares)	3,566,466	3,452,016	3,298,216
Vested during the period (in shares)	113,259	92,114	95,736
Compensation expense recorded	$ 12,892,249	$ 12,757,704	$ 9,809,749

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 5,517,198	$ 5,947,855	$ 6,589,454	$ 5,517,198	$ 5,947,855	$ 7,750,911
Other comprehensive (loss) income before reclassifications	(43,495)	(2,304)	(2,733)
Amounts reclassified from accumulated other comprehensive loss	(98)	(1,192)	(800)
Ending Balance	5,517,198	5,947,855	6,589,454
Deferred net losses from terminated hedges				(700)	1,300
Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(22,780)	9,716	12,542	(22,780)	9,716	12,596
Other comprehensive (loss) income before reclassifications	(32,723)	(2,252)	(1,618)
Amounts reclassified from accumulated other comprehensive loss	227	(574)	1,564
Ending Balance	(22,780)	9,716	12,542
Net unrealized gain on marketable securities
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,277	1,093	1,042	2,277	1,093	5,520
Other comprehensive (loss) income before reclassifications	1,184	51	(1,348)
Amounts reclassified from accumulated other comprehensive loss	0	0	(3,130)
Ending Balance	2,277	1,093	1,042
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(28,485)	15,108	18,604	(28,485)	15,108	22,137
Ending Balance	(28,485)	15,108	18,604
Joint venture | Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(7,982)	4,299	5,020	$ (7,982)	$ 4,299	$ 4,021
Other comprehensive (loss) income before reclassifications	(11,956)	(103)	233
Amounts reclassified from accumulated other comprehensive loss	(325)	(618)	766
Ending Balance	$ (7,982)	$ 4,299	$ 5,020

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	May 31, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value of Financial Instruments
Marketable securities		$ 29,887				$ 28,638				$ 29,887	$ 28,638
Interest rate cap and swap agreements (included in other assets)		4,419				18,676				4,419	18,676
Asset impairment loss											221,900
Purchase price and other fair value adjustment		0	$ 3,799	$ 67,631	$ (2,041)	0	$ (3,057)	$ 11,149	$ 49,293	69,389	57,385	$ 0
Debt and preferred equity investments		1,580,306				2,099,393				1,580,306	2,099,393
Carrying Value
Fair Value of Financial Instruments
Fixed rate debt		3,536,286				3,543,476				3,536,286	3,543,476
Variable rate debt		2,018,434				2,048,442				2,018,434	2,048,442
Total		5,554,720				5,591,918				5,554,720	5,591,918
Fair Value
Fair Value of Financial Instruments
Marketable securities		29,887				28,638				29,887	28,638
Total		5,661,484				5,288,093				5,661,484	5,288,093
Estimated fair value of debt and preferred equity investments, low end of range		1,600,000				2,100,000				1,600,000	2,100,000
Estimated fair value of debt and preferred equity investments, high end of range		1,700,000				2,300,000				1,700,000	2,300,000
Level 1
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in other assets)		0				0				0	0
Level 2
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in other assets)		4,419				18,676				4,419	18,676
Level 3
Fair Value of Financial Instruments
Marketable securities		0				0				0	0
Interest rate cap and swap agreements (included in other assets)		0				0				0	0
Level 3 | Carrying Value
Fair Value of Financial Instruments
Debt and preferred equity investments						2,099,393					2,099,393
Level 3 | Fair Value
Fair Value of Financial Instruments
Fixed rate debt		3,642,770				3,230,127				3,642,770	3,230,127
Variable rate debt		2,018,714				2,057,966				2,018,714	2,057,966
Equity marketable securities | Level 1
Fair Value of Financial Instruments
Marketable securities		0				0				0	0
Mortgage-backed securities
Fair Value of Financial Instruments
Marketable securities		29,887				28,638				29,887	28,638
Mortgage-backed securities | Level 2
Fair Value of Financial Instruments
Marketable securities		29,887				28,638				29,887	28,638
Total Fixed Rate | Mortgage and Jr Mortgage Loan with an Initial Maturity Date of April 2017
Fair Value of Financial Instruments
Notes receivable	$ 250,500
Interest receivable	7,700
2 Herald Square
Fair Value of Financial Instruments
Purchase price fair value adjustment	$ 8,100
Joint venture
Fair Value of Financial Instruments
Debt and preferred equity investments		0				44,357				0	44,357
Joint venture | 919 Third Avenue | 919 Third Avenue
Fair Value of Financial Instruments
Purchase price and other fair value adjustment										49,300
Accrued Interest Payable and Other
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		29,110				7,663				29,110	7,663
Accrued Interest Payable and Other | Level 1
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		0				0				0	0
Accrued Interest Payable and Other | Level 2
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		29,110				7,663				29,110	7,663
Accrued Interest Payable and Other | Level 3
Fair Value of Financial Instruments
Interest rate cap and swap agreements (included in accrued interest payable and other liabilities)		$ 0				$ 0				$ 0	$ 0

