Noncontrolling Interests on the Company's Consolidated Financial Statements - Additional Information (Details) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) shares $ / shares	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) shares
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Redemption and conversion of common units | $	$ (1,536)
Net income | $	6,202	$ 2,278
Accumulated other comprehensive loss allocation | $	(2,886)	(1,003)
Partnership Interest
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period | $	409,862	387,805	$ 387,805
Distributions | $	(1,284)		(14,729)
Issuance of common units | $	3,680		19,403
Redemption and conversion of common units | $	(18,150)		(27,962)
Net income | $	6,202		13,301
Accumulated other comprehensive loss allocation | $	(2,886)		(2,276)
Fair value adjustment | $	(38,529)		34,320
Balance at end of period | $	$ 358,895		$ 409,862
SL Green Operating Partnership
Organization
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares) | shares	4,144,555		4,195,875
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares	4,144,555
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Redemption and conversion of common units | $	$ (1,536)
Accumulated other comprehensive loss allocation | $	$ (2,886)	$ (1,003)
SL Green Operating Partnership | 3.50% Series A
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	3.50%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 0
Number of company common stock issued on conversion of Series B preferred units	6.71348
SL Green Operating Partnership | 3.50% Series A | Minimum
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	75.00%
SL Green Operating Partnership | 7.00% Series F
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	7.00%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 29.12
SL Green Operating Partnership | 4.50% Series G
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	4.50%
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
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 | 3.50% Series K
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	3.50%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 134.67
SL Green Operating Partnership | 4.00% Series L
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	4.00%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 0
SL Green Operating Partnership | 3.75% Series M
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	3.75%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 0
SL Green Operating Partnership | 4.00% Series P
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	4.00%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 0
SL Green Operating Partnership | 3.50% Series Q
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	3.50%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 148.95
SL Green Operating Partnership | 3.50% Series R
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	3.50%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 154.89
SL Green Operating Partnership | 4.00% Series S
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	4.00%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 0
SL Green Operating Partnership | 2.75% Series T
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	2.75%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 119.02
SL Green Operating Partnership | 4.50% Series U
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	4.50%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 0
SL Green Operating Partnership | 3.50% Series V
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Dividend rate preferred units (as a percent)	3.50%
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 0
SL Green Operating Partnership | Series W
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
Operating partnership common stock value use for conversion of preferred units (in dollars per share)	$ 0
Preferred stock, dividend, multiplier per common unit distribution	1,350
Operating Partnership | SL Green Operating Partnership
Organization
Noncontrolling interest in the operating partnership (as a percent)	5.14%		5.03%