Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Rental revenue, net	$ 1,100,993	$ 1,323,767	$ 1,245,981
Escalation and reimbursement	172,939	196,858	178,512
Investment income	193,871	213,008	181,128
Other income	43,670	130,348	57,208
Total revenues	1,511,473	1,863,981	1,662,829
Expenses
Operating expenses, including $21,400 in 2017, $21,890 in 2016, $20,071 in 2015 of related party expenses	293,364	312,859	301,624
Real estate taxes	244,323	248,388	232,702
Ground rent	33,231	33,261	32,834
Interest expense, net of interest income	257,045	321,199	323,870
Amortization of deferred financing costs	16,498	24,564	27,348
Depreciation and amortization	403,320	821,041	560,887
Transaction related costs	(1,834)	7,528	11,430
Marketing, general and administrative	100,498	99,759	94,873
Total expenses	1,346,445	1,868,599	1,585,568
Income (loss) from continuing operations before equity in net income from unconsolidated joint ventures, equity in net 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, gain (loss) on sale of marketable securities and loss on early extinguishment of debt	165,028	(4,618)	77,261
Equity in net income from unconsolidated joint ventures	21,892	11,874	13,028
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	16,166	44,009	15,844
Purchase price fair value adjustment	0	0	40,078
Gain on sale of real estate, net	73,241	238,116	175,974
Depreciable real estate reserves	(178,520)	(10,387)	(19,226)
Gain (loss) on sale of investment in marketable securities	3,262	(83)	0
Loss on early extinguishment of debt	0	0	(49)
Income from continuing operations	101,069	278,911	302,910
Net income from discontinued operations	0	0	427
Gain on sale of discontinued operations	0	0	14,122
Net income	101,069	278,911	317,459
Net (income) loss attributable to noncontrolling interests:
Noncontrolling interests in the Operating Partnership	(3,995)	(10,136)	(10,565)
Net (income) loss attributable to noncontrolling interests in other partnerships	15,701	(7,644)	(15,843)
Preferred unit distributions	(11,401)	(11,235)	(6,967)
Net income (loss) attributable to SL Green/SLGOP	101,374	249,896	284,084
Preferred stock/unit redemption costs	0	0	0
Perpetual preferred stock dividends	(14,950)	(14,950)	(14,952)
Amounts attributable to SL Green common stockholders:
Income (loss) from continuing operations before purchase price fair value adjustment, gains on sale and discontinued operations	171,600	(25,552)	50,502
Purchase price fair value adjustment	0	0	38,563
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	15,452	42,189	15,245
Net income from discontinued operations	0	0	411
Gain on sale of discontinued operations	0	0	13,588
Gain on sale of real estate, net	70,005	228,266	169,322
Depreciable real estate reserves	(170,633)	(9,957)	(18,499)
Net income attributable to SL Green common stockholders	$ 86,424	$ 234,946	$ 269,132
Basic earnings per share:
Income from continuing operations before purchase price fair value adjustment, gains on sale and discontinued operations (usd per share)	$ 1.74	$ (0.26)	$ 0.51
Purchase price fair value adjustment (usd per share)	0.00	0.00	0.39
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (usd per share)	0.16	0.42	0.15
Net income from discontinued operations (usd per share)	0.00	0.00	0.00
Gain on sale of discontinued operations (usd per share)	0.00	0.00	0.14
Gain on sale of real estate (in dollars per share)	0.71	2.29	1.71
Depreciable real estate reserves (in dollars per share)	(1.73)	(0.10)	(0.19)
Net income attributable to SL Green common stockholders (usd per share)	0.88	2.35	2.71
Diluted earnings per share:
Income from continuing operations before purchase price fair value adjustment, gains on sale and discontinued operations (usd per share)	1.74	(0.25)	0.51
Purchase price fair value adjustment (usd per share)	0.00	0.00	0.39
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (usd per share)	0.16	0.42	0.15
Net income from discontinued operations (usd per share)	0.00	0.00	0.00
Gain on sale of discontinued operations (usd per share)	0.00	0.00	0.14
Gain on sale of real estate (in dollars per share)	0.71	2.27	1.70
Depreciable real estate reserves (in dollars per share)	(1.74)	(0.10)	(0.19)
Net income attributable to SL Green common stockholders (usd per share)	$ 0.87	$ 2.34	$ 2.70
Basic weighted average common shares outstanding (in shares)	98,571	100,185	99,345
Diluted weighted average common shares and common share equivalents outstanding (in shares)	103,403	104,881	103,734
SL Green Operating Partnership