Financial Instruments_ Deriva_3

Financial Instruments: Derivatives and Hedging (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financial Instruments: Derivatives and Hedging
Fair Value	$ 4,419	$ 18,676
Gain (loss) from changes in fair value	100	200	$ 500
Fair value of derivatives in a net liability position	29,500
Aggregate termination value	30,100
Amount of Loss Recognized in Other Comprehensive Loss	(44,229)	(4,072)	(2,482)
Amount of (Loss) Gain Reclassified from Accumulated Other Comprehensive Loss into Income	(5)	2,265	2,796
Interest Rate Swap Expiring May 2020
Financial Instruments: Derivatives and Hedging
Notional Value	$ 300,000
Strike Rate	3.75%
Fair Value	$ 0
Interest Rate Swap Expiring November 2020
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000
Strike Rate	1.928%
Fair Value	$ (281)
Interest Rate Swap Expiring November 2020, 2
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000
Strike Rate	1.934%
Fair Value	$ (286)
Interest Rate Swap Expiring December 2020
Financial Instruments: Derivatives and Hedging
Notional Value	$ 111,869
Strike Rate	3.50%
Fair Value	$ 0
Interest Rate Swap Expiring March 2021
Financial Instruments: Derivatives and Hedging
Notional Value	$ 85,000
Strike Rate	4.00%
Fair Value	$ 0
Interest Rate Swap Expiring in July 2023
Financial Instruments: Derivatives and Hedging
Notional Value	$ 200,000
Strike Rate	1.131%
Fair Value	$ 3,015
Interest Rate Swap Expiring in July 2023, 2
Financial Instruments: Derivatives and Hedging
Notional Value	$ 100,000
Strike Rate	1.161%
Fair Value	$ 1,404
Interest Rate Swap Expiring January 2024
Financial Instruments: Derivatives and Hedging
Notional Value	$ 150,000
Strike Rate	2.696%
Fair Value	$ (6,570)
Interest Rate Swap Expiring January 2026
Financial Instruments: Derivatives and Hedging
Notional Value	$ 150,000
Strike Rate	2.721%
Fair Value	$ (9,344)
Interest Rate Swap Expiring January 2026, 2
Financial Instruments: Derivatives and Hedging
Notional Value	$ 200,000
Strike Rate	2.74%
Fair Value	$ (12,629)
Interest Rate Swap
Financial Instruments: Derivatives and Hedging
Fair Value	(24,691)
Amount of Loss Recognized in Other Comprehensive Loss	(33,907)	(2,284)	(2,282)
Amount of (Loss) Gain Reclassified from Accumulated Other Comprehensive Loss into Income	(261)	1,168	1,816
Interest Expense
Financial Instruments: Derivatives and Hedging
Estimated current balance held in accumulated other comprehensive loss to be reclassified into earnings within the next 12 months	400
Income Loss From Equity Method Investments
Financial Instruments: Derivatives and Hedging
Estimated current balance held in accumulated other comprehensive loss to be reclassified into earnings within the next 12 months	(100)
Joint venture
Financial Instruments: Derivatives and Hedging
Amount of Loss Recognized in Other Comprehensive Loss	(10,322)	(1,788)	(200)
Amount of (Loss) Gain Reclassified from Accumulated Other Comprehensive Loss into Income	$ 256	$ 1,097	$ 980

