Consolidated Statements of Capital (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Increase (Decrease) in Partner's Capital
Acquisition of subsidiary interest from noncontrolling interest	$ (1,536)
DRSPP proceeds	166	$ 47
Conversion of common units	84	446
Reallocation of noncontrolling interests in the operating partnership	38,529	(28,932)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	5,502	4,835
Repurchases of common stock	(219,576)	(34,243)
Contribution to consolidated joint venture interests	3,814	161
Cash distributions to noncontrolling interests	$ (492)	$ (208)
Common Stock
Increase (Decrease) in Partner's Capital
DRSPP proceeds (in shares)	2	1
Conversion of common units
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)	(33)	(20)
Repurchases of common stock (in shares)	(2,637)	(398)
Repurchases of common stock	$ (26)	$ (4)
Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Acquisition of subsidiary interest from noncontrolling interest	1,587
Contribution to consolidated joint venture interests	3,814	161
Cash distributions to noncontrolling interests	(492)	(208)
SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Beginning Balance	5,517,198	5,947,855	$ 5,947,855
Net income (loss)	118,246	47,767
Acquisition of subsidiary interest from noncontrolling interest	(1,536)
Other comprehensive loss	(52,383)	(19,113)
Preferred distributions	(3,738)	(3,738)
DRSPP proceeds	166	47
Conversion of common units	84	446
Reallocation of noncontrolling interests in the operating partnership	38,529	(28,932)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	5,502	4,835
Repurchases of common stock	(219,576)	(34,243)
Contribution to consolidated joint venture interests	3,814	161
Cash distributions to noncontrolling interests	(492)	(208)
Cash distributions declared (per common unit, none of which represented a return of capital for federal income tax purposes)	(22,665)	(70,554)
Ending Balance	5,343,965	5,844,323	5,517,198
SL Green Operating Partnership \| Common Stock \| Partners' Interest
Increase (Decrease) in Partner's Capital
Beginning Balance	$ 5,247,868	$ 5,664,481	$ 5,664,481
Beginning Balance (units)	79,202	83,684	83,684
Net income (loss)	$ 118,539	$ 47,530
Acquisition of subsidiary interest from noncontrolling interest	(3,123)
Preferred distributions	$ (3,738)	$ (3,738)
DRSPP proceeds (in shares)	2	1
DRSPP proceeds	$ 166	$ 47
Conversion of common units (in shares)	1	5
Conversion of common units	$ 84	$ 446
Reallocation of noncontrolling interests in the operating partnership	$ 38,529	$ (28,932)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)	(33)	(20)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	$ 5,502	$ 4,835
Repurchases of common stock (in shares)	(2,637)	(398)
Repurchases of common stock	$ (219,576)	$ (34,243)
Cash distributions declared (per common unit, none of which represented a return of capital for federal income tax purposes)	(22,665)	(70,554)
Ending Balance	$ 5,122,402	$ 5,579,872	$ 5,247,868
Ending Balance (units)	76,535	83,272	79,202
SL Green Operating Partnership \| Accumulated Other Comprehensive Loss
Increase (Decrease) in Partner's Capital
Beginning Balance	$ (28,485)	$ 15,108	$ 15,108
Other comprehensive loss	(52,383)	(19,113)
Ending Balance	(80,868)	(4,005)	(28,485)
SL Green Operating Partnership \| Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Beginning Balance	75,883	46,334	46,334
Net income (loss)	(293)	237
Acquisition of subsidiary interest from noncontrolling interest	1,587
Contribution to consolidated joint venture interests	3,814	161
Cash distributions to noncontrolling interests	(492)	(208)
Ending Balance	80,499	46,524	75,883
Series I Preferred Stock \| SL Green Operating Partnership \| Preferred Units
Increase (Decrease) in Partner's Capital
Beginning Balance	221,932	221,932	221,932
Ending Balance	221,932	$ 221,932	221,932
Cumulative Effect, Period Of Adoption, Adjusted Balance \| SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Beginning Balance	5,478,014
Ending Balance			5,478,014
Cumulative Effect, Period Of Adoption, Adjusted Balance \| SL Green Operating Partnership \| Common Stock \| Partners' Interest
Increase (Decrease) in Partner's Capital
Beginning Balance	5,208,684
Ending Balance			5,208,684
Cumulative Effect, Period Of Adoption, Adjusted Balance \| SL Green Operating Partnership \| Accumulated Other Comprehensive Loss
Increase (Decrease) in Partner's Capital
Beginning Balance	(28,485)
Ending Balance			(28,485)
Cumulative Effect, Period Of Adoption, Adjusted Balance \| SL Green Operating Partnership \| Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Beginning Balance	75,883
Ending Balance			75,883
Cumulative Effect, Period Of Adoption, Adjusted Balance \| Series I Preferred Stock \| SL Green Operating Partnership \| Preferred Units
Increase (Decrease) in Partner's Capital
Beginning Balance	221,932
Ending Balance			221,932
Accounting Standards Update 2016-13 \| Cumulative Effect, Period Of Adoption, Adjustment \| SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Beginning Balance	(39,184)
Ending Balance			(39,184)
Accounting Standards Update 2016-13 \| Cumulative Effect, Period Of Adoption, Adjustment \| SL Green Operating Partnership \| Common Stock \| Partners' Interest
Increase (Decrease) in Partner's Capital
Beginning Balance	$ (39,184)
Ending Balance			$ (39,184)

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