Stockholders' Equity of the Company (Earnings per Share)(Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Basic Earnings:
Income attributable to SL Green common stockholders	$ 133,457	$ (39,106)	$ 156,678	$ 4,171
Diluted Earnings:
Income attributable to SL Green common stockholders	$ 139,043	$ (39,106)	$ 163,186	$ 4,337
Basic Shares:
Weighted average common shares outstanding (shares)	100,134,000	99,579,000	100,093,000	98,994,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (shares)	4,342,000	0	4,158,000	3,936,000
Stock-based compensation plans (shares)	316,000	0	282,000	493,000
Diluted weighted average common stock outstanding (shares)	104,792,000	99,579,000	104,533,000	103,423,000
Common stock shares excluded from the diluted shares outstanding (shares)	739,636	845,026	228,122	748,000
Common stock shares excluded from the diluted shares outstanding due to net loss (shares)		4,367,272
Common Stock
Effect of Dilutive Securities:
Redemption of units to common shares	$ 5,586	$ 0	$ 6,508	$ 166