Rental Income - Future Minimum

Rental Income - Future Minimum Rents (Details) $ in Thousands	Dec. 31, 2019USD ($)
Lessor, Lease, Description [Line Items]
Total payments to be received	$ 1,600,000
Consolidated properties
Lessor, Lease, Description [Line Items]
2020	799,001
2021	651,815
2022	600,912
2023	536,835
2024	496,476
Thereafter	2,938,340
Total payments to be received	6,023,379
Unconsolidated properties
Lessor, Lease, Description [Line Items]
2020	390,725
2021	397,524
2022	380,598
2023	354,621
2024	325,459
Thereafter	1,986,928
Total payments to be received	$ 3,835,855

Rental Income - Future Minimu_2

Rental Income - Future Minimum Rental Payment Prior to Adoption (Details) $ in Thousands	Dec. 31, 2018USD ($)
Consolidated properties
2019	$ 830,336
2020	765,610
2021	625,956
2022	562,250
2023	500,499
Thereafter	3,272,014
Total future minimum payments receivable	6,556,665
Unconsolidated Properties
2019	348,060
2020	375,228
2021	380,886
2022	348,222
2023	333,501
Thereafter	2,098,995
Total future minimum payments receivable	$ 3,884,892

Rental Income - Lease Income (D

Rental Income - Lease Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Fixed lease payments	$ 858,587	$ 858,160
Variable lease payments	120,496	113,596
Total lease payments	979,083	971,756
Amortization of acquired above and below-market leases	4,474	6,818
Total rental revenue	$ 983,557	$ 978,574

Benefit Plans (Details)

Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended					24 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Jun. 30, 2019
Multiemployer Plans [Line Items]
Plan contributions	$ 14,160	$ 13,433		$ 16,745
401 (K) Plan
Employee contribution limit per calendar year	15.00%
Employer matching contribution, percent of match	100.00%	100.00%		50.00%
Percentage of eligible compensation matched by employer	4.00%	4.00%		6.00%
Matching contribution	$ 1,600	$ 1,100		$ 1,000
Health Plan
Multiemployer Plans [Line Items]
Plan contributions	$ 9,949	9,310		11,426
Multiemployer plan, contributions by employer			$ 1,400,000		$ 1,300,000	$ 1,500,000
Percentage of contributions required for multiple collective-bargaining arrangements	5.00%
Other plans
Multiemployer Plans [Line Items]
Plan contributions	$ 1,108	1,106		1,463
Pension Plan
Multiemployer Plans [Line Items]
Multiemployer plans, surcharge	No
Plan contributions	$ 3,103	$ 3,017	$ 272,300	$ 3,856	$ 257,800	$ 290,100
Multiemployer plans, contributions by employer, percent	5.00%

Commitments and Contingencies_2

Commitments and Contingencies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Commitments [Line Items]
Employment agreements with certain executives, minimum cash-based compensation for next fiscal year	$ 3,300,000
Initial term of non cancellable operating leases, minimum (in years)	1 year
Financing leases
2020	$ 2,619,000
2021	2,794,000
2022	2,794,000
2023	2,794,000
2024	2,819,000
Thereafter	814,283,000
Total minimum lease payments	828,103,000
Amount representing interest	(783,655,000)
Lease liability - financing leases	44,448,000	$ 43,616,000
Non-cancellable operating leases
2020	31,508,000
2021	31,702,000
2022	29,548,000
2023	27,243,000
2024	27,263,000
Thereafter	649,289,000
Total minimum lease payments	796,553,000
Amount discounted using incremental borrowing rate	(414,882,000)
Lease liability - operating leases	381,671,000	3,603,000
Minimum sublease rentals to be received in the future	1,600,000,000
Finance lease cost	4,500,000
Finance lease, interest expense	3,243,000	8,069,000	$ 3,098,000
Finance lease, right-of-use asset, amortization	1,200,000
Operating lease, cost	$ 33,188,000	32,965,000	$ 33,231,000
Operating lease, weighted average discount rate, percent	8.49%
Operating lease, weighted average remaining lease term	67 years
711 Third Avenue
Other Commitments [Line Items]
Ownership percentage	50.00%
Belmont
Other Commitments [Line Items]
Loss reserves	$ 2,900,000	$ 4,000,000
Ticonderoga
Other Commitments [Line Items]
Loss reserves	$ 0

