Quarterly Financial Data of the Company (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 308,082	$ 313,634	$ 313,024	$ 304,255	$ 317,036	$ 307,545	$ 301,116	$ 301,695	$ 1,238,995	$ 1,227,392	$ 1,511,473
Total expenses	(252,712)	(263,341)	(258,383)	(260,328)	(267,678)	(265,553)	(258,303)	(258,282)	(1,034,764)	(1,049,816)	(1,346,445)
Equity in net income from unconsolidated joint ventures	(11,874)	(9,864)	(7,546)	(5,234)	(2,398)	971	4,702	4,036	(34,518)	7,311	21,892
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	0	0	59,015	17,166	167,445	70,937	72,025	(6,440)	76,181	303,967	16,166
Purchase price and other fair value adjustment	0	3,799	67,631	(2,041)	0	(3,057)	11,149	49,293	69,389	57,385	0
(Loss) gain on sale of real estate, net	(19,241)	3,541	0	(1,049)	(36,984)	(2,504)	(14,790)	23,521	(16,749)	(30,757)	73,241
Depreciable real estate reserves and impairment	0	(7,047)	0	0	(220,852)	(6,691)	0	0	(7,047)	(227,543)	(178,520)
Loss on early extinguishment of debt					(14,889)	(2,194)	0	0	0	(17,083)	0
Noncontrolling interests and preferred unit distributions	(3,086)	(3,827)	(8,901)	(5,239)	838	(7,507)	(8,606)	(8,319)
Net income (loss) attributable to SL Green/SLGOP	21,169	36,895	164,840	47,530	(57,482)	91,947	107,293	105,504	270,434	247,262	101,374
Perpetual preferred stock dividends	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(3,737)	(3,738)	(14,950)	(14,950)	(14,950)
Net income attributable to SL Green common stockholders	$ 17,432	$ 33,157	$ 161,103	$ 43,792	$ (61,219)	$ 88,209	$ 103,556	$ 101,766	$ 255,484	$ 232,312	$ 86,424
Net (loss) income attributable to common stockholders per common share - basic (usd per share)	$ 0.21	$ 0.40	$ 1.94	$ 0.52	$ (0.73)	$ 1.03	$ 1.19	$ 1.12
Net (loss) income attributable to common stockholders per common share - diluted (usd per share)	$ 0.21	$ 0.40	$ 1.94	$ 0.52	$ (0.73)	$ 1.03	$ 1.19	$ 1.12