Consolidated Statements of Cash Flows (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Activities
Net income	$ 151,283,000	$ 209,700,000	$ 677,122,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	357,599,000	351,539,000	292,311,000
Equity in net income from unconsolidated joint ventures	(9,921,000)	(76,418,000)	(1,583,000)
Distributions of cumulative earnings from unconsolidated joint ventures	34,997,000	91,145,000	11,185,000
Equity in net gain on sale of interest in unconsolidated joint venture interest/ real estate	(3,601,000)	(37,053,000)	(2,918,000)
Purchase price fair value adjustment	2,305,000	0	(498,195,000)
Depreciable real estate reserves	2,150,000	0	5,789,000
Gain on sale of discontinued operations	(14,900,000)	(6,627,000)	(46,085,000)
Gain on sale of debt securities	0	0	(19,840,000)
Loan loss and other investment reserves, net of recoveries	0	564,000	6,722,000
(Loss) gain on sale of investment in marketable securities	0	4,940,000	4,866,000
Loss (gain) on early extinguishment of debt	(10,963,000)	(6,978,000)	904,000
Deferred rents receivable	(56,739,000)	(66,079,000)	(87,230,000)
Other non-cash adjustments	(37,843,000)	(18,868,000)	523,000
Changes in operating assets and liabilities:
Restricted cash—operations	2,037,000	(13,812,000)	(681,000)
Tenant and other receivables	(7,570,000)	(10,998,000)	(4,720,000)
Related party receivables	(917,000)	(3,529,000)	2,461,000
Deferred lease costs	(52,228,000)	(48,368,000)	(38,412,000)
Other assets	2,904,000	(35,932,000)	4,029,000
Accounts payable, accrued expenses and other liabilities	(1,473,000)	9,389,000	10,704,000
Deferred revenue and land leases payable	7,157,000	62,000	1,706,000
Net cash provided by operating activities	386,203,000	346,753,000	307,118,000
Investing Activities
Acquisitions of real estate property	(594,595,000)	(544,568,000)	(446,756,000)
Additions to land, buildings and improvements	(196,571,000)	(148,148,000)	(159,100,000)
Escrowed cash—capital improvements/acquisition deposits	(7,672,000)	(70,080,000)	29,281,000
Investments in unconsolidated joint ventures	(150,274,000)	(215,174,000)	(109,920,000)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	42,720,000	127,876,000	112,359,000
Net proceeds from disposition of real estate/joint venture interest	227,615,000	178,485,000	160,548,000
Proceeds from sale of marketable securities	(2,370,000)	(11,070,000)	(40,248,000)
Purchases of marketable securities	(11,493,000)	(6,660,000)	(28,570,000)
Other investments	(43,163,000)	(36,750,000)	537,000
Debt and preferred equity and other investments, net of repayments/participations	102,628,000	(459,454,000)	(332,482,000)
Net cash used in investing activities	(628,435,000)	(1,163,403,000)	(733,855,000)
Financing Activities
Proceeds from mortgages and other loans payable	1,257,172,000	1,230,167,000	826,000,000
Repayments of mortgages and other loans payable	(1,085,220,000)	(688,065,000)	(765,378,000)
Proceeds from revolving credit facility and senior unsecured notes	1,164,000,000	1,751,480,000	1,901,068,000
Repayments of revolving credit facility and senior unsecured notes	(1,020,215,000)	(1,581,554,000)	(2,043,144,000)
Proceeds from stock options exercised and DRIP issuance	12,971,000	112,743,000	10,211,000
Net proceeds from sale of common stock	290,699,000	201,279,000	516,168,000
Net proceeds from sale of preferred stock	0	221,965,000	0
Redemption of preferred stock	(192,533,000)	(200,013,000)	0
Sale or purchase of treasury stock	7,120,000	(14,150,000)	(5,486,000)
Distributions to noncontrolling interests in other partnerships	(14,623,000)	(21,946,000)	(143,578,000)
Contributions from noncontrolling interests in other partnerships	8,164,000	25,894,000	0
Distributions to noncontrolling interests in the Operating Partnership	(4,146,000)	(3,296,000)	(727,000)
