Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2016		Jun. 30, 2015
Operating Activities
Net income (loss)	$ 181,598,000		$ 26,457,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	619,715,000		320,472,000
Equity in net income from unconsolidated joint ventures	(15,937,000)		(7,024,000)
Distributions of cumulative earnings from unconsolidated joint ventures	15,260,000		22,464,000
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(43,363,000)		(769,000)
Depreciable real estate reserves	10,387,000		0
Gain on sale of real estate	(210,353,000.00)		0
Gain on sale of discontinued operations	0		(12,983,000)
Loss on sale of investment in marketable securities	83,000		0
Loss on early extinguishment of debt	0		49,000
Deferred rents receivable	53,042,000		(65,260,000)
Other non-cash adjustments	(164,276,000)	[1]	(3,592,000)
Changes in operating assets and liabilities:
Restricted cash—operations	(10,069,000)		(1,246,000)
Tenant and other receivables	4,820,000		(6,826,000)
Related party receivables	(2,386,000)		340,000
Deferred lease costs	(31,951,000)		(35,918,000)
Other assets	4,362,000		11,410,000
Accounts payable, accrued expenses and other liabilities and security deposits	(33,635,000)		(16,987,000)
Deferred revenue and land leases payable	(3,919,000)		2,872,000
Net cash provided by operating activities	373,378,000		233,459,000
Investing Activities
Acquisitions of real estate property	(37,728,000)		(42,556,000)
Additions to land, buildings and improvements	(157,118,000)		(122,520,000)
Escrowed cash—capital improvements/acquisition deposits/deferred purchase price	76,220,000		(229,853,000)
Investments in unconsolidated joint ventures	(25,389,000)		(109,135,000)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	161,413,000		49,059,000
Net proceeds from disposition of real estate/joint venture interest	1,916,312,000		491,598,000
Proceeds from sale of marketable securities	5,180,000		295,000
Purchases of marketable securities	(331,000)		(7,769,000)
Other investments	(2,987,000)		(9,620,000)
Origination of debt and preferred equity investments	(227,196,000)		(387,216,000)
Repayments or redemption of debt and preferred equity investments	418,371,000		109,784,000
Net cash provided by investing activities	2,126,747,000		(257,933,000)
Financing Activities
Proceeds from mortgages and other loans payable	250,514,000		106,421,000
Repayments of mortgages and other loans payable	(1,663,616,000)		(489,138,000)
Proceeds from revolving credit facility and senior unsecured notes	700,000,000		1,055,000,000
Repayments of revolving credit facility and senior unsecured notes	(1,664,296,000)		(735,007,000)
Proceeds from stock options exercised and DRIP issuance	4,431,000		111,307,000
Proceeds from sale of common stock	0		124,999,000
Redemption of preferred stock	(2,849,000)		(200,000)
Distributions to noncontrolling interests in other partnerships	(9,866,000)		(111,715,000)
Contributions from noncontrolling interests in other partnerships	1,434,000		8,655,000
Distributions to noncontrolling interests in the Operating Partnership	(6,009,000)		(4,693,000)
Dividends/Distributions paid on common and preferred stock/units	(156,234,000)		(127,310,000)
Other obligations related to mortgage loan participations	76,500,000		25,000,000
Deferred loan costs and capitalized lease obligation	(9,307,000)		(4,358,000)
Net cash used in financing activities	(2,479,298,000)		(41,039,000)
Net increase in cash and cash equivalents	20,827,000		(65,513,000)
Cash and cash equivalents at beginning of year	255,399,000		281,409,000
Cash and cash equivalents at end of period	276,226,000		215,896,000
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the operating partnership relating to the investment in unconsolidated joint ventures	51,647,000		0
Redemption of units in the operating partnership	11,795,000		37,992,000
Derivative instruments at fair value	7,701,000		2,000,000
Exchange of debt investment for equity in joint venture	68,581,000		10,151,000
Transfer of restricted cash to operating cash and cash equivalents as a result of sale	0		21,578,000
Acquisition of subsidiary interest from noncontrolling interest	0		20,630,000
Tenant improvements and capital expenditures payable	11,637,000		17,661,000
Fair value adjustment to noncontrolling interest in operating partnership	906,000		20,670,000
Capital lease assets	0		0
Transfer of assets to assets held for sale	1,931,217,000		420,569,000
Transfer of liabilities related to assets held for sale	1,612,008,000		178,252,000
Deferred leasing payable	1,222,000		5,525,000
Removal of fully depreciated commercial real estate properties	13,471,000		0
SL Green Operating Partnership
Operating Activities
Net income (loss)	181,598,000		26,457,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	619,715,000		320,472,000