Segment Information - Additiona

Segment Information - Additional Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)segment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Segment information
Number of reportable segments (segment) | segment									2
Total revenues	$ 308,082	$ 313,634	$ 313,024	$ 304,255	$ 317,036	$ 307,545	$ 301,116	$ 301,695	$ 1,238,995	$ 1,227,392	$ 1,511,473
Net Income									291,487	270,856	101,069
Total assets	12,766,320				12,751,358				12,766,320	12,751,358
Marketing, general and administrative									100,875	92,631	100,498
Operating Segments | Real Estate Segment
Segment information
Total revenues									1,043,405	1,025,900	1,317,602
Net Income									158,972	129,253	(69,294)
Total assets	11,063,155				10,481,594				11,063,155	10,481,594
Operating Segments | Debt and Preferred Equity Segment
Segment information
Total revenues									195,590	201,492	193,871
Net Income									132,515	141,603	$ 170,363
Total assets	$ 1,703,165				$ 2,269,764				$ 1,703,165	$ 2,269,764

Quarterly Financial Data of t_5

Quarterly Financial Data of the Company (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 308,082	$ 313,634	$ 313,024	$ 304,255	$ 317,036	$ 307,545	$ 301,116	$ 301,695	$ 1,238,995	$ 1,227,392	$ 1,511,473
Total expenses	(252,712)	(263,341)	(258,383)	(260,328)	(267,678)	(265,553)	(258,303)	(258,282)	(1,034,764)	(1,049,816)	(1,346,445)
Equity in net income from unconsolidated joint ventures	(11,874)	(9,864)	(7,546)	(5,234)	(2,398)	971	4,702	4,036	(34,518)	7,311	21,892
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	0	0	59,015	17,166	167,445	70,937	72,025	(6,440)	76,181	303,967	16,166
Purchase price and other fair value adjustment	0	3,799	67,631	(2,041)	0	(3,057)	11,149	49,293	69,389	57,385	0
(Loss) gain on sale of real estate, net	(19,241)	3,541	0	(1,049)	(36,984)	(2,504)	(14,790)	23,521	(16,749)	(30,757)	73,241
Depreciable real estate reserves and impairment	0	(7,047)	0	0	(220,852)	(6,691)	0	0	(7,047)	(227,543)	(178,520)
Loss on early extinguishment of debt					(14,889)	(2,194)	0	0	0	(17,083)	0
Noncontrolling interests and preferred unit distributions	(3,086)	(3,827)	(8,901)	(5,239)	838	(7,507)	(8,606)	(8,319)
Net income (loss) attributable to SL Green/SLGOP	21,169	36,895	164,840	47,530	(57,482)	91,947	107,293	105,504	270,434	247,262	101,374
Perpetual preferred stock dividends	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(14,950)	(14,950)	(14,950)
Net income attributable to SL Green common stockholders	$ 17,432	$ 33,157	$ 161,103	$ 43,792	$ (61,219)	$ 88,209	$ 103,556	$ 101,766	$ 255,484	$ 232,312	$ 86,424
Net (loss) income attributable to common stockholders per common share - basic (usd per share)	$ 0.21	$ 0.40	$ 1.94	$ 0.52	$ (0.73)	$ 1.03	$ 1.19	$ 1.12
Net (loss) income attributable to common stockholders per common share - diluted (usd per share)	$ 0.21	$ 0.40	$ 1.94	$ 0.52	$ (0.73)	$ 1.03	$ 1.19	$ 1.12