Dividends paid on common and preferred stock	(148,407,000)	(121,238,000)	(63,866,000)
Other obligations related to mortgage loan participations	0	5,000,000	35,850,000
Deferred loan costs and capitalized lease obligation	(16,042,000)	(49,824,000)	(35,019,000)
Net cash provided by financing activities	258,940,000	868,442,000	232,099,000
Net increase (decrease) in cash and cash equivalents	16,708,000	51,792,000	(194,638,000)
Cash and cash equivalents at beginning of year	189,984,000	138,192,000	332,830,000
Cash and cash equivalents at end of year	206,692,000	189,984,000	138,192,000
Supplemental cash flow disclosures:
Interest paid	325,903,000	322,469,000	277,109,000
Income taxes paid	2,666,000	17,000	138,000
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of common stock as deferred compensation	164,000	722,000	699,000
Redemption of units in the Operating Partnership	17,287,000	87,513,000	865,000
Derivative instruments at fair value	636,000	92,000	1,870,000
Assignment of debt investment to joint venture	0	25,362,000	286,571,000
Mortgage assigned to joint venture	0	0	30,000,000
Tenant improvements and capital expenditures payable	502,000	1,738,000	3,990,000
Fair value adjustment to noncontrolling interest in the Operating Partnership	45,618,000	61,238,000	39,040,000
Accrued acquisition liabilities	0	0	34,500,000
Assumption of mortgage loans	84,642,000	0	943,767,000
Consolidation of real estate investments and other adjustments	90,934,000	0	1,156,929,000
Consolidation of real estate investments—noncontrolling interest in other partnerships	0	0	87,264,000
Repayment of mezzanine loans	0	13,750,000	0
Redemption of Series E units	0	31,698,000	0
Repayment of financing receivable	0	28,195,000	0
Investment in joint venture	0	5,135,000	0
Capital leased asset	9,992,000	28,132,000	0
Deconsolidation of a subsidiary	0	104,107,000	0
Transfer to net assets held for sale	0	4,901,000	0
Transfer to liabilities related to net assets held for sale	0	136,000	0
Issuance of preferred units	0	47,550,000	0
SL Green Operating Partnership
Operating Activities
Net income	151,283,000	209,700,000	677,122,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	357,599,000	351,539,000	292,311,000
Equity in net income from unconsolidated joint ventures	(9,921,000)	(76,418,000)	(1,583,000)
Distributions of cumulative earnings from unconsolidated joint ventures	34,997,000	91,145,000	11,185,000
Equity in net gain on sale of interest in unconsolidated joint venture interest/ real estate	(3,601,000)	(37,053,000)	(2,918,000)
Purchase price fair value adjustment	2,305,000	0	(498,195,000)
Depreciable real estate reserves	2,150,000	0	5,789,000
Gain on sale of discontinued operations	(14,900,000)	(6,627,000)	(46,085,000)
Gain on sale of debt securities	0	0	(19,840,000)
Loan loss and other investment reserves, net of recoveries	0	564,000	6,722,000
(Loss) gain on sale of investment in marketable securities	0	4,940,000	4,866,000
Loss (gain) on early extinguishment of debt	(10,963,000)	(6,978,000)	904,000
Deferred rents receivable	(56,739,000)	(66,079,000)	(87,230,000)
Other non-cash adjustments	(37,843,000)	(18,868,000)	523,000
Changes in operating assets and liabilities:
Restricted cash—operations	2,037,000	(13,812,000)	(681,000)
Tenant and other receivables	(7,570,000)	(10,998,000)	(4,720,000)
Related party receivables	(917,000)	(3,529,000)	2,461,000
Deferred lease costs	(52,228,000)	(48,368,000)	(38,412,000)
Other assets	2,904,000	(35,932,000)	4,029,000
Accounts payable, accrued expenses and other liabilities	(1,473,000)	9,389,000	10,704,000
Deferred revenue and land leases payable	7,157,000	62,000	1,706,000
Net cash provided by operating activities	386,203,000	346,753,000	307,118,000
Investing Activities
Acquisitions of real estate property	(594,595,000)	(544,568,000)	(446,756,000)
