Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	$ 22,137
Ending Balance	16,511
SL Green Realty Corp
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	22,137
Other comprehensive (loss) income before reclassifications	(3,578)
Amounts reclassified from accumulated other comprehensive income	(2,048)
Ending Balance	16,511
Deferred net losses from terminated hedges	4,700	$ 7,100
SL Green Realty Corp | Net unrealized (loss) gain on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	12,596
Other comprehensive (loss) income before reclassifications	(2,429)
Amounts reclassified from accumulated other comprehensive income	758
Ending Balance	10,925
SL Green Realty Corp | Net unrealized gain on marketable securities
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	5,520
Other comprehensive (loss) income before reclassifications	(1,426)
Amounts reclassified from accumulated other comprehensive income	(3,130)
Ending Balance	964
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	4,021
Other comprehensive (loss) income before reclassifications	277
Amounts reclassified from accumulated other comprehensive income	324
Ending Balance	$ 4,622