Quarterly Financial Data of t_6

Quarterly Financial Data of the Operating Partnership (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Total revenues	$ 308,082	$ 313,634	$ 313,024	$ 304,255	$ 317,036	$ 307,545	$ 301,116	$ 301,695	$ 1,238,995	$ 1,227,392	$ 1,511,473
Total expenses	(252,712)	(263,341)	(258,383)	(260,328)	(267,678)	(265,553)	(258,303)	(258,282)	(1,034,764)	(1,049,816)	(1,346,445)
Equity in net (loss) income from unconsolidated joint ventures	(11,874)	(9,864)	(7,546)	(5,234)	(2,398)	971	4,702	4,036	(34,518)	7,311	21,892
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	0	0	59,015	17,166	167,445	70,937	72,025	(6,440)	76,181	303,967	16,166
(Loss) gain on sale of real estate, net	(19,241)	3,541	0	(1,049)	(36,984)	(2,504)	(14,790)	23,521	(16,749)	(30,757)	73,241
Purchase price and other fair value adjustment	0	3,799	67,631	(2,041)	0	(3,057)	11,149	49,293	69,389	57,385	0
Depreciable real estate reserves and impairment	0	(7,047)	0	0	(220,852)	(6,691)	0	0	(7,047)	(227,543)	(178,520)
Gain on sale of investment in marketable securities									0	0	3,262
Loss on early extinguishment of debt					(14,889)	(2,194)	0	0	0	(17,083)	0
Noncontrolling interests and preferred unit distributions	(3,086)	(3,827)	(8,901)	(5,239)	838	(7,507)	(8,606)	(8,319)
Net income (loss) attributable to SL Green/SLGOP	21,169	36,895	164,840	47,530	(57,482)	91,947	107,293	105,504	270,434	247,262	101,374
SL Green Operating Partnership
Condensed Income Statements, Captions [Line Items]
Total revenues	308,082	313,634	313,024	304,255	317,036	307,545	301,116	301,695	1,238,995	1,227,392	1,511,473
Total expenses	(252,713)	(263,341)	(258,383)	(260,328)	(267,678)	(265,553)	(258,303)	(258,282)	(1,034,764)	(1,049,816)	(1,346,445)
Equity in net (loss) income from unconsolidated joint ventures	(11,874)	(9,864)	(7,546)	(5,234)	(2,398)	971	4,702	4,036	(34,518)	7,311	21,892
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	0	0	59,015	17,166	167,445	70,937	72,025	(6,440)	76,181	303,967	16,166
(Loss) gain on sale of real estate, net	(19,241)	3,541	0	(1,049)	(36,984)	(2,504)	(14,790)	23,521	(16,749)	(30,757)	73,241
Purchase price and other fair value adjustment	0	3,799	67,631	(2,041)	0	(3,057)	11,149	49,293	69,389	57,385	0
Depreciable real estate reserves and impairment	0	(7,047)	0	0					(7,047)	(227,543)	(178,520)
Gain on sale of investment in marketable securities					(220,852)	(6,691)	0	0	0	0	3,262
Loss on early extinguishment of debt					(14,889)	(2,194)	0	0	0	(17,083)	0
Noncontrolling interests and preferred unit distributions	(2,091)	(2,108)	(591)	(2,961)	(2,601)	(2,710)	(3,020)	(3,047)	(14,950)	(14,950)	(14,950)
Net income (loss) attributable to SL Green/SLGOP	22,163	38,614	173,150	49,808	(60,921)	96,744	112,879	110,776	283,735	259,478	105,369
Perpetual preferred stock dividends	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)
Net income attributable to SLGOP common unitholders	$ 18,426	$ 34,876	$ 169,413	$ 46,070	$ (64,658)	$ 93,006	$ 109,142	$ 107,038	$ 268,785	$ 244,528	$ 90,419
Net income attributable to common unitholders per common share—basic (in dollars per share)	$ 0.21	$ 0.40	$ 1.94	$ 0.52	$ (0.73)	$ 1.03	$ 1.19	$ 1.12	$ 3.10	$ 2.67	$ 0.87
Net income attributable to common unitholders per common share—diluted (in dollars per share)	$ 0.21	$ 0.40	$ 1.94	$ 0.52	$ (0.73)	$ 1.03	$ 1.19	$ 1.12	$ 3.10	$ 2.67	$ 0.87

