Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Operating Activities
Net income	$ 278,911		$ 317,459	$ 545,863
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	845,605		588,238	400,001
Equity in net income from unconsolidated joint ventures	(11,874)		(13,028)	(26,537)
Distributions of cumulative earnings from unconsolidated joint ventures	24,337		40,759	28,859
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(44,009)		(15,844)	(123,253)
Purchase price fair value adjustment	0		(40,078)	(71,446)
Depreciable real estate reserves	10,387		19,226	0
Gain on sale of real estate	(238,116)		(175,974)	0
Gain on sale of discontinued operations	0		(14,122)	(163,059)
Gain on sale of investments in marketable securities	83		0	(3,895)
Loss on early extinguishment of debt	0		49	32,365
Deferred rents receivable	26,716		(136,924)	(56,362)
Other non-cash adjustments	(150,913)	[1]	(20,671)	(28,559)
Changes in operating assets and liabilities:
Restricted cash—operations	(10,811)		11,289	861
Tenant and other receivables	4,780		(6,405)	1,978
Related party receivables	(5,183)		1,278	(3,673)
Deferred lease costs	(70,707)		(61,005)	(53,333)
Other assets	9,899		18,501	9,340
Accounts payable, accrued expenses and other liabilities and security deposits	(35,628)		8,634	(7,796)
Deferred revenue and land leases payable	1,237		5,102	9,027
Net cash provided by operating activities	634,714		526,484	490,381
Investing Activities
Acquisitions of real estate property	(37,760)		(2,653,311)	(1,039,530)
Additions to land, buildings and improvements	(411,950)		(406,442)	(369,887)
Escrowed cash—capital improvements/acquisition deposits/deferred purchase price	92,374		(101,000)	(8,461)
Investments in unconsolidated joint ventures	(84,456)		(161,712)	(382,010)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	196,211		98,639	236,181
Proceeds from disposition of real estate/joint venture interest	2,469,719		1,216,785	820,599
Proceeds from sale of marketable securities	6,965		1,426	8,248
Purchases of marketable securities	(43,341)		(7,769)	(14,364)
Other investments	7,704		(15,806)	(7,448)
Origination of debt and preferred equity investments	(977,413)		(756,939)	(617,090)
Repayments or redemption of debt and preferred equity investments	904,517		520,218	576,927
Net cash provided by (used in) investing activities	2,122,570		(2,265,911)	(796,835)
Financing Activities
Proceeds from mortgages and other loans payable	408,293		1,849,293	2,151,603
Repayments of mortgages and other loans payable	(1,822,303)		(781,236)	(2,201,999)
Proceeds from revolving credit facility and senior unsecured notes	1,325,300		2,515,000	1,908,000
Repayments of revolving credit facility and senior unsecured notes	(2,334,604)		(1,706,007)	(1,386,588)
Payments of debt extinguishment costs	0		0	(50,150)
Proceeds from stock options exercised and DRIP issuance	15,109		115,917	25,275
Proceeds from sale of common stock	0		124,761	185,321
Redemption of preferred stock	(3,299)		(200)	(2,000)
Distributions to noncontrolling interests in other partnerships	(15,419)		(119,784)	(7,019)
Contributions from noncontrolling interests in other partnerships	2,359		12,674	30,675
Distributions to noncontrolling interests in the Operating Partnership	(12,671)		(9,710)	(7,849)
Dividends/Distributions paid on common and preferred stock/units	(314,079)		(257,378)	(206,974)
Other obligations related to mortgage loan participations	59,150		25,000	0
Deferred loan costs and capitalized lease obligation	(41,076)		(54,913)	(57,124)
Net cash (used in) provided by financing activities	(2,733,240)		1,713,417	381,171
Net increase (decrease) in cash and cash equivalents	24,044		(26,010)	74,717
Cash and cash equivalents at beginning of year	255,399		281,409	206,692
Cash and cash equivalents at end of period	279,443		255,399	281,409
Supplemental Cash Flow Information [Abstract]
Interest paid	344,295		345,110	348,230
Income taxes paid	2,009		3,882	4,056
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the operating partnership	78,495		30,506	56,469
Redemption of units in the operating partnership	31,806		55,697	31,653
Derivative instruments at fair value	31,826		1,816	11,230
Exchange of debt investment for equity in joint venture	68,581		10,151	0
Transfer of restricted cash to operating cash and cash equivalents as a result of sale	0		21,578	0
Acquisition of subsidiary interest from noncontrolling interest	0		20,630	0
Tenant improvements and capital expenditures payable	15,972		7,755	9,408
Mortgage assigned to joint venture	0		0	150,000
Fair value adjustment to noncontrolling interest in operating partnership	4,222		20,915	168,439
Assumption of mortgage loan	0		112,795	16,000
Investment in Joint Venture	0		0	88,957
Capital lease assets	0		20,000	0
Reclass of development costs from other assets to real estate	0		47,519	0
Deconsolidation of a subsidiary	1,226,425		27,435	112,095
Transfer of assets to assets held for sale	2,048,376		34,981	462,430
Transfer of liabilities related to assets held for sale	1,677,528		29,000	266,873
Transfer of financing receivable to debt investment	0		0	19,675
Deferred leasing payable	1,556		7,832	8,667
Consolidation of real estate investment	0		158,566	1,316,591
Removal of fully depreciated commercial real estate properties	31,474		241,910	0
Issuance of SLG's common stock to a consolidated joint venture	114,049		10,000	0
Contribution to consolidated joint venture by noncontrolling interest	0		22,504	0
SL Green Operating Partnership
Operating Activities
Net income	278,911		317,459	545,863
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	845,605		588,238	400,001
Equity in net income from unconsolidated joint ventures	(11,874)		(13,028)	(26,537)
