Stockholders' Equity of the Company - Additional Information (Details)			3 Months Ended	12 Months Ended
	Jan. 15, 2021 $ / shares	Jan. 08, 2021	Mar. 31, 2021 USD ($) increase $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Jan. 07, 2021 $ / shares	Mar. 31, 2020 shares	Jun. 30, 2018 USD ($)	Aug. 31, 2016 USD ($)
Equity, Class of Treasury Stock [Line Items]
Authorized capital stock (shares) | shares			260,000,000
Authorized shares, par value (in dollars per share) | $ / shares			$ 0.01
Common stock, shares authorized (in shares) | shares			160,000,000	160,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.01	$ 0.01
Excess stock, shares authorized (shares) | shares			75,000,000
Excess stock, par value (in dollars per share) | $ / shares			$ 0.01
Preferred stock, shares authorized (shares) | shares			25,000,000
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.01
Excess shares issued (shares) | shares			0
Share repurchased (in shares) | shares			1,306,460	8,529,279	4,465,857	9,468,617	8,105,881
Average price paid per share (in dollars per share) | $ / shares			$ 61.46	$ 62.39	$ 86.06	$ 99.03	$ 104.61
2016 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount | $				$ 500,000,000.0	$ 500,000,000.0	$ 500,000,000.0	$ 500,000,000.0			$ 500,000,000.0	$ 1,000,000,000.0
Number of increases to share repurchase program | increase			5
Share repurchased (in shares) | shares			31,876,094	30,569,634	22,040,355	17,574,498	8,105,881
Stock repurchase program, authorized amount | $			$ 3,500,000,000
Common Stock
Equity, Class of Treasury Stock [Line Items]
Shares, outstanding (in shares) | shares			69,354,000	68,508,000	76,956,000				74,365,000
Share price (in dollars per share) | $ / shares								$ 58.15
Reverse stock split conversion ratio		1.02918
Common Stock | Cash Dividend
Equity, Class of Treasury Stock [Line Items]
Common stock, dividends, per share, cash paid (in dollars per share) | $ / shares	$ 0.3735
Common stock, dividends, per share, stock paid (in dollars per share) | $ / shares	0.0279
Common Stock | Stock Dividend
Equity, Class of Treasury Stock [Line Items]
Common stock, dividends, per share, stock paid (in dollars per share) | $ / shares	$ 0.0343
SL Green Operating Partnership | Common Stock
Equity, Class of Treasury Stock [Line Items]
Shares, outstanding (in shares) | shares			69,353,606