Equity in net income from unconsolidated joint ventures	(15,937,000)		(7,024,000)
Distributions of cumulative earnings from unconsolidated joint ventures	15,260,000		22,464,000
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(43,363,000)		(769,000)
Depreciable real estate reserves	10,387,000		0
Gain on sale of real estate	(210,353,000)		0
Gain on sale of discontinued operations	0		(12,983,000)
Loss on sale of investment in marketable securities	83,000		0
Loss on early extinguishment of debt	0		49,000
Deferred rents receivable	53,042,000		(65,260,000)
Other non-cash adjustments	(164,276,000)	[1]	(3,592,000)
Changes in operating assets and liabilities:
Restricted cash—operations	(10,069,000)		(1,246,000)
Tenant and other receivables	4,820,000		(6,826,000)
Related party receivables	(2,386,000)		340,000
Deferred lease costs	(31,951,000)		(35,918,000)
Other assets	4,362,000		11,410,000
Accounts payable, accrued expenses and other liabilities and security deposits	(33,635,000)		(16,987,000)
Deferred revenue and land leases payable	(3,919,000)		2,872,000
Net cash provided by operating activities	373,378,000		233,459,000
Investing Activities
Acquisitions of real estate property	(37,728,000)		(42,556,000)
Additions to land, buildings and improvements	(157,118,000)		(122,520,000)
Escrowed cash—capital improvements/acquisition deposits/deferred purchase price	76,220,000		(229,853,000)
Investments in unconsolidated joint ventures	(25,389,000)		(109,135,000)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	161,413,000		49,059,000
Net proceeds from disposition of real estate/joint venture interest	1,916,312,000		491,598,000
Proceeds from sale of marketable securities	5,180,000		295,000
Purchases of marketable securities	(331,000)		(7,769,000)
Other investments	(2,987,000)		(9,620,000)
Origination of debt and preferred equity investments	(227,196,000)		(387,216,000)
Repayments or redemption of debt and preferred equity investments	418,371,000		109,784,000
Net cash provided by investing activities	2,126,747,000		(257,933,000)
Financing Activities
Proceeds from mortgages and other loans payable	250,514,000		106,421,000
Repayments of mortgages and other loans payable	(1,663,616,000)		(489,138,000)
Proceeds from revolving credit facility and senior unsecured notes	700,000,000		1,055,000,000
Repayments of revolving credit facility and senior unsecured notes	(1,664,296,000)		(735,007,000)
Proceeds from stock options exercised and DRIP issuance	4,431,000		111,307,000
Proceeds from sale of common stock	0		124,999,000
Redemption of preferred stock	(2,849,000)		(200,000)
Distributions to noncontrolling interests in other partnerships	(9,866,000)		(111,715,000)
Contributions from noncontrolling interests in other partnerships	1,434,000		8,655,000
Dividends/Distributions paid on common and preferred stock/units	(162,243,000)		(132,003,000)
Other obligations related to mortgage loan participations	76,500,000		25,000,000
Deferred loan costs and capitalized lease obligation	(9,307,000)		(4,358,000)
Net cash used in financing activities	(2,479,298,000)		(41,039,000)
Net increase in cash and cash equivalents	20,827,000		(65,513,000)
Cash and cash equivalents at beginning of year	255,399,000		281,409,000
Cash and cash equivalents at end of period	276,226,000		215,896,000
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the operating partnership relating to the investment in unconsolidated joint ventures	51,647,000		0
Redemption of units in the operating partnership	11,795,000		37,992,000
Derivative instruments at fair value	7,701,000		2,000,000
Exchange of debt investment for equity in joint venture	68,581,000		10,151,000
Transfer of restricted cash to operating cash and cash equivalents as a result of sale	0		21,578,000
Acquisition of subsidiary interest from noncontrolling interest	0		20,630,000
Tenant improvements and capital expenditures payable	11,637,000		17,661,000
Transfer of assets to assets held for sale	1,931,217,000		420,569,000
Transfer of liabilities related to assets held for sale	1,612,008,000		178,252,000
Deferred leasing payable	1,222,000		5,525,000
Removal of fully depreciated commercial real estate properties	13,471,000		0
Preferred Units
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of preferred units relating to the real estate acquisition	22,793,000		53,808,000
Preferred Units | SL Green Operating Partnership
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of preferred units relating to the real estate acquisition	$ 22,793,000		$ 53,808,000

[1] Included in Other non-cash adjustments is $172.4 million for the six months ended June 30, 2016 for the amortization of the below-market lease at 388-390 Greenwich Street as a result of the tenant exercising their option to purchase the property and entering into an agreement to accelerate the sale