Accumulated Other Comprehensive Loss of the Operating Partnership (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	$ (6,980)
Ending Balance	(15,821)
Deferred net losses from terminated hedges	10,300	$ 11,800
SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	(7,256)
Other comprehensive loss before reclassifications	(18,360)
Amounts reclassified from accumulated other comprehensive income	9,170
Ending Balance	(16,446)
Deferred net losses from terminated hedges	10,700	$ 12,200
Net unrealized (loss) gain on derivative instruments | SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	(9,845)
Other comprehensive loss before reclassifications	(15,537)
Amounts reclassified from accumulated other comprehensive income	8,221
Ending Balance	(17,161)
Unrealized gain (loss) on marketable securities | SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	2,689
Other comprehensive loss before reclassifications	(337)
Amounts reclassified from accumulated other comprehensive income	0
Ending Balance	2,352
Joint venture | Net unrealized (loss) gain on derivative instruments | SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	(100)
Other comprehensive loss before reclassifications	(2,486)
Amounts reclassified from accumulated other comprehensive income	949
Ending Balance	$ (1,637)