Quarterly Financial Data of the Company (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Income Statements, Captions [Line Items]
Total revenues									$ 1,863,981	$ 1,662,829	$ 1,519,978
Income (loss) from continuing operations before equity in net income from unconsolidated joint ventures, equity in net (loss) gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves and gain (loss) on early extinguishment of debt									(4,618)	77,261	174,963
Equity in net income from unconsolidated joint ventures	$ (95)	$ (3,968)	$ 5,841	$ 10,096	$ 2,377	$ 3,627	$ 2,994	$ 4,030	11,874	13,028	26,537
Equity in net gain on sale of interest in unconsolidated joint venture/real estate									44,009	15,844	123,253
Purchase price fair value adjustment									0	38,563	65,059
Gain on sale of real estate, net									238,116	175,974	0
Depreciable real estate reserves									(10,387)	(19,226)	0
Change in unrealized gain (loss) on marketable securities									3,677	(607)	(2,237)
Loss on early extinguishment of debt									0	(49)	(32,365)
Net income from discontinued operations									0	427	19,075
Gain on sale of discontinued operations									0	14,122	163,059
Net income (loss) attributable to SL Green/SLGOP									249,896	284,084	518,056
Perpetual preferred stock dividends									(14,950)	(14,952)	(14,952)
Net income attributable to SL Green common stockholders									$ 234,946	$ 269,132	$ 503,104
Net income (loss) attributable to common stockholders per common share - basic (usd per share)									$ 2.35	$ 2.71	$ 5.25
Net income (loss) attributable to common stockholders per common share - diluted (usd per share)									$ 2.34	$ 2.70	$ 5.23
SL Green Realty Corp
Condensed Income Statements, Captions [Line Items]
Total revenues	374,242	416,681	617,614	455,444	425,390	432,066	409,074	396,299
Income (loss) from continuing operations before equity in net income from unconsolidated joint ventures, equity in net (loss) gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, gain on sale of real estate, depreciable real estate reserves and gain (loss) on early extinguishment of debt	26,278	46,689	(76,304)	(1,281)	54,591	17,367	(32,942)	38,245
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	421	225	33,448	9,915	(206)	15,281	769	0
Purchase price fair value adjustment					40,078	0	0	0
Gain on sale of real estate, net	27,366	397	196,580	13,773	16,270	159,704	0	0
Depreciable real estate reserves	0	0	(10,387)	0	0	(19,226)	0	0
Change in unrealized gain (loss) on marketable securities	0	0	(83)	0
Distributions Preferred Units	(6,217)	(5,353)	(11,901)	(5,544)	(9,208)	(9,357)	(6,189)	(8,621)
Loss on early extinguishment of debt					0	0	0	(49)
Net income from discontinued operations					0	0	0	427
Gain on sale of discontinued operations					1,139	0	0	12,983
Net income (loss) attributable to SL Green/SLGOP	47,753	37,990	137,194	26,959	105,041	167,396	(35,368)	47,015
Perpetual preferred stock dividends	(3,737)	(3,738)	(3,737)	(3,738)	(3,738)	(3,738)	(3,738)	(3,738)
Net income attributable to SL Green common stockholders	$ 44,016	$ 34,252	$ 133,457	$ 23,221	$ 101,303	$ 163,658	$ (39,106)	$ 43,277
Net income (loss) attributable to common stockholders per common share - basic (usd per share)	$ 0.44	$ 0.34	$ 1.33	$ 0.23	$ 1.02	$ 1.64	$ (0.39)	$ 0.44
Net income (loss) attributable to common stockholders per common share - diluted (usd per share)	$ 0.44	$ 0.34	$ 1.33	$ 0.23	$ 1.01	$ 1.64	$ (0.39)	$ 0.44