Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract] Deferred Costs Deferred Financing and Leasing Costs Disclosure [Text Block] Costs incurred in connection with financing activities (fees to banks) and costs incurred in connection with leasing activities (fees to real estate brokers), net of amortization. Equity Method Investments and Joint Ventures [Abstract] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Real Estate Properties, Type of Property [Axis] Real Estate Properties, Type of Property [Axis] Represents details pertaining to the types of real estate properties. Real Estate Properties, Type of Property [Domain] Real Estate Properties, Type of Property [Domain] Identifies real estate properties by type. Three Residential Units Three Residential Units [Member] Three Residential Units [Member] Three Retail and Two Residential Units Three Retail and Two Residential Units [Member] Three Retail and Two Residential Units [Member] Real Estate by Location [Axis] Real Estate by Location [Axis] Represents details pertaining to the locations of real estate properties of the entity. Real Estate by Location [Domain] Real Estate by Location [Domain] Identifies real estate properties of the entity by location. 21 East 66th Street East 21 Street 66 [Member] Represents the information pertaining to 21 East 66th Street, a joint venture property of the entity. Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Group Name [Domain] Disposal Group Name [Domain] East 400 Street 57 [Member] East 400 Street 57 [Member] Represents information pertaining to 400 East 57th Street, a property owned by the entity. 11 Madison Avenue 11 Madison Ave [Member] 11 Madison Ave [Member] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Partners' Interest General Partner [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] 100 Park Avenue Park Avenue, 100 [Member] Represents the information pertaining to 100 Park Avenue, a joint venture property of the entity. 717 Fifth Avenue Fifth Avenue, 717 [Member] Represents the information pertaining to 717 Fifth Avenue, a joint venture property of the entity. 800 Third Avenue Third Avenue, 800 [Member] Represents the information pertaining to 800 Third Avenue, a joint venture property of the entity. 1745 Broadway Broadway, 1745 [Member] Represents the information pertaining to 1745 Broadway, a joint venture property of the entity. Jericho Plaza Jericho Plaza 1 and 2 [Member] Represents the information pertaining to 1 and 2 Jericho Plaza, a joint venture property of the entity. 11 West 34th Street West 11 Street 34 [Member] Represents the information pertaining to 11 West 34th Street, a joint venture property of the entity. 3 Columbus Circle Columbus Circle, 3 [Member] Represents the information pertaining to 3 Columbus Circle, a joint venture property of the entity. 280 Park Avenue Park Avenue, 280 [Member] Represents the information pertaining to 280 Park Avenue, a joint venture property of the entity. 1552-1560 Broadway Broadway 1552 to 1560 [Member] Represents the information pertaining to 1552-1560 Broadway, a joint venture property of the entity. 724 Fifth Avenue Fifth Avenue 724 [Member] Represents the information pertaining to 724 Fifth Avenue, a property acquired by the entity under the joint venture. 10 East 53rd Street East 53rd Street 10 [Member] Represents information pertaining to 10 East 53rd Street, a joint venture property of the entity. 521 Fifth Avenue Fifth Avenue, 521 [Member] Represents the information pertaining to 521 Fifth Avenue, a property owned by the entity. 650 Fifth Avenue 650 Fifth Avenue [Member] 650 Fifth Avenue [Member] 121 Greene Street Greene Street 121 [Member] Greene Street 121 [Member] 175-225 Third Street Brooklyn, New York Third Street 175-225 [Member] Third Street 175-225 [Member] 55 West 46th Street West 46th Street 55 [Member] West 46th Street 55 [Member] Stonehenge Portfolio Stonehenge Properties [Member] Represents the information pertaining to Stonehenge Properties. 131-137 Spring Street Spring Street 131 to 137 [Member] Represents information pertaining to property located at 131-137 Spring Street, owned by the entity. 76 11th Avenue 76 11th Avenue [Member] 76 11th Avenue [Member] 605 West 42nd Street 605 West 42nd Street [Member] 605 West 42nd Street [Member] 1552 Broadway Broadway 1552 [Member] Represents information pertaining to 1552 Broadway, a joint venture property of the entity. 