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred rent receivable—allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 15,457	$ 17,207	$ 25,203
Additions Charged Against Operations	4,227	491	2,321
Uncollectible Accounts Written-off/Recovery (1)	(7,207)	(2,241)	(10,317)
Balance at End of Year	12,477	15,457	17,207
Tenant and other receivables—allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	15,702	18,637	16,592
Additions Charged Against Operations	2,760	3,726	6,106
Uncollectible Accounts Written-off/Recovery (1)	(6,093)	(6,661)	(4,061)
Balance at End of Year	$ 12,369	$ 15,702	$ 18,637

Schedule III - Real Estate an_2

Schedule III - Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 2,019,700
Initial Cost
Land	1,596,948
Building & Improvements	6,033,164
Cost Capitalized Subsequent To Acquisition
Land	154,596
Building & Improvements	999,859
Gross Amount at Which Carried at Close of Period
Land	1,751,544
Building & Improvements	7,033,023
Total	8,784,567	$ 8,513,935	$ 10,206,122	$ 12,743,332
Accumulated Depreciation	2,060,560	$ 2,099,137	$ 2,300,116	$ 2,264,694
420 Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	299,165
Initial Cost
Land	0
Building & Improvements	333,499
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	192,729
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	526,228
Total	526,228
Accumulated Depreciation	151,898
711 Third Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	19,844
Building & Improvements	115,769
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	59,685
Gross Amount at Which Carried at Close of Period
Land	19,844
Building & Improvements	175,454
Total	195,298
Accumulated Depreciation	52,265
555 W. 57th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	18,846
Building & Improvements	140,946
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	544
Gross Amount at Which Carried at Close of Period
Land	18,846
Building & Improvements	141,490
Total	160,336
Accumulated Depreciation	75,340
461 Fifth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	0
Building & Improvements	88,276
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	19,670
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	107,946
Total	107,946
Accumulated Depreciation	34,535
750 Third Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	51,093
Building & Improvements	251,523
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	3,449
Gross Amount at Which Carried at Close of Period
Land	51,093
Building & Improvements	254,972
Total	306,065
Accumulated Depreciation	109,685
625 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	0
Building & Improvements	291,319
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	14,908
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	306,227
Total	306,227
Accumulated Depreciation	132,531
485 Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	450,000
Initial Cost
Land	78,282
Building & Improvements	452,631
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	6,933
Gross Amount at Which Carried at Close of Period
Land	78,282
Building & Improvements	459,564
Total	537,846
Accumulated Depreciation	197,431
609 Fifth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	53,773
Initial Cost
Land	36,677
Building & Improvements	195,481
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	41,197
Gross Amount at Which Carried at Close of Period
Land	36,677
Building & Improvements	236,678
Total	273,355
Accumulated Depreciation	44,728
810 Seventh Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	114,077
Building & Improvements	550,819
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	(83)
Gross Amount at Which Carried at Close of Period
Land	114,077
Building & Improvements	550,736
Total	664,813
Accumulated Depreciation	190,457
1185 Avenue of the Americas
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	0
Building & Improvements	791,106
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	116,573
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	907,679
Total	907,679
Accumulated Depreciation	292,739
1350 Avenue of the Americas
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	90,941
Building & Improvements	431,517
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	(3,792)
Gross Amount at Which Carried at Close of Period
Land	90,941
Building & Improvements	427,725
Total	518,666
Accumulated Depreciation	142,533
1-6 Landmark Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	100,000
Initial Cost
Land	27,852
