Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Total revenues	$ 386,627	$ 390,274	$ 380,631	$ 362,446	$ 350,451	$ 338,782	$ 340,888	$ 340,944	$ 1,519,978	$ 1,371,065	$ 1,290,052
Income from continuing before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, (loss) gain on early extinguishment of debt, loss on sale of investment in marketable securities, net of noncontrolling interests	40,379	46,863	47,035	39,416	27,478	19,895	27,398	37,300	174,963	118,062	59,400
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	673	16,496	1,444	104,640	7,538	(354)	(3,583)	0	123,253	3,601	37,053
Purchase price fair value adjustment	0	(4,000)	71,446	0	0	0	(2,305)	0	65,059	(2,239)	0
(Loss) gain on early extinguishment of debt	(6,865)	(24,475)	(1,028)	3	5	0	(10)	(18,513)	(32,365)	(18,518)	(6,978)
Gain (loss) on sale of investment in marketable securities	3,895	0	0	0	0	0	(8)	(57)	3,895	(65)	4,940
Net income (loss) from discontinued operations	3,626	4,035	5,645	5,769	5,836	7,435	5,943	6,473	19,075	25,687	32,240
Gain on sale of discontinued operations	18,817	29,507	114,735	0	0	13,787	0	1,113	163,059	14,900	6,627
Net income attributable to SL Green	60,525	68,426	239,277	149,828	40,857	40,763	27,435	26,316	518,056	135,371	196,405
Preferred stock redemption costs	0	0	0	0	0	0	(12,160)	0	0	(12,160)	(10,010)
Perpetual preferred stock dividends	(3,738)	(3,738)	(3,738)	(3,738)	(3,737)	(3,738)	(6,999)	(7,407)	(14,952)	(21,881)	(30,411)
Net income attributable to SL Green common stockholders	56,787	64,688	235,539	146,090	37,120	37,025	8,276	18,909	503,104	101,330	155,984
Net income per common share-Basic (usd per share)	$ 0.59	$ 0.68	$ 2.47	$ 1.54	$ 0.39	$ 0.40	$ 0.09	$ 0.21	$ 5.25	$ 1.10	$ 1.75
Net income per common share-Diluted (usd per share)	$ 0.59	$ 0.68	$ 2.46	$ 1.53	$ 0.39	$ 0.40	$ 0.09	$ 0.21	$ 5.23	$ 1.10	$ 1.74
SL Green Operating Partnership
Condensed Financial Statements, Captions [Line Items]
Total revenues	386,627	390,274	380,631	362,446	350,451	338,782	340,888	340,944	1,519,978	1,371,065	1,290,052
Income from continuing before equity in net gain on sale of interest in unconsolidated joint venture/real estate, purchase price fair value adjustment, (loss) gain on early extinguishment of debt, loss on sale of investment in marketable securities, net of noncontrolling interests	42,837	49,499	55,680	44,144	28,592	21,005	27,642	37,855	174,963	118,062	59,400
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	673	16,496	1,444	104,640	7,538	(354)	(3,583)	0	123,253	3,601	37,053
Purchase price fair value adjustment	0	(4,000)	71,446	0	0	0	(2,305)	0
(Loss) gain on early extinguishment of debt	(6,865)	(24,475)	(1,028)	3	5	0	(10)	(18,513)	(32,365)	(18,518)	(6,978)
Gain (loss) on sale of investment in marketable securities	3,895	0	0	0	0	0	(8)	(57)	3,895	(65)	4,940
Net income (loss) from discontinued operations	3,626	4,035	5,645	5,769	5,836	7,435	5,943	6,473	19,075	25,687	32,240
Gain on sale of discontinued operations	18,817	29,507	114,735	0	0	13,787	0	1,113	163,059	14,900	6,627
Net income attributable to SL Green	62,983	71,062	247,922	154,556	41,971	41,873	27,679	26,871	536,523	138,394	202,002
Preferred stock redemption costs	0	0	0	0	0	0	(12,160)	0
Perpetual preferred stock dividends	(3,738)	(3,738)	(3,738)	(3,738)	(3,737)	(3,738)	(6,999)	(7,407)
Net income attributable to SLGOP common unitholders	$ 59,245	$ 67,324	$ 244,184	$ 150,818	$ 38,234	$ 38,135	$ 8,520	$ 19,464	$ 521,571	$ 104,353	$ 161,581
Net income per common share-Basic (usd per share)	$ 0.59	$ 0.68	$ 2.47	$ 1.54	$ 0.39	$ 0.40	$ 0.09	$ 0.21
Net income per common share-Diluted (usd per share)	$ 0.59	$ 0.68	$ 2.46	$ 1.53	$ 0.39	$ 0.40	$ 0.09	$ 0.21