333 East 22nd St 333 East 22nd St [Member] 333 East 22nd St [Member] Real Estate, Type of Property [Axis] Real Estate, Type of Property [Axis] Real Estate, Property Type [Domain] Real Estate [Domain] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Joint venture Corporate Joint Venture [Member] General information on each joint venture Schedule of Equity Method Investments [Line Items] Net equity investment in VIEs in which the entity is not primary beneficiary Variable Interest Entity Not Primary Beneficiary, Investment Represents the amount of equity investment in variable interest entities (VIEs) in which the entity is not a primary beneficiary. Ownership Interest (as a percent) Equity Method Investment, Ownership Percentage Economic Interest (as a percent) Equity Method Investment, Economic Interest Percentage The percentage of economic interest in the investee accounted for under the equity method of accounting. Approximate Square Feet (sqft) Area of Real Estate Property Acquisition Price Equity Method Investment, Aggregate Cost Number of Stores Number of Stores Number Of Residential Units Number Of Residential Units Number Of Residential Units Number of mezzanine notes secured by interests in the entity which owns 76 11th avenue Number of Mezzanine Notes Secured Number of Mezzanine Notes Secured Exit fee, percentage owned Exit Fee, Percentage Owned Exit Fee, Percentage Owned Extension Fee, Percentage Owned Extension Fee, Percentage Owned Extension Fee, Percentage Owned Mezzanine loan Loans and Leases Receivable, Gross Ownership percentage in disposed asset Disposal Group Including Discontinued Operation, Ownership Percentage in Disposed Asset Disposal Group Including Discontinued Operation, Ownership Percentage in Disposed Asset Equity method investments, depreciation Equity Method Investments, Depreciation Equity Method Investments, Depreciation Equity method investment, assets Equity Method Investment, Summarized Financial Information, Assets Segment Reporting [Abstract] Schedule of selected results of operations and selected asset information Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of reconciliation of income from continuing operations to net income attributable to SL Green common stockholders Schedule of Income (Loss) Available to Common Stockholders [Table Text Block] Tabular disclosure of the information pertaining to income (loss) attributable to common stockholders of the entity. This item may include reconciliation of income (loss) from continuing operations to net income (loss) attributable to common stockholders. Stockholders' Equity Note [Abstract] Stockholders' Equity of the Company Stockholders' Equity Note Disclosure [Text Block] Equity [Abstract] Stockholders Equity [Table] Stockholders Equity [Table] Disclosure of information pertaining to changes in stockholders' equity during the period. SL Green Operating Partnership Subsidiaries [Member] Stockholders' Equity Stockholders Equity [Line Items] -- None. No documentation exists for this element. -- Partners' Capital of the Operating Partnership Debt Disclosure [Abstract] Schedule of senior unsecured notes and other related disclosures by scheduled maturity date Schedule of Long-term Debt Instruments [Table Text Block] Schedule of combined aggregate principal maturities Schedule of Maturities of Long-term Debt [Table Text Block] Schedule of consolidated interest expense, excluding capitalized interest Schedule of Interest Expense [Table Text Block] Tabular disclosure of the information pertaining to interest expenses incurred during the period but excluding the interest capitalized. The disclosure may include interest income earned during the period. Document and Entity Information -- None. No documentation exists for this element. -- Document Information [Table] Document Information [Table] Document Information [Line Items] Document Information [Line Items] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus (Q1,Q2,Q3,FY) Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Business Segments [Axis] Segments [Axis] Segment [Domain] Segments [Domain] Real Estate Segment Real Estate Segment [Member] Represents the information pertaining to the reportable segment of the entity, Real Estate Segment. Debt and Preferred Equity Segment Structured Finance Segment [Member] Represents the information pertaining to the reportable segment of the entity, Structured Finance Segment. Segment information Segment Reporting Information [Line Items] Number of reportable segments (segment) Number of Reportable Segments Total revenues Revenues Net income before equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities