Accumulated Other Comprehensive Loss of the Operating Partnership (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance		$ (6,980,000)
Ending Balance	(11,810,000)	(6,980,000)
Deferred net losses from terminated hedges	11,300,000	11,800,000
SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	(7,256,000)
Other comprehensive (loss) income before reclassifications	(8,108,000)
Amounts reclassified from accumulated other comprehensive income	3,078,000
Ending Balance	(12,286,000)
Deferred net losses from terminated hedges	11,700,000	12,200,000
Net unrealized loss on derivative instruments | SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	(9,845,000)
Other comprehensive (loss) income before reclassifications	(7,521,000)
Amounts reclassified from accumulated other comprehensive income	2,747,000
Ending Balance	(14,619,000)
Unrealized gain and (loss) on marketable securities | SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	2,689,000
Other comprehensive (loss) income before reclassifications	650,000
Amounts reclassified from accumulated other comprehensive income	0
Ending Balance	3,339,000
Joint venture | Net unrealized loss on derivative instruments | SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	(100,000)
Other comprehensive (loss) income before reclassifications	(1,237,000)
Amounts reclassified from accumulated other comprehensive income	331,000
Ending Balance	$ (1,006,000)