Building & Improvements	161,343
Cost Capitalized Subsequent To Acquisition
Land	985
Building & Improvements	8,319
Gross Amount at Which Carried at Close of Period
Land	28,837
Building & Improvements	169,662
Total	198,499
Accumulated Depreciation	84,164
7 Landmark Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	1,721
Building & Improvements	8,417
Cost Capitalized Subsequent To Acquisition
Land	(985)
Building & Improvements	(3,939)
Gross Amount at Which Carried at Close of Period
Land	736
Building & Improvements	4,478
Total	5,214
Accumulated Depreciation	1,657
1055 Washington Boulevard
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	8,386
Building & Improvements	43,242
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	10,545
Gross Amount at Which Carried at Close of Period
Land	8,386
Building & Improvements	53,787
Total	62,173
Accumulated Depreciation	21,723
One Madison Ave
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	173,546
Building & Improvements	672,805
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	22,977
Gross Amount at Which Carried at Close of Period
Land	173,546
Building & Improvements	695,782
Total	869,328
Accumulated Depreciation	210,128
100 Church Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	209,296
Initial Cost
Land	34,994
Building & Improvements	183,932
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	9,181
Gross Amount at Which Carried at Close of Period
Land	34,994
Building & Improvements	193,113
Total	228,107
Accumulated Depreciation	60,198
125 Park Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	120,900
Building & Improvements	270,598
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	6,869
Gross Amount at Which Carried at Close of Period
Land	120,900
Building & Improvements	277,467
Total	398,367
Accumulated Depreciation	88,975
Williamsburg
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	6,200
Building & Improvements	10,158
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	0
Gross Amount at Which Carried at Close of Period
Land	6,200
Building & Improvements	10,158
Total	16,358
Accumulated Depreciation	2,388
110 East 42nd Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	36,196
Building & Improvements	78,353
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	3,247
Gross Amount at Which Carried at Close of Period
Land	36,196
Building & Improvements	81,600
Total	117,796
Accumulated Depreciation	21,124
400 East 58th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	39,094
Initial Cost
Land	17,549
Building & Improvements	38,749
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	373
Gross Amount at Which Carried at Close of Period
Land	17,549
Building & Improvements	39,122
Total	56,671
Accumulated Depreciation	$ 7,091
Interest in property (as a percent)	90.00%
762 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 771
Initial Cost
Land	6,153
Building & Improvements	10,570
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	(35)
Gross Amount at Which Carried at Close of Period
Land	6,153
Building & Improvements	10,535
Total	16,688
Accumulated Depreciation	2,151
304 Park Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	54,489
Building & Improvements	90,643
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	630
Gross Amount at Which Carried at Close of Period
Land	54,489
Building & Improvements	91,273
Total	145,762
Accumulated Depreciation	22,172
635 Sixth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	24,343
Building & Improvements	88,261
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	166
Gross Amount at Which Carried at Close of Period
Land	24,343
Building & Improvements	88,427
Total	112,770
Accumulated Depreciation	14,361
641 Sixth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	45,976
Building & Improvements	77,076
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	141
Gross Amount at Which Carried at Close of Period
Land	45,976
Building & Improvements	77,217
Total	123,193
Accumulated Depreciation	18,564
1080 Amsterdam
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	35,123
Initial Cost
Land	0
Building & Improvements	47,948
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	10,316
Gross Amount at Which Carried at Close of Period
Land	0
Building & Improvements	58,264
Total	58,264
Accumulated Depreciation	$ 6,694
Interest in property (as a percent)	92.50%
315 West 33rd Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 250,000
Initial Cost
Land	195,834
Building & Improvements	179,562