Income (Loss) from Continuing Operations before Realized Gain (Loss) on Disposal of Equity Method Investment This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before realized gains (losses) on disposals of equity method investments, extraordinary items, and noncontrolling interest. Total assets Assets Marketing, general and administrative Selling, General and Administrative Expense Investments, Debt and Equity Securities [Abstract] Mortgage Loans on Real Estate Schedule [Table] Mortgage Loans on Real Estate Schedule [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Total fixed rate Fixed Rate [Member] Fixed Rate [Member] Total floating rate Debt Investment with Floating Interest Rate [Member] Represents the debt investment in mortgage loans having a floating interest rate. Mortgage Loans on Real Estate, Loan Type [Axis] Mortgage Loans on Real Estate, Loan Type [Axis] Mortgage Loans on Real Estate, Loan Type [Domain] Mortgage Loans on Real Estate, Loan Type [Domain] Junior Mortgage Participation Acquired in September 2014 [Member] Junior Mortgage Participation Acquired in September 2014 [Member] Junior Mortgage Participation Acquired in September 2014 [Member] Junior Mortgage Participation/Mezzanine Loan, March 2017 Junior Mortgage Participation or Mezzanine Loan repaid in March 2017 [Member] Junior Mortgage Participation or Mezzanine Loan repaid in March 2017 [Member] Mezzanine Loan, June 2017 Mezzanine Loan, with an Initial Maturity Date of June 2017 [Member] Mezzanine Loan, with an Initial Maturity Date of June 2017 [Member] Mortgage/Mezzanine Loan, with an Initial Maturity Date of August 2018 [Member] Mortgage/Mezzanine Loan, with an Initial Maturity Date of August 2018 [Member] Mortgage/Mezzanine Loan, with an Initial Maturity Date of August 2018 [Member] Mortgage Loan with an Initial Maturity Date of August 2018 [Member] Mortgage Loan with an Initial Maturity Date of August 2018 [Member] Mortgage Loan with an Initial Maturity Date of August 2018 [Member] Mezzanine Loan with an Initial Maturity Date of August 2018 [Member] Mezzanine Loan with an Initial Maturity Date of August 2018 [Member] Mezzanine Loan with an Initial Maturity Date of August 2018 [Member] Mezzanine Loan with an Initial Maturity Date of September 2018 [Member] Mezzanine Loan with an Initial Maturity Date of September 2018 [Member] Mezzanine Loan with an Initial Maturity Date of September 2018 [Member] Mezzanine Loan with an Initial Maturity Date of October 2018 [Member] Mezzanine Loan with an Initial Maturity Date of October 2018 [Member] Mezzanine Loan with an Initial Maturity Date of October 2018 [Member] Mezzanine Loan with an Initial Maturity Date of November 2018 [Member] Mezzanine Loan with an Initial Maturity Date of November 2018 [Member] Mezzanine Loan with an Initial Maturity Date of November 2018 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018, 2 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018, 2 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018, 2 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018, 3 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018, 3 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018, 3 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018, 4 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018, 4 [Member] Mezzanine Loan with an Initial Maturity Date of December 2018, 4 [Member] Mezzanine Loan with an Initial Maturity Date of January 2019 [Member] Mezzanine Loan with an Initial Maturity Date of January 2019 [Member] Mezzanine Loan with an Initial Maturity Date of January 2019 [Member] Mezzanine Loan with an Initial Maturity Date of January 2019, 2 [Member] Mezzanine Loan with an Initial Maturity Date of January 2019, 2 [Member] Mezzanine Loan with an Initial Maturity Date of January 2019, 2 [Member] Mezzanine Loan with an Initial Maturity of January 2019, 3 [Member] Mezzanine Loan with an Initial Maturity of January 2019, 3 [Member] Mezzanine Loan with an Initial Maturity of January 2019, 3 [Member] Mezzanine Loan with an Initial Maturity of March 2019 [Member] Mezzanine Loan with an Initial Maturity of March 2019 [Member] Mezzanine Loan with an Initial Maturity of March 2019 [Member] Mezzanine Loan with an Initial Maturity Date of April 2019 [Member] Mezzanine Loan with an Initial Maturity Date of April 2019 [Member] Mezzanine Loan with an Initial Maturity Date of April 2019 [Member] Mortgage/Jr Mortgage Participate Loan, Maturity Date of August 2019 [Member] Mortgage/Jr Mortgage Participate Loan, Maturity Date of