Stockholders' Equity of the Company - Additional Information (Details)				1 Months Ended			12 Months Ended
		Jan. 21, 2021	Jan. 20, 2021	Dec. 31, 2020 $ / shares shares	Dec. 31, 2019 $ / shares shares	Dec. 31, 2018 $ / shares shares	Dec. 31, 2020 $ / shares shares	Dec. 31, 2019 $ / shares shares	Dec. 31, 2018 $ / shares shares	Dec. 31, 2017 shares
Class of Stock [Line Items]
Authorized capital stock (in shares)				260,000,000			260,000,000
Authorized shares, par value (in dollars per share) | $ / shares				$ 0.01			$ 0.01
Common stock, shares authorized (in shares)				160,000,000	160,000,000		160,000,000	160,000,000
Common stock, par value (in dollars per share) | $ / shares				$ 0.01	$ 0.01		$ 0.01	$ 0.01
Excess stock, shares authorized (shares)				75,000,000			75,000,000
Excess stock, par value (in dollars per share) | $ / shares				$ 0.01			$ 0.01
Preferred stock, shares authorized (shares)				25,000,000			25,000,000
Preferred stock, par (in dollars per share) | $ / shares				$ 0.01			$ 0.01
Excess shares issued (shares)				0			0
Cash distribution declared, per common share (in dollars per share) | $ / shares				$ 0.3122	$ 0.9108	$ 0.8748	$ 4.7908	3.5352	$ 3.3834
SL Green Operating Partnership
Class of Stock [Line Items]
Cash distribution declared, per common share (in dollars per share) | $ / shares							$ 4.7908	$ 3.5352	$ 3.3834
Common Stock
Class of Stock [Line Items]
Shares, outstanding (in shares)	[1]			68,508,000	76,956,000	81,311,000	68,508,000	76,956,000	81,311,000	90,172,000
Common Stock | Subsequent Event
Class of Stock [Line Items]
Reverse stock split conversion ratio		1.02918	1.02918
Common Stock | SL Green Operating Partnership
Class of Stock [Line Items]
Shares, outstanding (in shares)				68,508,127			68,508,127

[1] On January 21, 2021, we completed a reverse stock split whereby every 1.02918 SL Green common share was combined into 1 SL Green common share. We have retroactively adjusted the outstanding share counts, share activity, cash distributions declared, and earnings per share, as if the reverse split occurred on December 31, 2017.