Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Operating Activities
Net income	$ 106,921	$ 182,243
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	264,833	249,950
Depreciable real estate reserves	2,150	0
Equity in net income from unconsolidated joint ventures	(4,251)	(80,988)
Distributions of cumulative earnings from unconsolidated joint ventures	21,723	84,182
Purchase price fair value adjustment	2,305	0
Equity in net loss (gain) on sale of interest in unconsolidated joint venture/real estate	3,937	(17,776)
Gain on sale of discontinued operations	(14,900)	(6,627)
Loan loss and other investment reserves, net of recoveries	0	564
Gain on sale of investments in marketable securities	0	(2,237)
Loss on early extinguishment of debt	10,968	0
Deferred rents receivable	(44,021)	(50,910)
Other non-cash adjustments	(31,808)	(864)
Changes in operating assets and liabilities:
Restricted cash — operations	1,254	(12,557)
Tenant and other receivables	(3,018)	(8,500)
Related party receivables	(187)	(3,792)
Deferred lease costs	(28,502)	(37,885)
Other assets	(23,316)	(44,915)
Accounts payable, accrued expenses and other liabilities	23,635	11,309
Deferred revenue and land leases payable	22,731	8,997
Net cash provided by operating activities	310,454	270,194
Investing Activities
Acquisitions of real estate property	(58,185)	(405,318)
Additions to land, buildings and improvements	(108,849)	(107,425)
Escrowed cash — capital improvements/acquisition	(246,682)	(68,692)
Investments in unconsolidated joint ventures	(120,130)	(159,524)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	19,795	48,510
Net proceeds from disposition of real estate/joint venture interest	218,701	70,367
Other investments	(26,003)	(28,911)
Debt and preferred equity and other investments, net of repayments/participations	78,888	(172,411)
Net cash used in investing activities	(242,465)	(823,404)
Financing Activities
Proceeds from mortgages and other loans payable	980,333	1,113,500
Repayments of mortgages and other loans payable	(1,027,201)	(484,518)
Proceeds from credit facility and senior unsecured notes	844,000	813,339
Repayments of credit facility and senior unsecured notes	(578,970)	(1,065,793)
Proceeds from stock options exercised and DRIP issuance	10,452	112,447
Net proceeds from sale of common stock/preferred stock	41,758	423,544
Redemption of preferred stock	(192,500)	(200,013)
Sale or purchase of treasury stock	6,089	(11,197)
Distributions to noncontrolling interests in other partnerships	(11,809)	(15,622)
Contributions from noncontrolling interests in other partnerships	3,781	19,181
Distributions to noncontrolling interests in the Operating Partnership	(2,695)	(2,385)
Dividends paid on common and preferred stock	(113,192)	(91,272)
Deferred loan costs and capitalized lease obligations	(8,921)	(33,830)
Net cash (used in) provided by financing activities	(48,875)	577,381
Net increase in cash and cash equivalents	19,114	24,171
Cash and cash equivalents at beginning of period	189,984	138,192
Cash and cash equivalents at end of period	209,098	162,363
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Issuance of common stock as deferred compensation	434	631
Issuance of units in the Operating Partnership	14,270	40,542
Redemption of units in the Operating Partnership	17,287	17,467
Derivative instruments at fair value	494	375
Assignment of debt investment to joint venture	0	25,362
Mortgage assigned upon asset sale	0	59,099
Tenant improvements and capital expenditures payable	9,855	10,056
Assumption of mortgage loans	84,642	0
Fair value adjustment to noncontrolling interest in the Operating Partnership	38,452	44,893
Accrued acquisition liabilities	0	4,372
Deferred leasing payable	2,849	509
Capital leased asset	9,992	0
Transfer to net assets held for sale	0	86,339
Transfer to liabilities related to net assets held for sale	0	62,792
Repayment of mezzanine loan	0	3,750
Redemption of Series E units	0	31,698
Repayment of financing receivable	0	28,195