August 2019 [Member] Mortgage/Jr Mortgage Participate Loan, Maturity Date of August 2019 [Member] Mezzanine Loan, Maturity of September 2019 [Member] Mezzanine Loan, Maturity of September 2019 [Member] Mezzanine Loan, Maturity of September 2019 [Member] Mortgage/Mezzanine Loan with an Initial Maturity of September 2019 [Member] Mortgage/Mezzanine Loan with an Initial Maturity of September 2019 [Member] Mortgage/Mezzanine Loan with an Initial Maturity of September 2019 [Member] Mortgage/Mezzanine Loan with an Initial Maturity of January 2020 [Member] [Member] Mortgage/Mezzanine Loan with an Initial Maturity of January 2020 [Member] [Member] Mortgage/Mezzanine Loan with an Initial Maturity of January 2020 [Member] [Member] Mezzanine Loan with an Initial Maturity of January 2020 [Member] Mezzanine Loan with an Initial Maturity of January 2020 [Member] Mezzanine Loan with an Initial Maturity of January 2020 [Member] Jr Mortgage Participation/Mezzanine Loan with an Initial Maturity of July 2021 [Member] Jr Mortgage Participation/Mezzanine Loan with an Initial Maturity of July 2021 [Member] Jr Mortgage Participation/Mezzanine Loan with an Initial Maturity of July 2021 [Member] Mezzanine Loan Repaid in December 2016 [Member] Mortgage/Mezzanine Loan repaid in January 2017 [Member] Mortgage/Mezzanine Loan repaid in January 2017 [Member] Mortgage Loan, February 2019 Mortgage Loan With An Initial Maturity Date Of February 2019 [Member] Mortgage Loan With An Initial Maturity Date Of February 2019 [Member] Mortgage Loan, August 2019 Mortgage Loan with an Initial Maturity of August 2019 [Member] Mortgage Loan with an Initial Maturity of August 2019 [Member] Mezzanine Loan with an Initial Maturity Date of March 2020 [Member] Mezzanine Loan with an Initial Maturity Date of March 2020 [Member] Mezzanine Loan with an Initial Maturity Date of March 2020 [Member] Mezzanine Loan, September 2021 Mezzanine Loan with an Initial Maturity Date of September 2021 [Member] Mezzanine Loan with an Initial Maturity Date of September 2021 [Member] Mezzanine Loan, November 2023 Mezzanine Loan, with an Initial Maturity Date of November 2023 [Member] Mezzanine Loan, with an Initial Maturity Date of November 2023 [Member] Mezzanine Loan, June 2024 Mezzanine Loan with an Initial Maturity Date of June 2024 [Member] Mezzanine Loan with an Initial Maturity Date of June 2024 [Member] Mezzanine Loan, January 2025 Mezzanine Loan, with an Initial Maturity Date of January 2025 [Member] Mezzanine Loan, with an Initial Maturity Date of January 2025 [Member] Mezzanine Loan with an Initial Maturity Date of November 2026 [Member] Mezzanine Loan with an Initial Maturity Date of November 2026 [Member] Mezzanine Loan with an Initial Maturity Date of November 2026 Mortgage/Mezzanine Loan, June 2017 Mezzanine Loan with an Initial Maturity Date of June 2017, 2 [Member] Mezzanine Loan with an Initial Maturity Date of June 2017, 2 [Member] Mortgage/Mezzanine Loan with an Initial Maturity Date of July 2017 [Member] Mortgage/Mezzanine Loan with an Initial Maturity Date of July 2017 [Member] Mortgage/Mezzanine Loan with an Initial Maturity Date of July 2017 [Member] Mortgage/Mezzanine Loan, September 2017 [Member] Mortgage/Mezzanine Loan, September 2017 [Member] Mortgage/Mezzanine Loan, September 2017 [Member] Mortgage/Mezzanine Loan with an Initial Maturity Date of October 2017 [Member] Mortgage/Mezzanine Loan with an Initial Maturity Date of October 2017 [Member] Mortgage/Mezzanine Loan with an Initial Maturity Date of October 2017 [Member] Mezzanine Loan with an Initial Maturity Date of November 2017 [Member] Mezzanine Loan with an Initial Maturity Date of November 2017 [Member] Mezzanine Loan with an Initial Maturity Date of November 2017 [Member] Mezzanine Loan with an Initial Maturity Date of December 2017 [Member] Mezzanine Loan with an Initial Maturity Date of December 2017 [Member] Mezzanine Loan with an Initial Maturity Date of December 2017 [Member] Mezzanine Loan with an Initial Maturity Date of December 2017, 2 [Member] Mezzanine Loan with an Initial Maturity Date of December 2017, 2 [Member] Mezzanine Loan with an Initial Maturity Date of December 2017, 2 [Member] Mortgage Mezzanine Loan with an Initial Maturity Date of December 2017 [Member] Mortgage Mezzanine Loan with an Initial Maturity Date of December 2017 [Member] Mortgage Mezzanine Loan with an Initial Maturity Date of December 2017 [Member] Junior Mortgage Participation Loan with an Initial Maturity Date of April 2018 [Member] Mortgage/Mezzanine Loan with an Initial