Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	$ (8,749)
Ending Balance	(16,558)
SL Green Realty Corp
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	(8,749)
Other comprehensive loss before reclassifications	(15,046)
Amounts reclassified from accumulated other comprehensive income	7,237
Ending Balance	(16,558)
Deferred net losses from terminated hedges	8,400	$ 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)
Other comprehensive loss before reclassifications	(7,547)
Amounts reclassified from accumulated other comprehensive income	6,175
Ending Balance	(11,532)
SL Green Realty Corp | Unrealized gain (loss) on marketable securities
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	2,003
Other comprehensive loss before reclassifications	(841)
Amounts reclassified from accumulated other comprehensive income	0
Ending Balance	1,162
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)
Other comprehensive loss before reclassifications	(6,658)
Amounts reclassified from accumulated other comprehensive income	1,062
Ending Balance	$ (6,188)