Consolidated Statement of Equity - USD ($) shares in Thousands, $ in Thousands		Total	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjusted Balance	Common Stock	Common Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Additional Paid- In-Capital	Additional Paid- In-Capital Cumulative Effect, Period of Adoption, Adjusted Balance	Treasury Stock	Treasury Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Cumulative Effect, Period of Adoption, Adjusted Balance	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings Cumulative Effect, Period of Adoption, Adjusted Balance	Noncontrolling Interests	Noncontrolling Interests Cumulative Effect, Period of Adoption, Adjusted Balance	Series I Preferred Stock Preferred Stock	Series I Preferred Stock Preferred Stock Cumulative Effect, Period of Adoption, Adjusted Balance
Beginning Balance at Dec. 31, 2017		$ 6,589,454	$ 570,524	$ 7,159,978	$ 939	$ 939	$ 4,968,338	$ 4,968,338	$ (124,049)	$ (124,049)	$ 18,604	$ 18,604	$ 1,139,329	$ 570,524	$ 1,709,853	$ 364,361	$ 364,361	$ 221,932	$ 221,932
Beginning Balance (in shares) at Dec. 31, 2017	[1]				90,172	90,172
Increase (Decrease) in Stockholders' Equity
Net income		247,256											247,262			(6)
Other comprehensive loss		(3,496)									(3,496)
Preferred dividends		(14,950)											(14,950)
DRSPP (in shares)	[1]				1
DRSPP proceeds		136					136
Conversion of units of the Operating Partnership to common stock (in shares)	[1]				155
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)	[1]				145
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings		17,484			$ 1		17,483
Repurchases of common stock (in shares)	[1]				(9,469)
Repurchases of common units		(937,795)			$ (98)		(522,482)						(415,215)
Proceeds from stock options exercised (in shares)	[1]				307
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)
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	[1]				81,311
Increase (Decrease) in Stockholders' Equity
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member
Net income		$ 267,275											270,434			(3,159)
Acquisition of subsidiary interest from noncontrolling interest		(25,845)					(569)									(25,276)
Other comprehensive loss		(43,593)									(43,593)
Preferred dividends		(14,950)											(14,950)
DRSPP (in shares)	[1]				4
DRSPP proceeds		334					334
Conversion of units of the Operating Partnership to common stock (in shares)	[1]				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)	[1]				102
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings		25,763			$ 2		25,761
Repurchases of common stock (in shares)	[1]				(4,466)
Repurchases of common units		(384,399)			$ (46)		(248,287)						(136,066)
Contributions to consolidated joint venture interests		58,462														58,462
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)
Ending Balance at Dec. 31, 2019		5,517,198	$ (39,184)	$ 5,478,014	$ 803	$ 803	4,286,395	$ 4,286,395	(124,049)	$ (124,049)	(28,485)	$ (28,485)	1,084,719	$ (39,184)	$ 1,045,535	75,883	$ 75,883	221,932	$ 221,932
Ending Balance (in shares) at Dec. 31, 2019	[1]				76,956	76,956
Increase (Decrease) in Stockholders' Equity
Net income		385,995											371,055			14,940
Acquisition of subsidiary interest from noncontrolling interest		(1,536)					(3,123)									1,587
Other comprehensive loss		(38,762)									(38,762)
Preferred dividends		(14,950)											(14,950)
DRSPP (in shares)	[1]				17
DRSPP proceeds		1,006					1,006
Conversion of units of the Operating Partnership to common stock (in shares)	[1]				98
Conversion of units in the Operating Partnership to common stock		8,744			$ 1		8,743
Reallocation of noncontrolling interest in the Operating Partnership		32,598											32,598
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)	[1]				(34)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings		25,271			$ 0		25,271
Repurchases of common stock (in shares)	[1]				(8,529)
Repurchases of common units		(532,262)			$ (88)		(455,343)						(76,831)
Contributions to consolidated joint venture interests		12,477														12,477
Distributions to noncontrolling interests		(78,855)														(78,855)
Cash distributions declared ( per common share, none of which represented a return of capital for federal income tax purposes)		(341,945)											(341,945)
Ending Balance at Dec. 31, 2020		$ 4,935,795			$ 716		$ 3,862,949		$ (124,049)		$ (67,247)		$ 1,015,462			$ 26,032		$ 221,932
Ending Balance (in shares) at Dec. 31, 2020	[1]				68,508

[1] On January 21, 2021, we completed a reverse stock split whereby every 1.02918 SL Green common share was combined into 1 SL Green common share. We have retroactively adjusted the outstanding share counts, share activity, cash distributions declared, and earnings per share, as if the reverse split occurred on December 31, 2017.