Investments in Unconsolidated Joint Ventures (Schedules of Combined Financial Statements for the Unconsolidated Joint Ventures)(Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Assets
Commercial real estate property, net	$ 12,788,076		$ 12,788,076		$ 14,620,896
Other assets	979,474		979,474		850,939
Liabilities and members' equity
Mortgages and other loans payable, net	5,524,110		5,524,110		6,881,920
Other liabilities	243,011		243,011		168,477
Company's investments in unconsolidated joint ventures	1,126,486		1,126,486		1,203,858
Combined statements of income for the unconsolidated joint ventures
Operating expenses	75,324	$ 70,114	154,844	$ 146,891
Ground rent	8,307	8,086	16,615	16,274
Real estate taxes	62,124	56,286	123,798	112,009
Interest expense, net of interest income	89,089	75,746	183,761	151,553
Amortization of deferred financing costs	7,433	5,952	15,365	12,567
Transaction related costs	2,115	3,067	3,394	4,210
Depreciation and amortization	425,042	199,565	604,350	307,902
Total expenses	693,918	442,016	1,150,643	800,070
Company's equity in net income from unconsolidated joint ventures	5,841	2,994	15,937	7,024
SL Green Operating Partnership
Assets
Commercial real estate property, net	12,788,076		12,788,076		14,620,896
Other assets	979,474		979,474		850,939
Liabilities and members' equity
Mortgages and other loans payable, net	5,524,110		5,524,110		6,881,920
Other liabilities	243,011		243,011		168,477
Company's investments in unconsolidated joint ventures	1,126,486		1,126,486		1,203,858
Combined statements of income for the unconsolidated joint ventures
Operating expenses	75,324	70,114	154,844	146,891
Ground rent	8,307	8,086	16,615	16,274
Real estate taxes	62,124	56,286	123,798	112,009
Interest expense, net of interest income	89,089	75,746	183,761	151,553
Amortization of deferred financing costs	7,433	5,952	15,365	12,567
Transaction related costs	2,115	3,067	3,394	4,210
Depreciation and amortization	425,042	199,565	604,350	307,902
Total expenses	693,918	442,016	1,150,643	800,070
Company's equity in net income from unconsolidated joint ventures	5,841	2,994	15,937	7,024
Joint venture
Investment in Unconsolidated Joint Ventures
Management fees, base revenue	2,000	2,500	2,100	4,900
Assets
Commercial real estate property, net	6,510,775		6,510,775		6,122,468
Debt and preferred equity investments, net	304,901		304,901		145,878
Other assets	741,839		741,839		715,840
Total assets	7,557,515		7,557,515		6,984,186
Liabilities and members' equity
Mortgages and other loans payable, net	4,922,493		4,922,493		4,266,548
Other liabilities	534,611		534,611		523,160
Members' equity	2,100,411		2,100,411		2,194,478
Total liabilities and members' equity	7,557,515		7,557,515		$ 6,984,186
Combined statements of income for the unconsolidated joint ventures
Total revenues	151,575	143,535	314,087	272,451
Operating expenses	27,166	26,345	54,420	51,831
Ground rent	3,715	2,572	6,926	5,164
Real estate taxes	24,332	22,335	48,542	41,711
Interest expense, net of interest income	46,351	51,715	96,087	95,722
Amortization of deferred financing costs	7,276	3,145	10,512	6,155
Transaction related costs	0	3	0	11
Depreciation and amortization	37,294	37,894	75,145	70,878
Total expenses	146,134	144,009	291,632	271,472
Loss on early extinguishment of debt	0	0	(1,606)	(833)
Net income (loss) before gain on sale	5,441	(474)	20,849	146
Company's equity in net income from unconsolidated joint ventures	$ 5,841	$ 2,994	$ 15,937	$ 7,024