Noncontrolling Interests on the Company's Consolidated Financial Statements (Details) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2012	Aug. 31, 2014	Oct. 31, 2014
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period	$ 265,476,000
Distributions	(7,019,000)	(14,623,000)	(21,946,000)
Net income	18,467,000	3,023,000	5,597,000
Accumulated other comprehensive income allocation	175,000	611,000	(388,000)
Balance at end of period	469,524,000	265,476,000
SL Green Operating Partnership
Organization
Noncontrolling interest in the operating partnership (as a percent)	3.92%	2.96%
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares)	3,973,016	2,902,317
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)	3,973,016
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period	265,476,000	212,907,000
Distributions	(7,849,000)	(4,146,000)
Issuance of common units	56,469,000	24,750,000
Redemption of common units	(31,653,000)	(17,287,000)
Net income	18,467,000	3,023,000
Accumulated other comprehensive income allocation	175,000	611,000
Fair value adjustment	168,439,000	45,618,000
Balance at end of period	469,524,000	265,476,000
SL Green Operating Partnership | Series G Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)				1,902,000
Dividend rate preferred units (as a percent)				4.50%
Liquidation preference of preferred units (in dollars per share)				$ 25.00
Annual dividends on preferred units (in dollars per share)				$ 1.125
Operating partnership common stock value use for conversion of preferred units (in dollars per share)				$ 88.50
Number of company common stock issue on redemption of operation partnership common units				1
SL Green Operating Partnership | Series F Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)	60
Mandatory liquidation preference	$ 1,000.00
SL Green Operating Partnership | Series K Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)					563,954
Dividend rate preferred units (as a percent)					3.50%
Liquidation preference of preferred units (in dollars per share)					$ 25.00
Annual dividends on preferred units (in dollars per share)					$ 0.875
Operating partnership common stock value use for conversion of preferred units (in dollars per share)					$ 134.67
Preferred Units, Authorized					700,000
SL Green Operating Partnership | Series L Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)					378,634
Dividend rate preferred units (as a percent)					4.00%
Liquidation preference of preferred units (in dollars per share)					$ 25.00
Annual dividends on preferred units (in dollars per share)					$ 1.00
Preferred Units, Authorized					500,000
SL Green Operating Partnership | Series H Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares)						80,000
Dividend rate preferred units (as a percent)						6.00%
Liquidation preference of preferred units (in dollars per share)						$ 25.00
Annual dividends on preferred units (in dollars per share)						$ 0.05833