Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Operating Activities
Net income	$ 173,741	$ 115,899	$ 226,510	$ 229,722
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			143,258	144,385
Equity in net loss (income) from unconsolidated joint ventures	7,546	(4,702)	12,780	(8,738)
Distributions of cumulative earnings from unconsolidated joint ventures			566	9,889
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(59,015)	(72,025)	(76,181)	(65,585)
Purchase price and other fair value adjustments			(65,590)	(60,442)
Loss (gain) on sale of real estate, net			1,049	(8,731)
Loan loss reserves and other investment reserves, net of recoveries			0		$ 6,839
Deferred rents receivable			(5,674)	(4,369)
Other non-cash adjustments			5,431	9,404
Changes in operating assets and liabilities:
Tenant and other receivables			(1,109)	(397)
Related party receivables			4,481	(1,116)
Deferred lease costs			(32,183)	(17,469)
Other assets			(295)	(4,329)
Accounts payable, accrued expenses, other liabilities and security deposits			5,299	22,867
Deferred revenue and land leases payable			(427)	1,121
Net cash provided by operating activities			217,915	246,212
Investing Activities
Acquisitions of real estate property			(262,343)	(9,733)
Additions to land, buildings and improvements			(93,013)	(96,577)
Acquisition deposits and deferred purchase price			(228)	(1,520)
Investments in unconsolidated joint ventures			(97,447)	(254,305)
Distributions in excess of cumulative earnings from unconsolidated joint ventures			45,241	178,892
Net proceeds from disposition of real estate/joint venture interest			138,526	760,335
Other investments			(1,056)	(22,790)
Origination of debt and preferred equity investments			(523,476)	(603,575)
Repayments or redemption of debt and preferred equity investments			327,392	317,337
Net cash (used in) provided by investing activities			(466,404)	268,064
Financing Activities
Proceeds from mortgages and other loans payable			427,352	210,575
Repayments of mortgages and other loans payable			(43,630)	(22,864)
Proceeds from revolving credit facility and senior unsecured notes			940,000	1,475,000
Repayments of revolving credit facility and senior unsecured notes			(770,000)	(1,155,000)
Proceeds from stock options exercised and DRSPP issuance			263	5,701
Repurchase of common stock			(109,313)	(724,696)
Redemption of preferred units			(15,142)	(350)
Redemption of OP units			(15,851)	0
Distributions to noncontrolling interests in other partnerships			(271)	(724)
Contributions from noncontrolling interests in other partnerships			2,469	1,828
Acquisition of subsidiary interest from noncontrolling interest			(25,791)	0
Distributions to noncontrolling interests in the Operating Partnership			(7,353)	(7,712)
Dividends / Distributions paid on common and preferred stock / units			(154,460)	(160,699)
Other obligations related to loan participations			0	(3)
Tax withholdings related to restricted share awards			(3,126)	(3,842)
Deferred loan costs and capitalized lease obligation			(14,624)	(1,536)
Net cash provided by (used in) financing activities			210,523	(384,322)
Net (decrease) increase in cash, cash equivalents, and restricted cash			(37,966)	129,954
Cash, cash equivalents, and restricted cash at end of period	241,147	379,980	241,147	379,980
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the Operating Partnership			0	15,448
Conversion of units in the Operating Partnership for common stock			446	1,560
Derivative instruments at fair value			0	6,937
Tenant improvements and capital expenditures payable			9,021	16,534
Fair value adjustment to noncontrolling interest in Operating Partnership			43,835	4,493
Deconsolidation of subsidiaries			0	298,403
Transfer of assets related to assets held for sale			0	593,995
Transfer of liabilities related to assets held for sale			0	265,538
Removal of fully depreciated commercial real estate properties			5,728	110,594
Contribution to consolidated joint venture by noncontrolling interest		0	48,223
Share repurchase payable			0	31,605
Recognition of right of use assets and related lease liabilities			389,120	0
Cash and cash equivalents						$ 148,978	$ 129,475	$ 287,240
Restricted cash						92,169	149,638	92,740
Total cash, cash equivalents, and restricted cash	241,147	379,980	241,147	379,980		241,147		379,980
