Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	$ (8,749)
Ending Balance	(14,074)
SL Green Realty Corp
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	(8,749)
Other comprehensive loss before reclassifications	(16,088)
Amounts reclassified from accumulated other comprehensive income	10,763
Ending Balance	(14,074)
Deferred net losses from terminated hedges	8,100	$ 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)
Other comprehensive loss before reclassifications	(7,810)
Amounts reclassified from accumulated other comprehensive income	7,862
Ending Balance	(10,108)
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	(869)
Amounts reclassified from accumulated other comprehensive income	0
Ending Balance	1,134
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	(7,409)
Amounts reclassified from accumulated other comprehensive income	2,901
Ending Balance	$ (5,100)