Consolidation of real estate investment	90,934	0
Investment in joint venture	0	5,135
SL Green Operating Partnership
Operating Activities
Net income	106,921	182,243
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	264,833	249,950
Depreciable real estate reserves	2,150	0
Equity in net income from unconsolidated joint ventures	(4,251)	(80,988)
Distributions of cumulative earnings from unconsolidated joint ventures	21,723	84,182
Purchase price fair value adjustment	2,305	0
Equity in net loss (gain) on sale of interest in unconsolidated joint venture/real estate	3,937	(17,776)
Gain on sale of discontinued operations	(14,900)	(6,627)
Loan loss and other investment reserves, net of recoveries	0	564
Gain on sale of investments in marketable securities	0	(2,237)
Loss on early extinguishment of debt	10,968	0
Deferred rents receivable	(44,021)	(50,910)
Other non-cash adjustments	(31,808)	(864)
Changes in operating assets and liabilities:
Restricted cash — operations	1,254	(12,557)
Tenant and other receivables	(3,018)	(8,500)
Related party receivables	(187)	(3,792)
Deferred lease costs	(28,502)	(37,885)
Other assets	(23,316)	(44,915)
Accounts payable, accrued expenses and other liabilities	23,635	11,309
Deferred revenue and land leases payable	22,731	8,997
Net cash provided by operating activities	310,454	270,194
Investing Activities
Acquisitions of real estate property	(58,185)	(405,318)
Additions to land, buildings and improvements	(108,849)	(107,425)
Escrowed cash — capital improvements/acquisition	(246,682)	(68,692)
Investments in unconsolidated joint ventures	(120,130)	(159,524)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	19,795	48,510
Net proceeds from disposition of real estate/joint venture interest	218,701	70,367
Other investments	(26,003)	(28,911)
Debt and preferred equity and other investments, net of repayments/participations	78,888	(172,411)
Net cash used in investing activities	(242,465)	(823,404)
Financing Activities
Proceeds from mortgages and other loans payable	980,333	1,113,500
Repayments of mortgages and other loans payable	(1,027,201)	(484,518)
Proceeds from credit facility and senior unsecured notes	844,000	813,339
Repayments of credit facility and senior unsecured notes	(578,970)	(1,065,793)
Proceeds from stock options exercised and DRIP issuance	10,452	112,447
Net proceeds from sale of common stock/preferred stock	41,758	423,544
Redemption of preferred stock	(192,500)	(200,013)
Sale or purchase of treasury stock	6,089	(11,197)
Distributions to noncontrolling interests in other partnerships	(11,809)	(15,622)
Contributions from noncontrolling interests in other partnerships	3,781	19,181
Dividends paid on common and preferred stock	(115,887)	(93,657)
Deferred loan costs and capitalized lease obligations	(8,921)	(33,830)
Net cash (used in) provided by financing activities	(48,875)	577,381
Net increase in cash and cash equivalents	19,114	24,171
Cash and cash equivalents at beginning of period	189,984	138,192
Cash and cash equivalents at end of period	209,098	162,363
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Issuance of common stock as deferred compensation	434	631
Issuance of units in the Operating Partnership	14,270	40,542
Redemption of units in the Operating Partnership	17,287	17,467
Derivative instruments at fair value	494	375
Assignment of debt investment to joint venture	0	25,362
Mortgage assigned upon asset sale	0	59,099
Tenant improvements and capital expenditures payable	9,855	10,056
Assumption of mortgage loans	84,642	0
Accrued acquisition liabilities	0	4,372
Deferred leasing payable	2,849	509
Capital leased asset	9,992	0
Transfer to net assets held for sale	0	86,339
Transfer to liabilities related to net assets held for sale	0	62,792
Repayment of mezzanine loan	0	3,750
Redemption of Series E units	0	31,698
Repayment of financing receivable	0	28,195
Consolidation of real estate investment	90,934	0
Investment in joint venture	$ 0	$ 5,135