Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Operating Activities
Net income	$ 203,210	$ 480,538
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	473,817	295,877
Equity in net income from unconsolidated joint ventures	(10,651)	(20,781)
Distributions of cumulative earnings from unconsolidated joint ventures	33,141	23,065
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(16,050)	(122,580)
Purchase price fair value adjustment	0	(71,446)
Depreciable real estate reserves	19,226	0
Gain on sale of real estate	(159,704)	0
Gain on sale of discontinued operations	(12,983)	(144,242)
Loss on early extinguishment of debt	49	25,500
Deferred rents receivable	(99,015)	(43,736)
Other non-cash adjustments	(16,140)	(25,705)
Changes in operating assets and liabilities:
Restricted cash—operations	(23,437)	(7,124)
Tenant and other receivables	(8,498)	(7,336)
Related party receivables	646	(5,200)
Deferred lease costs	(46,673)	(17,544)
Other assets	(43,736)	(23,133)
Accounts payable, accrued expenses and other liabilities and security deposits	6,119	17,445
Deferred revenue and land leases payable	23,678	23,608
Net cash provided by operating activities	322,999	377,206
Investing Activities
Acquisitions of real estate property	(2,574,687)	(711,437)
Additions to land, buildings and improvements	(219,760)	(282,947)
Escrowed cash—capital improvements/acquisition deposits/deferred purchase price	(117,026)	(67,868)
Investments in unconsolidated joint ventures	(127,783)	(217,187)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	89,059	158,809
Proceeds from disposition of real estate/joint venture interest	1,072,175	357,426
Proceeds from sale of marketable securities	432	3,669
Purchases of marketable securities	(7,769)	(10,025)
Other investments	(11,894)	15,980
Origination of debt and preferred equity investments	(461,257)	(421,003)
Repayments or redemption of debt and preferred equity investments	372,084	349,320
Net cash used in investing activities	(1,986,426)	(825,263)
Financing Activities
Proceeds from mortgages and other loans payable	1,706,018	2,001,603
Repayments of mortgages and other loans payable	(681,286)	(1,688,466)
Proceeds from revolving credit facility and senior unsecured notes	2,130,000	1,136,400
Repayments of revolving credit facility and senior unsecured notes	(1,466,007)	(805,988)
Payments of debt extinguishment costs	0	(23,332)
Proceeds from stock options exercised and DRSSP issuance	112,399	20,549
Proceeds from sale of common stock	124,794	42,698
Redemption of preferred unit	(200)	0
Distributions to noncontrolling interests in other partnerships	(113,595)	(5,745)
Contributions from noncontrolling interests in other partnerships	11,931	27,933
Distributions to noncontrolling interests in the Operating Partnership	(7,017)	(5,482)
Dividends/Distributions paid on common and preferred stock/units	(191,920)	(154,907)
Other obligations related to mortgage loan participations	25,000	0
Deferred loan costs and capitalized lease obligation	(23,739)	(50,378)
Net cash provided by financing activities	1,626,378	494,885
Net (decrease) increase in cash and cash equivalents	(37,049)	46,828
Cash and cash equivalents at beginning of year	281,409	206,692
Cash and cash equivalents at end of period	244,360	253,520
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of common stock as deferred compensation	1,744	1,503
Issuance of units in the Operating Partnership	27,898	22,862
Redemption of units in the Operating Partnership	41,605	26,392
Derivative instruments at fair value	5,459	12,713
Exchange of debt investment for equity in joint venture	10,151	0
Transfer of restricted cash to operating cash and cash equivalents as a result of sale	21,578	0
Acquisition of subsidiary interest from noncontrolling interest	20,630	0
Tenant improvements and capital expenditures payable	14,470	8,456
Fair value adjustment to noncontrolling interest in the Operating Partnership	31,664	108,453
Capital lease asset	20,000	0
Reclass of development costs from other assets to real estate	47,519	0
Transfer to net assets held for sale	117,885	753,457
Transfer to liabilities related to net assets held for sale	94	461,891
Transfer of financing receivable to debt investment	0	19,675
Deferred leasing payable	6,176	13,086
Consolidation of real estate	0	1,316,591
Issuance of common stock to consolidated joint venture	10,000	0
Contribution to consolidated joint venture by noncontrolling interest	22,504	0
Receivable from sale of unconsolidated joint venture interests	15,129	0
SL Green Operating Partnership
Operating Activities
Net income	203,210	480,538
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	473,817	295,877
