Consolidated Statement of Capital (Unaudited) - USD ($) shares in Thousands, $ in Thousands	6 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Increase (Decrease) in Partner's Capital
DRSPP proceeds	$ 64
Conversion of common units	1,560
Reallocation of noncontrolling interests in the operating partnership	(4,493)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	8,090
Repurchases of common stock	(693,091)
Contribution to consolidated joint venture interests	1,828
Deconsolidation of partially owned entity	(314,596)
Cash distributions to noncontrolling interests	$ (724)
Common Stock
Increase (Decrease) in Partner's Capital
DRSPP proceeds (in shares)	1
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)	(20)
Repurchases of common stock (in shares)	(7,133)
Repurchases of common stock	$ (72)
Contributions - proceeds from stock options exercised (in shares)	59
Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Contribution to consolidated joint venture interests	$ 1,828
Deconsolidation of partially owned entity	(314,596)
Cash distributions to noncontrolling interests	(724)
SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Beginning Balance	6,589,454
Adjusted Balance	7,159,978
Net income	213,168
Other comprehensive income	14,018
Preferred distributions	(7,475)
DRSPP proceeds	64
Conversion of common units	1,560
Reallocation of noncontrolling interests in the operating partnership	(4,493)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	8,090
Repurchases of common stock	(693,091)
Contribution to consolidated joint venture interests	1,828
Deconsolidation of partially owned entity	(314,596)
Contributions - proceeds from stock options exercised	5,637
Cash distributions to noncontrolling interests	(724)
Cash distributions declared ($1.625 per common unit, none of which represented a return of capital for federal income tax purposes)	(141,908)
Ending Balance	6,242,056
SL Green Operating Partnership \| Common Stock \| Partners' Interest
Increase (Decrease) in Partner's Capital
Beginning Balance	$ 5,984,557
Beginning Balance (units)	92,803
Adjusted Balance	$ 6,555,081
Net income	212,797
Preferred distributions	$ (7,475)
DRSPP proceeds (in shares)	1
DRSPP proceeds	$ 64
Conversion of common units (in shares)	15
Conversion of common units	$ 1,560
Reallocation of noncontrolling interests in the operating partnership	$ (4,493)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)	(20)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	$ 8,090
Repurchases of common stock (in shares)	(7,133)
Repurchases of common stock	$ (693,091)
Contributions - proceeds from stock options exercised (in shares)	59
Contributions - proceeds from stock options exercised	$ 5,637
Cash distributions declared ($1.625 per common unit, none of which represented a return of capital for federal income tax purposes)	(141,908)
Ending Balance	$ 5,936,262
Ending Balance (units)	85,725
SL Green Operating Partnership \| Accumulated Other Comprehensive Income
Increase (Decrease) in Partner's Capital
Beginning Balance	$ 18,604
Adjusted Balance	18,604
Other comprehensive income	14,018
Ending Balance	32,622
SL Green Operating Partnership \| Noncontrolling Interests
Increase (Decrease) in Partner's Capital
Beginning Balance	364,361
Adjusted Balance	364,361
Net income	371
Contribution to consolidated joint venture interests	1,828
Deconsolidation of partially owned entity	(314,596)
Cash distributions to noncontrolling interests	(724)
Ending Balance	51,240
Series I Preferred Stock \| SL Green Operating Partnership \| Preferred Units
Increase (Decrease) in Partner's Capital
Beginning Balance	221,932
Adjusted Balance	221,932
Ending Balance	$ 221,932
Accounting Standards Update 2014-09
Increase (Decrease) in Partner's Capital
Cumulative adjustment upon adoption of ASC 610-20		$ 570,524
Accounting Standards Update 2014-09 \| SL Green Operating Partnership
Increase (Decrease) in Partner's Capital
Cumulative adjustment upon adoption of ASC 610-20		570,524
Accounting Standards Update 2014-09 \| SL Green Operating Partnership \| Common Stock \| Partners' Interest
Increase (Decrease) in Partner's Capital
Cumulative adjustment upon adoption of ASC 610-20		$ 570,524

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