SL Green Operating Partnership
Operating Activities
Net income	173,741	115,899	226,510	229,722
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			143,258	144,385
Equity in net loss (income) from unconsolidated joint ventures	7,546	(4,702)	12,780	(8,738)
Distributions of cumulative earnings from unconsolidated joint ventures			566	9,889
Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate	(59,015)	(72,025)	(76,181)	(65,585)
Purchase price and other fair value adjustments			(65,590)	(60,442)
Loss (gain) on sale of real estate, net			1,049	(8,731)
Deferred rents receivable			(5,674)	(4,369)
Other non-cash adjustments			5,431	9,404
Changes in operating assets and liabilities:
Tenant and other receivables			(1,109)	(397)
Related party receivables			4,481	(1,116)
Deferred lease costs			(32,183)	(17,469)
Other assets			(295)	(4,329)
Accounts payable, accrued expenses, other liabilities and security deposits			5,299	22,867
Deferred revenue and land leases payable			(427)	1,121
Net cash provided by operating activities			217,915	246,212
Investing Activities
Acquisitions of real estate property			(262,343)	(9,733)
Additions to land, buildings and improvements			(93,013)	(96,577)
Acquisition deposits and deferred purchase price			(228)	(1,520)
Investments in unconsolidated joint ventures			(97,447)	(254,305)
Distributions in excess of cumulative earnings from unconsolidated joint ventures			45,241	178,892
Net proceeds from disposition of real estate/joint venture interest			138,526	760,335
Other investments			(1,056)	(22,790)
Origination of debt and preferred equity investments			(523,476)	(603,575)
Repayments or redemption of debt and preferred equity investments			327,392	317,337
Net cash (used in) provided by investing activities			(466,404)	268,064
Financing Activities
Proceeds from mortgages and other loans payable			427,352	210,575
Repayments of mortgages and other loans payable			(43,630)	(22,864)
Proceeds from revolving credit facility and senior unsecured notes			940,000	1,475,000
Repayments of revolving credit facility and senior unsecured notes			(770,000)	(1,155,000)
Proceeds from stock options exercised and DRSPP issuance			263	5,701
Repurchase of common stock			(109,313)	(724,696)
Redemption of preferred units			(15,142)	(350)
Redemption of OP units			(15,851)	0
Distributions to noncontrolling interests in other partnerships			(271)	(724)
Contributions from noncontrolling interests in other partnerships			2,469	1,828
Acquisition of subsidiary interest from noncontrolling interest			(25,791)	0
Dividends / Distributions paid on common and preferred stock / units			(161,813)	(168,411)
Other obligations related to loan participations			0	(3)
Tax withholdings related to restricted share awards			(3,126)	(3,842)
Deferred loan costs and capitalized lease obligation			(14,624)	(1,536)
Net cash provided by (used in) financing activities			210,523	(384,322)
Net (decrease) increase in cash, cash equivalents, and restricted cash			(37,966)	129,954
Cash, cash equivalents, and restricted cash at beginning of year			279,113	250,026	250,026
Cash, cash equivalents, and restricted cash at end of period	241,147	379,980	241,147	379,980	279,113
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Issuance of units in the Operating Partnership			0	15,448
Conversion of units in the Operating Partnership for common stock			446	1,560
Derivative instruments at fair value			0	6,937
Tenant improvements and capital expenditures payable			9,021	16,534
Fair value adjustment to noncontrolling interest in Operating Partnership			43,835	4,493
Deconsolidation of subsidiaries			0	298,403
Transfer of assets related to assets held for sale			0	593,995
Transfer of liabilities related to assets held for sale			0	265,538
Removal of fully depreciated commercial real estate properties			5,728	110,594
Contribution to consolidated joint venture by noncontrolling interest			48,223	0
Share repurchase payable			0	31,605
Recognition of right of use assets and related lease liabilities			389,120	0
Cash and cash equivalents						148,978	129,475	287,240
Restricted cash						92,169	149,638	92,740
Total cash, cash equivalents, and restricted cash	$ 241,147	$ 379,980	$ 279,113	$ 250,026	$ 279,113	$ 241,147	$ 279,113	$ 379,980