Noncontrolling Interests on the Company's Consolidated Financial Statements - Additional Information (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) shares $ / shares	Dec. 31, 2018 USD ($) unit	Dec. 31, 2017 USD ($)
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $	$ 387,805
Distributions | $	(478)	$ (8,364)	$ (52,446)
Redemption of common units | $	(25,845)
Net income | $	13,301	12,216	3,995
Accumulated other comprehensive income allocation | $	(2,276)	(66)	(94)
Balance at end of period | $	$ 409,862	387,805
Number of company common stock issued on conversion of Series B preferred units	6.71348
Series B Preferred Stock
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred units, issued (in shares) | shares	0
SL Green Operating Partnership
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $	$ 387,805	461,954
Distributions | $	(14,729)	(15,000)
Issuance of common units | $	19,403	23,655
Redemption of common units | $	(27,962)	(60,718)
Net income | $	13,301	12,216
Accumulated other comprehensive income allocation | $	(2,276)	(66)
Fair value adjustment | $	34,320	(34,236)
Balance at end of period | $	$ 409,862	$ 387,805	461,954
SL Green Operating Partnership
Organization
Noncontrolling interest in the operating partnership (as a percent)	5.03%	4.70%
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares)	4,195,875	4,130,579
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	4,195,875
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Distributions | $	$ (478)	$ (8,364)	(52,446)
Redemption of common units | $	(25,845)
Accumulated other comprehensive income allocation | $	$ (2,276)	$ (66)	$ (94)
SL Green Operating Partnership | Series G Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	1,902,000
Number of preferred units issued (in shares) | shares	1,902,000
Annual dividends on preferred units (in dollars per share)	$ 1.1250
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (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
Preferred Units, shares authorized (in shares) | shares	60
Number of preferred units issued (in shares) | shares	60
Annual dividends on preferred units (in dollars per share)	$ 70.0000
Liquidation preference of preferred units (in dollars per share)	1,000.00
Conversion Price Per Unit (in dollars per share)	$ 29.12
SL Green Operating Partnership | Series K Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	700,000
Number of preferred units issued (in shares) | shares	563,954
Annual dividends on preferred units (in dollars per share)	$ 0.8750
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	$ 134.67
SL Green Operating Partnership | Series L Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	500,000
Number of preferred units issued (in shares) | shares	378,634
Annual dividends on preferred units (in dollars per share)	$ 1.0000
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series M Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	1,600,000
Number of preferred units issued (in shares) | shares	1,600,000
Annual dividends on preferred units (in dollars per share)	$ 0.9375
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series N Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	552,303
Number of preferred units issued (in shares) | shares	552,303
Annual dividends on preferred units (in dollars per share)	$ 0.7500
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series O Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	1
Number of preferred units issued (in shares) | shares	1
Annual dividends on preferred units (in dollars per share)	$ (6)
Liquidation preference of preferred units (in dollars per share)	(6)
Conversion Price Per Unit (in dollars per share)	$ 0
Preferred stock, dividend, multiplier per common unit distribution	1,350
SL Green Operating Partnership | Series P Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	200,000
Number of preferred units issued (in shares) | shares	200,000
Annual dividends on preferred units (in dollars per share)	$ 1.0000
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series Q Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	268,000
Number of preferred units issued (in shares) | shares	268,000
Annual dividends on preferred units (in dollars per share)	$ 0.8750
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	$ 148.95
SL Green Operating Partnership | Series R Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	400,000
Number of preferred units issued (in shares) | shares	400,000
Annual dividends on preferred units (in dollars per share)	$ 0.8750
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	$ 154.89
SL Green Operating Partnership | Series S Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	1,077,280
Number of preferred units issued (in shares) | shares	1,077,280
Annual dividends on preferred units (in dollars per share)	$ 1.0000
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series T Preferred Stock
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	230,000
Number of preferred units issued (in shares) | shares	230,000
Annual dividends on preferred units (in dollars per share)	$ 0.6875
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	$ 119.02
SL Green Operating Partnership | Series U Preferred Stock
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	680,000
Number of preferred units issued (in shares) | shares	680,000
Annual dividends on preferred units (in dollars per share)	$ 1.1250
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series A Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	109,161
Number of preferred units issued (in shares) | shares	109,161
Annual dividends on preferred units (in dollars per share)	$ 35.0000
Liquidation preference of preferred units (in dollars per share)	1,000.00
Conversion Price Per Unit (in dollars per share)	$ 0
SL Green Operating Partnership | Series V Preferred Stock
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Preferred Units, shares authorized (in shares) | shares	40,000
Number of preferred units issued (in shares) | shares	40,000
Annual dividends on preferred units (in dollars per share)	$ 0.8750
Liquidation preference of preferred units (in dollars per share)	25.00
Conversion Price Per Unit (in dollars per share)	0
Minimum | SL Green Operating Partnership | Series A Preferred Units
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	$ 0.75