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	2,220
Gross Amount at Which Carried at Close of Period
Land	195,834
Building & Improvements	181,782
Total	377,616
Accumulated Depreciation	30,853
752-760 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	284,286
Building & Improvements	8,314
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	12,660
Gross Amount at Which Carried at Close of Period
Land	284,286
Building & Improvements	20,974
Total	305,260
Accumulated Depreciation	2,752
719 Seventh Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	50,000
Initial Cost
Land	41,180
Building & Improvements	46,232
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	(1,693)
Gross Amount at Which Carried at Close of Period
Land	41,180
Building & Improvements	44,539
Total	85,719
Accumulated Depreciation	$ 1,623
Interest in property (as a percent)	75.00%
110 Greene Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost
Land	45,120
Building & Improvements	228,393
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	2,414
Gross Amount at Which Carried at Close of Period
Land	45,120
Building & Improvements	230,807
Total	275,927
Accumulated Depreciation	31,147
185 Broadway
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	120,110
Initial Cost
Land	45,422
Building & Improvements	27,865
Cost Capitalized Subsequent To Acquisition
Land	118
Building & Improvements	28,282
Gross Amount at Which Carried at Close of Period
Land	45,540
Building & Improvements	56,147
Total	101,687
Accumulated Depreciation	419
30 East 40th Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost
Land	4,652
Building & Improvements	26,654
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	4,238
Gross Amount at Which Carried at Close of Period
Land	4,652
Building & Improvements	30,892
Total	35,544
Accumulated Depreciation	$ 3,267
Interest in property (as a percent)	60.00%
113 Greene Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 15,523
Initial Cost
Land	3,446
Building & Improvements	27,542
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	82
Gross Amount at Which Carried at Close of Period
Land	3,446
Building & Improvements	27,624
Total	31,070
Accumulated Depreciation	827
712 Madison Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	28,000
Initial Cost
Land	7,207
Building & Improvements	47,397
Cost Capitalized Subsequent To Acquisition
Land	0
Building & Improvements	18
Gross Amount at Which Carried at Close of Period
Land	7,207
Building & Improvements	47,415
Total	54,622
Accumulated Depreciation	1,185
106 Spring Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	38,025
Initial Cost
Land	0
Building & Improvements	0
Cost Capitalized Subsequent To Acquisition
Land	14,173
Building & Improvements	66,052
Gross Amount at Which Carried at Close of Period
Land	14,173
Building & Improvements	66,052
Total	80,225
Accumulated Depreciation	1,240
410 Tenth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	330,820
Initial Cost
Land	0
Building & Improvements	0
Cost Capitalized Subsequent To Acquisition
Land	140,307
Building & Improvements	363,523
Gross Amount at Which Carried at Close of Period
Land	140,307
Building & Improvements	363,523
Total	503,830
Accumulated Depreciation	$ (3,175)
Interest in property (as a percent)	70.90%
Other
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost
Land	1,736
Building & Improvements	16,224
Cost Capitalized Subsequent To Acquisition
Land	(2)
Building & Improvements	1,460
Gross Amount at Which Carried at Close of Period
Land	1,734
Building & Improvements	17,684
Total	19,418
Accumulated Depreciation	$ 4,890

Schedule III - Real Estate an_3

Schedule III - Real Estate and Accumulated Depreciation (Activity in Real Estate and Accumulated Depreciation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in real estate
Balance at beginning of year	$ 8,513,935	$ 10,206,122	$ 12,743,332
Property acquisitions	0	52,939	13,323
Improvements	251,674	267,726	342,014
Retirements/disposals/deconsolidation	18,958	(2,012,852)	(2,892,547)
Balance at end of year	8,784,567	8,513,935	10,206,122
Aggregate cost of land, buildings and improvements before depreciation	10,300,000
Changes in accumulated depreciation
Balance at beginning of year	2,099,137	2,300,116	2,264,694
Depreciation for year	222,867	245,033	347,015
Retirements/disposals/deconsolidation	(261,444)	(446,012)	(311,593)
Balance at end of year	$ 2,060,560	$ 2,099,137	$ 2,300,116

Uncategorized Items - a19q4slg1

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