Distributions of cumulative earnings from unconsolidated joint ventures	24,337		40,759	28,859
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(44,009)		(15,844)	(123,253)
Purchase price fair value adjustment	0		(40,078)	(71,446)
Depreciable real estate reserves	10,387		19,226	0
Gain on sale of real estate	(238,116)		(175,974)	0
Gain on sale of discontinued operations	0		(14,122)	(163,059)
Gain on sale of investments in marketable securities	83		0	(3,895)
Loss on early extinguishment of debt	0		49	32,365
Deferred rents receivable	26,716		(136,924)	(56,362)
Other non-cash adjustments	(150,913)	[1]	(20,671)	(28,559)
Changes in operating assets and liabilities:
Restricted cash—operations	(10,811)		11,289	861
Tenant and other receivables	4,780		(6,405)	1,978
Related party receivables	(5,183)		1,278	(3,673)
Deferred lease costs	(70,707)		(61,005)	(53,333)
Other assets	9,899		18,501	9,340
Accounts payable, accrued expenses and other liabilities and security deposits	(35,628)		8,634	(7,796)
Deferred revenue and land leases payable	1,237		5,102	9,027
Net cash provided by operating activities	634,714		526,484	490,381
Investing Activities
Acquisitions of real estate property	(37,760)		(2,653,311)	(1,039,530)
Additions to land, buildings and improvements	(411,950)		(406,442)	(369,887)
Escrowed cash—capital improvements/acquisition deposits/deferred purchase price	92,374		(101,000)	(8,461)
Investments in unconsolidated joint ventures	(84,456)		(161,712)	(382,010)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	196,211		98,639	236,181
Proceeds from disposition of real estate/joint venture interest	2,469,719		1,216,785	820,599
Proceeds from sale of marketable securities	6,965		1,426	8,248
Purchases of marketable securities	(43,341)		(7,769)	(14,364)
Other investments	7,704		(15,806)	(7,448)
Origination of debt and preferred equity investments	(977,413)		(756,939)	(617,090)
Repayments or redemption of debt and preferred equity investments	904,517		520,218	576,927
Net cash provided by (used in) investing activities	2,122,570		(2,265,911)	(796,835)
Financing Activities
Proceeds from mortgages and other loans payable	408,293		1,849,293	2,151,603
Repayments of mortgages and other loans payable	(1,822,303)		(781,236)	(2,201,999)
Proceeds from revolving credit facility and senior unsecured notes	1,325,300		2,515,000	1,908,000
Repayments of revolving credit facility and senior unsecured notes	(2,334,604)		(1,706,007)	(1,386,588)
Payments of debt extinguishment costs	0		0	(50,150)
Proceeds from stock options exercised and DRIP issuance	15,109		115,917	25,275
Proceeds from sale of common stock	0		124,761	185,321
Redemption of preferred stock	(3,299)		(200)	(2,000)
Distributions to noncontrolling interests in other partnerships	(15,419)		(119,784)	(7,019)
Contributions from noncontrolling interests in other partnerships	2,359		12,674	30,675
Dividends/Distributions paid on common and preferred stock/units	(326,750)		(267,088)	(214,823)
Other obligations related to mortgage loan participations	59,150		25,000	0
Deferred loan costs and capitalized lease obligation	(41,076)		(54,913)	(57,124)
Net cash (used in) provided by financing activities	(2,733,240)		1,713,417	381,171
Net increase (decrease) in cash and cash equivalents	24,044		(26,010)	74,717
Cash and cash equivalents at beginning of year	255,399		281,409	206,692
Cash and cash equivalents at end of period	279,443		255,399	281,409
Supplemental Cash Flow Information [Abstract]
Interest paid	344,295		345,110	348,230
Income taxes paid	2,009		3,882	4,056
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the operating partnership	78,495		30,506	56,469
Redemption of units in the operating partnership	31,806		55,697	31,653
Derivative instruments at fair value	31,826		1,816	11,230
Exchange of debt investment for equity in joint venture	68,581		10,151	0
Transfer of restricted cash to operating cash and cash equivalents as a result of sale	0		21,578	0
Acquisition of subsidiary interest from noncontrolling interest	0		20,630	0
Tenant improvements and capital expenditures payable	15,972		7,755	9,408
Mortgage assigned to joint venture	0		0	150,000
Fair value adjustment to noncontrolling interest in operating partnership	4,222		20,915	168,439
Assumption of mortgage loan	0		112,795	16,000
Investment in Joint Venture	0		0	88,957
Capital lease assets	0		20,000	0
Reclass of development costs from other assets to real estate	0		47,519	0
Deconsolidation of a subsidiary	1,226,425		27,435	112,095
Transfer of assets to assets held for sale	2,048,376		34,981	462,430
Transfer of liabilities related to assets held for sale	1,677,528		29,000	266,873
Transfer of financing receivable to debt investment	0		0	19,675
Deferred leasing payable	1,556		7,832	8,667
Consolidation of real estate investment	0		158,566	1,316,591
Removal of fully depreciated commercial real estate properties	31,474		241,910	0
Issuance of SLG's common stock to a consolidated joint venture	114,049		10,000	0
Contribution to consolidated joint venture by noncontrolling interest	0		22,504	0
Common Stock
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition	0		2,228	0
Common Stock | SL Green Operating Partnership
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition	0		2,228	0
Preferred Units
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition	22,793		211,601	27,565
Preferred Units | SL Green Operating Partnership
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition	$ 22,793		$ 211,601	$ 27,565

[1] Included in Other non-cash adjustments is $172.4 million for the year ended December 31, 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.