Consolidated Statements of Operations - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Rental revenue, net	$ 864,978,000	$ 1,100,993,000	$ 1,323,767,000
Escalation and reimbursement	113,596,000	172,939,000	196,858,000
Investment income	201,492,000	193,871,000	213,008,000
Other income	47,326,000	43,670,000	130,348,000
Total revenues	1,227,392,000	1,511,473,000	1,863,981,000
Expenses
Operating expenses, including $17,823 in 2018, $21,400 in 2017, $21,890 in 2016 of related party expenses	229,347,000	293,364,000	312,859,000
Real estate taxes	186,351,000	244,323,000	248,388,000
Ground rent	32,965,000	33,231,000	33,261,000
Interest expense, net of interest income	208,669,000	257,045,000	321,199,000
Amortization of deferred financing costs	12,408,000	16,498,000	24,564,000
Depreciation and amortization	279,507,000	403,320,000	821,041,000
Loan loss and other investment reserves, net of recoveries	6,839,000	0	0
Transaction related costs	1,099,000	(1,834,000)	7,528,000
Marketing, general and administrative	92,631,000	100,498,000	99,759,000
Total expenses	1,049,816,000	1,346,445,000	1,868,599,000
Equity in net income from unconsolidated joint ventures	7,311,000	21,892,000	11,874,000
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	303,967,000	16,166,000	44,009,000
Purchase price and other fair value adjustment	57,385,000	0	0
(Loss) gain on sale of real estate, net	(30,757,000)	73,241,000	238,116,000
Depreciable real estate reserves and impairment	(227,543,000)	(178,520,000)	(10,387,000)
Gain (loss) on sale of investment in marketable securities	0	3,262,000	(83,000)
Loss on early extinguishment of debt	(17,083,000)	0	0
Net income	270,856,000	101,069,000	278,911,000
Net (income) loss attributable to noncontrolling interests:
Noncontrolling interests in the Operating Partnership	(12,216,000)	(3,995,000)	(10,136,000)
Net (income) loss attributable to noncontrolling interests in other partnerships	6,000	15,701,000	(7,644,000)
Preferred unit distributions	(11,384,000)	(11,401,000)	(11,235,000)
Net income (loss) attributable to SL Green/SLGOP	247,262,000	101,374,000	249,896,000
Preferred stock/unit redemption costs	0	0	0
Perpetual preferred stock dividends	(14,950,000)	(14,950,000)	(14,950,000)
Net income attributable to SL Green common stockholders	$ 232,312,000	$ 86,424,000	$ 234,946,000
Basic weighted average common shares outstanding (in shares)	86,753	98,571	100,185
Diluted weighted average common shares and common share equivalents outstanding (in shares)	91,530	103,403	104,881
SL Green Operating Partnership
Revenues
Rental revenue, net	$ 864,978,000	$ 1,100,993,000	$ 1,323,767,000
Escalation and reimbursement	113,596,000	172,939,000	196,858,000
Investment income	201,492,000	193,871,000	213,008,000
Other income	47,326,000	43,670,000	130,348,000
Total revenues	1,227,392,000	1,511,473,000	1,863,981,000
Expenses
Operating expenses, including $17,823 in 2018, $21,400 in 2017, $21,890 in 2016 of related party expenses	229,347,000	293,364,000	312,859,000
Real estate taxes	186,351,000	244,323,000	248,388,000
Ground rent	32,965,000	33,231,000	33,261,000
Interest expense, net of interest income	208,669,000	257,045,000	321,199,000
Amortization of deferred financing costs	12,408,000	16,498,000	24,564,000
Depreciation and amortization	279,507,000	403,320,000	821,041,000
Loan loss and other investment reserves, net of recoveries	6,839,000	0	0
Transaction related costs	1,099,000	(1,834,000)	7,528,000
Marketing, general and administrative	92,631,000	100,498,000	99,759,000
Total expenses	1,049,816,000	1,346,445,000	1,868,599,000
Equity in net income from unconsolidated joint ventures	7,311,000	21,892,000	11,874,000
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	303,967,000	16,166,000	44,009,000
Purchase price and other fair value adjustment	57,385,000	0	0
(Loss) gain on sale of real estate, net	(30,757,000)	73,241,000	238,116,000
Depreciable real estate reserves and impairment	(227,543,000)	(178,520,000)	(10,387,000)
Gain (loss) on sale of investment in marketable securities	0	3,262,000	(83,000)
Loss on early extinguishment of debt	(17,083,000)	0	0
Net income	270,856,000	101,069,000	278,911,000
Net (income) loss attributable to noncontrolling interests:
Net (income) loss attributable to noncontrolling interests in other partnerships	6,000	15,701,000	(7,644,000)
Preferred unit distributions	(11,384,000)	(11,401,000)	(11,235,000)
Net income (loss) attributable to SL Green/SLGOP	259,478,000	105,369,000	260,032,000
Preferred stock/unit redemption costs	0	0	0
Perpetual preferred stock dividends	(14,950,000)	(14,950,000)	(14,950,000)
Net income attributable to SLGOP common unitholders	$ 244,528,000	$ 90,419,000	$ 245,082,000
Basic earnings per unit (in dollars per share)	$ 2.67	$ 0.87	$ 2.34
Diluted earnings per unit (in dollars per share)	$ 2.67	$ 0.87	$ 2.34
Basic weighted average common shares outstanding (in shares)	91,315	103,127	104,508
Basic weighted average common units outstanding (in shares)	91,315	103,127	104,508
Diluted weighted average common shares and common share equivalents outstanding (in shares)	91,530	103,403	104,881
Diluted weighted average common units and common unit equivalents outstanding (in shares)	91,530	103,403	104,881