Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities
Net income	$ 317,459	$ 545,863	$ 151,283
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	588,238	400,001	357,599
Equity in net income from unconsolidated joint ventures	(13,028)	(26,537)	(9,921)
Distributions of cumulative earnings from unconsolidated joint ventures	40,759	28,859	34,997
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(15,844)	(123,253)	(3,601)
Purchase price fair value adjustment	(40,078)	(71,446)	2,305
Depreciable real estate reserves	19,226	0	2,150
Gain on sale of real estate	(175,974)	0	0
Gain on sale of discontinued operations	(14,122)	(163,059)	(14,900)
Gain on sale of investments in marketable securities	0	(3,895)	0
Loss on early extinguishment of debt	49	32,365	10,963
Deferred rents receivable	(136,924)	(56,362)	(56,739)
Other non-cash adjustments	(20,671)	(28,559)	(37,843)
Changes in operating assets and liabilities:
Restricted cash—operations	11,289	861	2,037
Tenant and other receivables	(6,405)	1,978	(7,570)
Related party receivables	1,278	(3,673)	(917)
Deferred lease costs	(61,005)	(53,333)	(52,228)
Other assets	18,501	9,340	2,904
Accounts payable, accrued expenses and other liabilities and security deposits	8,634	(7,796)	(1,473)
Deferred revenue and land leases payable	5,102	9,027	7,157
Net cash provided by operating activities	526,484	490,381	386,203
Investing Activities
Acquisitions of real estate property	(2,653,311)	(1,039,530)	(594,595)
Additions to land, buildings and improvements	(406,442)	(369,887)	(196,571)
Escrowed cash—capital improvements/acquisition deposits/deferred purchase price	(101,000)	(8,461)	(7,672)
Investments in unconsolidated joint ventures	(161,712)	(382,010)	(150,274)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	98,639	236,181	42,720
Proceeds from disposition of real estate/joint venture interest	1,216,785	820,599	227,615
Proceeds from sale of marketable securities	1,426	8,248	2,370
Purchases of marketable securities	(7,769)	(14,364)	(11,493)
Other investments	(15,806)	(7,448)	(43,163)
Origination of debt and preferred equity investments	(756,939)	(617,090)	(555,137)
Repayments or redemption of debt and preferred equity investments	520,218	576,927	657,765
Net cash used in investing activities	(2,265,911)	(796,835)	(628,435)
Financing Activities
Proceeds from mortgages and other loans payable	1,849,293	2,151,603	1,257,172
Repayments of mortgages and other loans payable	(781,236)	(2,201,999)	(1,085,220)
Proceeds from revolving credit facility and senior unsecured notes	2,515,000	1,908,000	1,164,000
Repayments of revolving credit facility and senior unsecured notes	(1,706,007)	(1,386,588)	(1,020,215)
Payments of debt extinguishment costs	0	(50,150)	0
Proceeds from stock options exercised and DRIP issuance	115,917	25,275	12,971
Proceeds from sale of common stock	124,761	185,321	290,699
Redemption of preferred stock	(200)	(2,000)	(192,533)
Sale or purchase of treasury stock	0	0	7,120
Distributions to noncontrolling interests in other partnerships	(119,784)	(7,019)	(14,623)
Contributions from noncontrolling interests in other partnerships	12,674	30,675	8,164
Distributions to noncontrolling interests in the Operating Partnership	(9,710)	(7,849)	(4,146)
Dividends/Distributions paid on common and preferred stock/units	(257,378)	(206,974)	(148,407)
Other obligations related to mortgage loan participations	25,000	0	0
Deferred loan costs and capitalized lease obligation	(54,913)	(57,124)	(16,042)
Net cash provided by financing activities	1,713,417	381,171	258,940
Net (decrease) increase in cash and cash equivalents	(26,010)	74,717	16,708
Cash and cash equivalents at beginning of year	281,409	206,692	189,984
Cash and cash equivalents at end of period	255,399	281,409	206,692
Supplemental Cash Flow Information [Abstract]
Interest paid	345,110	348,230	325,903
Income taxes paid	3,882	4,056	2,666
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of common stock as deferred compensation	243	1,601	164
Issuance of units in the operating partnership	30,506	56,469	24,750
Redemption of units in the operating partnership	55,697	31,653	17,287
Derivative instruments at fair value	1,816	11,230	636
Exchange of debt investment for equity in joint venture	10,151	0	0
Transfer of restricted cash to operating cash and cash equivalents as a result of sale	21,578	0	0
Acquisition of subsidiary interest from noncontrolling interest	20,630	0	0
Tenant improvements and capital expenditures payable	7,755	9,408	502
Mortgage assigned to joint venture	0	150,000	0
Fair value adjustment to noncontrolling interest in operating partnership	20,915	168,439	45,618
Assumption of mortgage loan	112,795	16,000	84,642
Investment in Joint Venture	0	88,957	0
Capital lease assets	20,000	0	9,992
Reclass of development costs from other assets to real estate	47,519	0	0
Deconsolidation of a subsidiary	27,435	112,095	0
Transfer of assets to assets held for sale	34,981	462,430	0
Transfer of liabilities related to assets held for sale	29,000	266,873	0
Transfer of financing receivable to debt investment	0	19,675	0
Deferred leasing payable	7,832	8,667	5,024
Consolidation of real estate investment	158,566	1,316,591	90,934
Removal of fully depreciated commercial real estate properties	241,910	0	0
Issuance of SLG's common stock to a consolidated joint venture	10,000	0	0
Contribution to consolidated joint venture by noncontrolling interest	22,504	0	0
SL Green Operating Partnership
Operating Activities
Net income	317,459	545,863	151,283
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	588,238	400,001	357,599
