Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	$ (8,749)
Ending Balance	22,137	$ (8,749)
SL Green Realty Corp
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	(8,749)	(6,980)	$ (15,211)
Other comprehensive loss before reclassifications	18,211	(13,467)	(421)
Amounts reclassified from accumulated other comprehensive income	12,675	11,698	8,652
Ending Balance	22,137	(8,749)	(6,980)
Deferred net losses from terminated hedges	7,100	9,700
SL Green Realty Corp | Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	(10,160)	(9,498)	(15,125)
Other comprehensive loss before reclassifications	13,534	(11,143)	(576)
Amounts reclassified from accumulated other comprehensive income	9,222	10,481	6,203
Ending Balance	12,596	(10,160)	(9,498)
SL Green Realty Corp | Unrealized gain (loss) on marketable securities
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	2,003	2,613	4,784
Other comprehensive loss before reclassifications	3,517	(610)	(2,692)
Amounts reclassified from accumulated other comprehensive income	0	0	521
Ending Balance	5,520	2,003	2,613
SL Green Realty Corp | Joint venture | Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	(592)	(95)	(4,870)
Other comprehensive loss before reclassifications	1,160	(1,714)	2,847
Amounts reclassified from accumulated other comprehensive income	3,453	1,217	1,928
Ending Balance	$ 4,021	$ (592)	$ (95)