Additions to land, buildings and improvements	(196,571,000)	(148,148,000)	(159,100,000)
Escrowed cash—capital improvements/acquisition deposits	(7,672,000)	(70,080,000)	29,281,000
Investments in unconsolidated joint ventures	(150,274,000)	(215,174,000)	(109,920,000)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	42,720,000	127,876,000	112,359,000
Net proceeds from disposition of real estate/joint venture interest	227,615,000	178,485,000	160,548,000
Proceeds from sale of marketable securities	(2,370,000)	(11,070,000)	(40,248,000)
Purchases of marketable securities	(11,493,000)	(6,660,000)	(28,570,000)
Other investments	(43,163,000)	(36,750,000)	537,000
Debt and preferred equity and other investments, net of repayments/participations	102,628,000	(459,454,000)	(332,482,000)
Net cash used in investing activities	(628,435,000)	(1,163,403,000)	(733,855,000)
Financing Activities
Proceeds from mortgages and other loans payable	1,257,172,000	1,230,167,000	826,000,000
Repayments of mortgages and other loans payable	(1,085,220,000)	(688,065,000)	(765,378,000)
Proceeds from revolving credit facility and senior unsecured notes	1,164,000,000	1,751,480,000	1,901,068,000
Repayments of revolving credit facility and senior unsecured notes	(1,020,215,000)	(1,581,554,000)	(2,043,144,000)
Proceeds from stock options exercised and DRIP issuance	12,971,000	112,743,000	10,211,000
Net proceeds from sale of common stock	290,699,000	201,279,000	516,168,000
Net proceeds from sale of preferred stock	0	221,965,000	0
Redemption of preferred stock	(192,533,000)	(200,013,000)	0
Sale or purchase of treasury stock	7,120,000	(14,150,000)	(5,486,000)
Distributions to noncontrolling interests in other partnerships	(14,623,000)	(21,946,000)	(143,578,000)
Contributions from noncontrolling interests in other partnerships	8,164,000	25,894,000	0
Dividends paid on common and preferred stock	(152,553,000)	(124,534,000)	(64,593,000)
Other obligations related to mortgage loan participations	0	5,000,000	35,850,000
Deferred loan costs and capitalized lease obligation	(16,042,000)	(49,824,000)	(35,019,000)
Net cash provided by financing activities	258,940,000	868,442,000	232,099,000
Net increase (decrease) in cash and cash equivalents	16,708,000	51,792,000	(194,638,000)
Cash and cash equivalents at beginning of year	189,984,000	138,192,000	332,830,000
Cash and cash equivalents at end of year	206,692,000	189,984,000	138,192,000
Supplemental cash flow disclosures:
Interest paid	325,903,000	322,469,000	277,109,000
Income taxes paid	2,666,000	17,000	138,000
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of common stock as deferred compensation	164,000	722,000	699,000
Issuance of units in the Operating Partnership	24,750,000	42,239,000	62,443,000
Redemption of units in the Operating Partnership	17,287,000	87,513,000	865,000
Derivative instruments at fair value	636,000	92,000	1,870,000
Assignment of debt investment to joint venture	0	25,362,000	286,571,000
Mortgage assigned to joint venture	0	0	30,000,000
Tenant improvements and capital expenditures payable	502,000	1,738,000	3,990,000
Accrued acquisition liabilities	0	0	34,500,000
Assumption of mortgage loans	84,642,000	0	943,767,000
Assumption of mortgage loans	90,934,000	0	1,156,929,000
Consolidation of real estate investments and other adjustments	0	0	87,264,000
Consolidation of real estate investments—noncontrolling interest in other partnerships	0	13,750,000	0
Repayment of mezzanine loans	0	31,698,000	0
Redemption of Series E units	0	28,195,000	0
Investment in joint venture	0	5,135,000	0
Capital leased asset	9,992,000	28,132,000	0
Deconsolidation of a subsidiary	0	104,107,000	0
Transfer to net assets held for sale	0	4,901,000	0
Transfer to liabilities related to net assets held for sale	0	136,000	0
Issuance of preferred units	$ 0	$ 47,550,000	$ 0