Noncontrolling Interests on the Company's Consolidated Financial Statements - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Redemption and conversion of common units		$ (29,817)		$ (29,817)
Net loss	$ (1,574)	491	$ (27,493)	(1,831)
Accumulated other comprehensive (loss) income allocation	$ 771	3,114	$ 1,425	6,404
SL Green Operating Partnership
Organization
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares)	4,139,334		4,139,334		3,670,343
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Redemption and conversion of common units		(29,817)		(29,817)
Accumulated other comprehensive (loss) income allocation	$ 771	$ 3,114	$ 1,425	6,404
SL Green Operating Partnership | Series A
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Stated Distribution Rate			5.00%
Number of Units Authorized (in shares)	109,161		109,161
Number of Units Issued (in shares)	109,161		109,161
Number of Units Outstanding (in shares)	109,161		109,161
Annual Dividend Per Unit (in dollars per share)			$ 50.0000
Liquidation Preference Per Unit (in dollars per share)	$ 1,000		1,000
Conversion Price Per Unit (in dollars per share)	$ 0		$ 0
Number of company common stock issued on conversion of Series B preferred units	6.71348		6.71348
SL Green Operating Partnership | Series F
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Stated Distribution Rate			7.00%
Number of Units Authorized (in shares)	60		60
Number of Units Issued (in shares)	60		60
Number of Units Outstanding (in shares)	60		60
Annual Dividend Per Unit (in dollars per share)			$ 70.0000
Liquidation Preference Per Unit (in dollars per share)	$ 1,000		1,000
Conversion Price Per Unit (in dollars per share)	$ 29.12		$ 29.12
SL Green Operating Partnership | Series K
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Stated Distribution Rate			3.50%
Number of Units Authorized (in shares)	700,000		700,000
Number of Units Issued (in shares)	563,954		563,954
Number of Units Outstanding (in shares)	341,677		341,677
Annual Dividend Per Unit (in dollars per share)			$ 0.8750
Liquidation Preference Per Unit (in dollars per share)	$ 25.00		25.00
Conversion Price Per Unit (in dollars per share)	$ 134.67		$ 134.67
SL Green Operating Partnership | Series L
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Stated Distribution Rate			4.00%
Number of Units Authorized (in shares)	500,000		500,000
Number of Units Issued (in shares)	378,634		378,634
Number of Units Outstanding (in shares)	372,634		372,634
Annual Dividend Per Unit (in dollars per share)			$ 1.0000
Liquidation Preference Per Unit (in dollars per share)	$ 25.00		25.00
Conversion Price Per Unit (in dollars per share)	$ 0		$ 0
SL Green Operating Partnership | Series R
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Stated Distribution Rate			3.50%
Number of Units Authorized (in shares)	400,000		400,000
Number of Units Issued (in shares)	400,000		400,000
Number of Units Outstanding (in shares)	400,000		400,000
Annual Dividend Per Unit (in dollars per share)			$ 0.8750
Liquidation Preference Per Unit (in dollars per share)	$ 25.00		25.00
Conversion Price Per Unit (in dollars per share)	$ 154.89		$ 154.89
SL Green Operating Partnership | Series S
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Stated Distribution Rate			4.00%
Number of Units Authorized (in shares)	1,077,280		1,077,280
Number of Units Issued (in shares)	1,077,280		1,077,280
Number of Units Outstanding (in shares)	1,077,280		1,077,280
Annual Dividend Per Unit (in dollars per share)			$ 1.0000
Liquidation Preference Per Unit (in dollars per share)	$ 25.00		25.00
Conversion Price Per Unit (in dollars per share)	$ 0		$ 0
SL Green Operating Partnership | Series V
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Stated Distribution Rate			5.00%
Number of Units Authorized (in shares)	40,000		40,000
Number of Units Issued (in shares)	40,000		40,000
Number of Units Outstanding (in shares)	40,000		40,000
Annual Dividend Per Unit (in dollars per share)			$ 1.2500
Liquidation Preference Per Unit (in dollars per share)	$ 25.00		25.00
Conversion Price Per Unit (in dollars per share)	$ 0		$ 0
SL Green Operating Partnership | Series W
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Number of Units Authorized (in shares)	1		1
Number of Units Issued (in shares)	1		1
Number of Units Outstanding (in shares)	1		1
Preferred stock, dividend, multiplier per common unit distribution			1,350
SL Green Operating Partnership | Series B Preferred Stock
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Convertible preferred stock, shares issued upon conversion (in shares)	1		1
Partnership Interest
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at beginning of period			$ 269,993	$ 344,252	$ 344,252
Distributions			(11,225)		(16,272)
Issuance of common units			16,350		22,855
Redemption and conversion of common units			(8,900)		(40,901)
Net loss			(27,493)		(5,794)
Accumulated other comprehensive (loss) income allocation			1,425		5,827
Fair value adjustment			8,072		(39,974)
Balance at end of period	$ 248,222		$ 248,222		$ 269,993
Operating Partnership | SL Green Operating Partnership
Organization
Noncontrolling interest in the operating partnership (as a percent)	6.04%		6.04%		5.39%