Equity in net income from unconsolidated joint ventures	(10,651)	(20,781)
Distributions of cumulative earnings from unconsolidated joint ventures	33,141	23,065
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(16,050)	(122,580)
Purchase price fair value adjustment	0	(71,446)
Depreciable real estate reserves	19,226	0
Gain on sale of real estate	(159,704)	0
Gain on sale of discontinued operations	(12,983)	(144,242)
Loss on early extinguishment of debt	49	25,500
Deferred rents receivable	(99,015)	(43,736)
Other non-cash adjustments	(16,140)	(25,705)
Changes in operating assets and liabilities:
Restricted cash—operations	(23,437)	(7,124)
Tenant and other receivables	(8,498)	(7,336)
Related party receivables	646	(5,200)
Deferred lease costs	(46,673)	(17,544)
Other assets	(43,736)	(23,133)
Accounts payable, accrued expenses and other liabilities and security deposits	6,119	17,445
Deferred revenue and land leases payable	23,678	23,608
Net cash provided by operating activities	322,999	377,206
Investing Activities
Acquisitions of real estate property	(2,574,687)	(711,437)
Additions to land, buildings and improvements	(219,760)	(282,947)
Escrowed cash—capital improvements/acquisition deposits/deferred purchase price	(117,026)	(67,868)
Investments in unconsolidated joint ventures	(127,783)	(217,187)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	89,059	158,809
Proceeds from disposition of real estate/joint venture interest	1,072,175	357,426
Proceeds from sale of marketable securities	432	3,669
Purchases of marketable securities	(7,769)	(10,025)
Other investments	(11,894)	15,980
Origination of debt and preferred equity investments	(461,257)	(421,003)
Repayments or redemption of debt and preferred equity investments	372,084	349,320
Net cash used in investing activities	(1,986,426)	(825,263)
Financing Activities
Proceeds from mortgages and other loans payable	1,706,018	2,001,603
Repayments of mortgages and other loans payable	(681,286)	(1,688,466)
Proceeds from revolving credit facility and senior unsecured notes	2,130,000	1,136,400
Repayments of revolving credit facility and senior unsecured notes	(1,466,007)	(805,988)
Payments of debt extinguishment costs	0	(23,332)
Proceeds from stock options exercised and DRSSP issuance	112,399	20,549
Proceeds from sale of common stock	124,794	42,698
Redemption of preferred unit	(200)	0
Distributions to noncontrolling interests in other partnerships	(113,595)	(5,745)
Contributions from noncontrolling interests in other partnerships	11,931	27,933
Dividends/Distributions paid on common and preferred stock/units	(198,937)	(160,389)
Other obligations related to mortgage loan participations	25,000	0
Deferred loan costs and capitalized lease obligation	(23,739)	(50,378)
Net cash provided by financing activities	1,626,378	494,885
Net (decrease) increase in cash and cash equivalents	(37,049)	46,828
Cash and cash equivalents at beginning of year	281,409	206,692
Cash and cash equivalents at end of period	244,360	253,520
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of common stock as deferred compensation	1,744	1,503
Issuance of units in the Operating Partnership	27,898	22,862
Redemption of units in the Operating Partnership	41,605	26,392
Derivative instruments at fair value	5,459	12,713
Exchange of debt investment for equity in joint venture	10,151	0
Transfer of restricted cash to operating cash and cash equivalents as a result of sale	21,578	0
Acquisition of subsidiary interest from noncontrolling interest	20,630	0
Tenant improvements and capital expenditures payable	14,470	8,456
Capital lease asset	20,000	0
Reclass of development costs from other assets to real estate	47,519	0
Transfer to net assets held for sale	117,885	753,457
Transfer to liabilities related to net assets held for sale	94	461,891
Transfer of financing receivable to debt investment	0	19,675
Deferred leasing payable	6,176	13,086
Consolidation of real estate	0	1,316,591
Deconsolidation of subsidiary	27,435	0
Issuance of common stock to consolidated joint venture	10,000	0
Contribution to consolidated joint venture by noncontrolling interest	22,504	0
Receivable from sale of unconsolidated joint venture interests	15,129	0
Common Stock
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units	2,228	0
Common Stock | SL Green Operating Partnership
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units	2,228	0
Preferred Units
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units	211,601	27,565
Preferred Units | SL Green Operating Partnership
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of stock/units	$ 211,601	$ 27,565