Equity in net income from unconsolidated joint ventures	(13,028)	(26,537)	(9,921)
Distributions of cumulative earnings from unconsolidated joint ventures	40,759	28,859	34,997
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(15,844)	(123,253)	(3,601)
Purchase price fair value adjustment	(40,078)	(71,446)	2,305
Depreciable real estate reserves	19,226	0	2,150
Gain on sale of real estate	(175,974)	0	0
Gain on sale of discontinued operations	(14,122)	(163,059)	(14,900)
Gain on sale of investments in marketable securities	0	(3,895)	0
Loss on early extinguishment of debt	49	32,365	10,963
Deferred rents receivable	(136,924)	(56,362)	(56,739)
Other non-cash adjustments	(20,671)	(28,559)	(37,843)
Changes in operating assets and liabilities:
Restricted cash—operations	11,289	861	2,037
Tenant and other receivables	(6,405)	1,978	(7,570)
Related party receivables	1,278	(3,673)	(917)
Deferred lease costs	(61,005)	(53,333)	(52,228)
Other assets	18,501	9,340	2,904
Accounts payable, accrued expenses and other liabilities and security deposits	8,634	(7,796)	(1,473)
Deferred revenue and land leases payable	5,102	9,027	7,157
Net cash provided by operating activities	526,484	490,381	386,203
Investing Activities
Acquisitions of real estate property	(2,653,311)	(1,039,530)	(594,595)
Additions to land, buildings and improvements	(406,442)	(369,887)	(196,571)
Escrowed cash—capital improvements/acquisition deposits/deferred purchase price	(101,000)	(8,461)	(7,672)
Investments in unconsolidated joint ventures	(161,712)	(382,010)	(150,274)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	98,639	236,181	42,720
Proceeds from disposition of real estate/joint venture interest	1,216,785	820,599	227,615
Proceeds from sale of marketable securities	1,426	8,248	2,370
Purchases of marketable securities	(7,769)	(14,364)	(11,493)
Other investments	(15,806)	(7,448)	(43,163)
Origination of debt and preferred equity investments	(756,939)	(617,090)	(555,137)
Repayments or redemption of debt and preferred equity investments	520,218	576,927	657,765
Net cash used in investing activities	(2,265,911)	(796,835)	(628,435)
Financing Activities
Proceeds from mortgages and other loans payable	1,849,293	2,151,603	1,257,172
Repayments of mortgages and other loans payable	(781,236)	(2,201,999)	(1,085,220)
Proceeds from revolving credit facility and senior unsecured notes	2,515,000	1,908,000	1,164,000
Repayments of revolving credit facility and senior unsecured notes	(1,706,007)	(1,386,588)	(1,020,215)
Payments of debt extinguishment costs	0	(50,150)	0
Proceeds from stock options exercised and DRIP issuance	115,917	25,275	12,971
Proceeds from sale of common stock	124,761	185,321	290,699
Redemption of preferred stock	(200)	(2,000)	(192,533)
Sale or purchase of treasury stock	0	0	7,120
Distributions to noncontrolling interests in other partnerships	(119,784)	(7,019)	(14,623)
Contributions from noncontrolling interests in other partnerships	12,674	30,675	8,164
Dividends/Distributions paid on common and preferred stock/units	(267,088)	(214,823)	(152,553)
Other obligations related to mortgage loan participations	25,000	0	0
Deferred loan costs and capitalized lease obligation	(54,913)	(57,124)	(16,042)
Net cash provided by financing activities	1,713,417	381,171	258,940
Net (decrease) increase in cash and cash equivalents	(26,010)	74,717	16,708
Cash and cash equivalents at beginning of year	281,409	206,692	189,984
Cash and cash equivalents at end of period	255,399	281,409	206,692
Supplemental Cash Flow Information [Abstract]
Interest paid	345,110	348,230	325,903
Income taxes paid	3,882	4,056	2,666
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of common stock as deferred compensation	243	1,601	164
Issuance of units in the operating partnership	30,506	56,469	24,750
Redemption of units in the operating partnership	55,697	31,653	17,287
Derivative instruments at fair value	1,816	11,230	636
Exchange of debt investment for equity in joint venture	10,151	0	0
Transfer of restricted cash to operating cash and cash equivalents as a result of sale	21,578	0	0
Acquisition of subsidiary interest from noncontrolling interest	20,630	0	0
Tenant improvements and capital expenditures payable	7,755	9,408	502
Mortgage assigned to joint venture	0	150,000	0
Fair value adjustment to noncontrolling interest in operating partnership	20,915	168,439	45,618
Assumption of mortgage loan	112,795	16,000	84,642
Investment in Joint Venture	0	88,957	0
Capital lease assets	20,000	0	9,992
Reclass of development costs from other assets to real estate	47,519	0	0
Deconsolidation of a subsidiary	27,435	112,095	0
Transfer of assets to assets held for sale	34,981	462,430	0
Transfer of liabilities related to assets held for sale	29,000	266,873	0
Transfer of financing receivable to debt investment	0	19,675	0
Deferred leasing payable	7,832	8,667	5,024
Consolidation of real estate investment	158,566	1,316,591	90,934
Removal of fully depreciated commercial real estate properties	241,910	0	0
Issuance of SLG's common stock to a consolidated joint venture	10,000	0	0
Contribution to consolidated joint venture by noncontrolling interest	22,504	0	0
Common Stock
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition	2,228	0	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	2,228	0	0
Preferred Units
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units relating to the real estate acquisition	211,601	0	0
Issuance of preferred units (Stonehenge)	0	27,565	0
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	211,601	0	0
Issuance of preferred units (Stonehenge)	$ 0	$ 27,565	$ 0