Revenues
Rental revenue, net	$ 1,100,993	$ 1,323,767	$ 1,245,981
Escalation and reimbursement	172,939	196,858	178,512
Investment income	193,871	213,008	181,128
Other income	43,670	130,348	57,208
Total revenues	1,511,473	1,863,981	1,662,829
Expenses
Operating expenses, including $21,400 in 2017, $21,890 in 2016, $20,071 in 2015 of related party expenses	293,364	312,859	301,624
Real estate taxes	244,323	248,388	232,702
Ground rent	33,231	33,261	32,834
Interest expense, net of interest income	257,045	321,199	323,870
Amortization of deferred financing costs	16,498	24,564	27,348
Depreciation and amortization	403,320	821,041	560,887
Transaction related costs	(1,834)	7,528	11,430
Marketing, general and administrative	100,498	99,759	94,873
Total expenses	1,346,445	1,868,599	1,585,568
Income (loss) from continuing operations before equity in net income from unconsolidated joint ventures, equity in net 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, gain (loss) on sale of marketable securities and loss on early extinguishment of debt	165,028	(4,618)	77,261
Equity in net income from unconsolidated joint ventures	21,892	11,874	13,028
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	16,166	44,009	15,844
Purchase price fair value adjustment	0	0	40,078
Gain on sale of real estate, net	73,241	238,116	175,974
Depreciable real estate reserves	(178,520)	(10,387)	(19,226)
Gain (loss) on sale of investment in marketable securities	3,262	(83)	0
Loss on early extinguishment of debt	0	0	(49)
Income from continuing operations	101,069	278,911	302,910
Net income from discontinued operations	0	0	427
Gain on sale of discontinued operations	0	0	14,122
Net income	101,069	278,911	317,459
Net (income) loss attributable to noncontrolling interests:
Net (income) loss attributable to noncontrolling interests in other partnerships	15,701	(7,644)	(15,843)
Preferred unit distributions	(11,401)	(11,235)	(6,967)
Net income (loss) attributable to SL Green/SLGOP	105,369	260,032	294,649
Preferred stock/unit redemption costs	0	0	0
Perpetual preferred stock dividends	(14,950)	(14,950)	(14,952)
Net income attributable to SLGOP common unitholders	90,419	245,082	279,697
Amounts attributable to SL Green common stockholders:
Income (loss) from continuing operations before purchase price fair value adjustment, gains on sale and discontinued operations	179,532	(26,656)	52,478
Purchase price fair value adjustment	0	0	40,078
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	16,166	44,009	15,844
Net income from discontinued operations	0	0	427
Gain on sale of discontinued operations	0	0	14,122
Gain on sale of real estate, net	73,241	238,116	175,974
Depreciable real estate reserves	$ (178,520)	$ (10,387)	$ (19,226)
Basic earnings per share:
Income from continuing operations before gains on sale and discontinued operations (usd per share)	$ 1.74	$ (0.26)	$ 0.51
Purchase price fair value adjustment (usd per share)	0.00	0.00	0.39
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (usd per share)	0.16	0.42	0.15
Net income from discontinued operations (usd per share)	0.00	0.00	0.00
Gain on sale of discontinued operations (usd per share)	0.00	0.00	0.14
Gain on sale of real estate (in dollars per share)	0.71	2.29	1.71
Depreciable real estate reserves (in dollars per share)	(1.73)	(0.10)	(0.19)
Net income attributable to SLGOP common unitholders (usd per share)	0.88	2.35	2.71
Diluted earnings per share:
Income from continuing operations before gains on sale and discontinued operations (usd per share)	1.74	(0.25)	0.51
Purchase price fair value adjustment (usd per share)	0.00	0.00	0.39
Equity in net gain on sale of interest in unconsolidated joint venture/real estate (usd per share)	0.16	0.42	0.15
Net income from discontinued operations (usd per share)	0.00	0.00	0.00
Gain on sale of discontinued operations (usd per share)	0.00	0.00	0.14
Gain on sale of real estate (in dollars per share)	0.71	2.27	1.70
Depreciable real estate reserves (in dollars per share)	(1.74)	(0.10)	(0.19)
Net income attributable to SLGOP common unitholders (usd per share)	$ 0.87	$ 2.34	$ 2.70
Basic weighted average common shares outstanding (in shares)	103,127	104,508	103,244
Basic weighted average common units outstanding (in shares)	103,127	104,508	103,244
Diluted weighted average common shares and common share equivalents outstanding (in shares)	103,403	104,881	103,734
Diluted weighted average common units and common unit equivalents outstanding (in shares)	103,403	104,881	103,734