Noncontrolling Interests on the Company's Consolidated Financial Statements (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017 USD ($) shares $ / shares	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) shares $ / shares	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) shares	Mar. 31, 2016 shares	Aug. 31, 2015 shares	Jul. 31, 2015 shares	Jun. 30, 2015 shares	Feb. 28, 2015 shares	Aug. 31, 2014 shares	Jan. 31, 2012 $ / shares
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $			$ 473,882,000
Net income | $	$ 419,000	$ 5,586,000	895,000	$ 6,508,000
Accumulated other comprehensive income allocation | $	(100,000)	(53,000)	(299,000)	(375,000)
Balance at end of period | $	$ 487,660,000		$ 487,660,000		$ 473,882,000
Number of company common stock issued on conversion of Series B preferred units			6.71348
SL Green Operating Partnership
Organization
Noncontrolling interest in the operating partnership (as a percent)	4.43%		4.43%		4.16%
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares) | shares	4,561,513		4,561,513		4,363,716
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	4,561,513.000		4,561,513.000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $			$ 473,882,000	424,206,000	$ 424,206,000
Distributions | $			(7,112,000)		(12,671,000)
Issuance of common units | $			20,824,000		78,495,000
Redemption of common units | $			(13,242,000)		(31,805,000)
Net income | $			895,000		10,136,000
Accumulated other comprehensive income allocation | $	$ (100,000)	$ (53,000)	(299,000)	$ (375,000)	1,299,000
Fair value adjustment | $			12,712,000		4,222,000
Balance at end of period | $	$ 487,660,000		$ 487,660,000		$ 473,882,000
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) | shares	1,902,000		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		$ 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) | shares	60		60
Mandatory liquidation preference (in dollars per share) | $	$ 1,000.00		$ 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) | shares											563,954
Dividend rate preferred units (as a percent)			3.50%
Liquidation preference of preferred units (in dollars per share)	$ 25.00		$ 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		$ 134.67
Preferred units, shares authorized (in shares) | shares	700,000		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) | shares											378,634
Dividend rate preferred units (as a percent)			4.00%
Liquidation preference of preferred units (in dollars per share)	$ 25.00		$ 25.00
Annual dividends on preferred units (in dollars per share)			$ 1.00
Preferred units, shares authorized (in shares) | shares	500,000		500,000
SL Green Operating Partnership | Series M Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares										1,600,000
Dividend rate preferred units (as a percent)			3.75%
Liquidation preference of preferred units (in dollars per share)	$ 25.00		$ 25.00
Annual dividends on preferred units (in dollars per share)			$ 0.9375
Preferred units, shares authorized (in shares) | shares	1,600,000		1,600,000
SL Green Operating Partnership | Series N Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares									552,303
Dividend rate preferred units (as a percent)			3.00%
Liquidation preference of preferred units (in dollars per share)	$ 25.00		$ 25.00
Annual dividends on preferred units (in dollars per share)			$ 0.75
Preferred units, shares authorized (in shares) | shares	552,303		552,303
SL Green Operating Partnership | Series O Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)			6.25%
Preferred units, shares authorized (in shares) | shares	1		1
SL Green Operating Partnership | Series P Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	200,000		200,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares								200,000
Dividend rate preferred units (as a percent)			4.00%
Liquidation preference of preferred units (in dollars per share)	$ 25.00		$ 25.00
Annual dividends on preferred units (in dollars per share)			$ 1.00
SL Green Operating Partnership | Series Q Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	268,000		268,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares								268,000
Dividend rate preferred units (as a percent)			3.50%
Liquidation preference of preferred units (in dollars per share)	$ 25.00		$ 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)	$ 148.95		$ 148.95
SL Green Operating Partnership | Series R Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	400,000		400,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares							400,000
Dividend rate preferred units (as a percent)			3.50%
Liquidation preference of preferred units (in dollars per share)	$ 25.00		$ 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)	$ 154.89		$ 154.89
SL Green Operating Partnership | Series S Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	1,077,280		1,077,280
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares							1,077,280
Dividend rate preferred units (as a percent)			4.00%
Liquidation preference of preferred units (in dollars per share)	$ 25.00		$ 25.00
Annual dividends on preferred units (in dollars per share)			$ 1.00
SL Green Operating Partnership | Series T Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	230,000		230,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares						230,000
Dividend rate preferred units (as a percent)			2.75%
Liquidation preference of preferred units (in dollars per share)	$ 25.00		$ 25.00
Annual dividends on preferred units (in dollars per share)			0.6875
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 119.02		$ 119.02
SL Green Operating Partnership | Series U Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	680,000		680,000
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares						680,000
Dividend rate preferred units (as a percent)			4.50%
Liquidation preference of preferred units (in dollars per share)	$ 25.00		$ 25.00
Annual dividends on preferred units (in dollars per share)			1.125
SL Green Operating Partnership | Series U Preferred Units | Minimum
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Annual dividends on preferred units (in dollars per share)			$ 0.75
SL Green Operating Partnership | Series A Preferred Units
Organization
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	109,161		109,161
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares							109,161
Dividend rate preferred units (as a percent)			3.50%
Liquidation preference of preferred units (in dollars per share)	$ 1,000.00		$ 1,000.00
Annual dividends on preferred units (in dollars per share)			$ 35.00
SL Green Operating Partnership | Series B Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of preferred units issued (in shares) | shares	0		0