Maturity Date of January 2018 [Member] Mortgage/Mezzanine Loan with an Initial Maturity Date of January 2018 [Member] Mezzanine Loan with an Initial Maturity Date of April 2018 [Member] Mezzanine Loan with an Initial Maturity Date of April 2018 [Member] Mezzanine Loan with an Initial Maturity Date of April 2018 [Member] Junior Mortgage Participation Loan with an Initial Maturity Date of April 2018 [Member] Junior Mortgage Participation Loan with an Initial Maturity Date of April 2018 [Member] Junior Mortgage Participation Loan with an Initial Maturity Date of April 2018 [Member] Junior Mortgage Participation, Related To Mortgage Loan, February 2019 Junior Mortgage Participation, Related To Mortgage Loan, February 2019 [Member] Junior Mortgage Participation, Related To Mortgage Loan, February 2019 [Member] Debt Investments in Mortgage Loans [Member] Debt Investments in Mortgage Loans [Member] Represents debt investments in mortgage loans on real estate. Debt investment Mortgage Loans on Real Estate [Line Items] Increase in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale Mortgage Loans on Real Estate Period Increase Represents the increase to mortgage loans on real estate during the period, due to originations, purchases, accretion of discounts and paid-in-kind interest. Decrease in debt and preferred equity investments (net of discounts), including investments classified as held-for-sale Mortgage Loans on Real Estate Period Decrease Represents the decrease to mortgage loans on real estate during the period, due to repayments, participations, sales, foreclosures and loan loss reserves. Aggregate weighted average current yield (as a percent) Mortgage Loans on Real Estate, Interest Rate Debt Investments Held [Abstract] Debt Investments Held [Abstract] Debt Investments Held [Abstract] Future Funding Obligations Loans and Leases Receivable, Funding Obligation Loans and Leases Receivable, Funding Obligation Senior Financing Mortgage Loans on Real Estate, Senior Debt on Investment Amount as of the balance sheet date of debt which holds a position senior to the entity's investment in a mortgage loan on real estate. Carrying Value, Net of Discounts and Deferred Origination Fees Carrying Value, Net of Discounts and Deferred Origination Fees Mortgage Loans on Real Estate, Commercial and Consumer, Net Amount participated out Mortgage Loans on Real Estate Loan Value Represents the amount of loan participation on property mortgage. Loan acquired Receivable with Imputed Interest, Face Amount Discount amount Receivable with Imputed Interest, Discount Purchase option, percentage of underlying asset Investments in Unconsolidated Joint Ventures Equity Method Investments and Joint Ventures Disclosure [Text Block] Business Combinations [Abstract] Property Acquisitions Business Combination Disclosure [Text Block] Accounting Policies [Abstract] Schedule of Property, Plant and Equipment and Finite Lived Intangible Assets and Liabilities, by Major Class [Table] Schedule of Property, Plant and Equipment and Finite Lived Intangible Assets and Liabilities, by Major Class [Table] Table of long-lived, physical assets and finite lived intangible assets and liabilities that are used in the normal conduct of business to produce goods and services and which are not intended for resale. Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Building Building [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Above-market leases Above Market Leases [Member] Below-market leases Leases, Below Market [Member] Leases, Below Market [Member] In-place leases In Place Leases [Member] Represents information pertaining to in-place leases. Investment in Commercial Real Estate Properties Property, Plant and Equipment [Line Items] Estimated useful life (in years) Property, Plant and Equipment, Useful Life Estimated useful life of other intangible assets (in years) Finite-Lived Intangible Asset, Useful Life Rental revenue from amortization of acquired leases Rental Revenue Increase (Decrease) Acquired Lease Amortization Represents the increase (decrease) in rental revenue during the period resulting from the net amortization of acquired above-market and below-market leases. Reduction in interest expense from amortization of above-market rate mortgages Interest Expense Increase (Decrease) Assumed Above Market Rate Mortgage Amortization Represents the increase (decrease) in interest expense during the period resulting from the amortization of assumed above-market rate mortgages. Identified intangible assets (included in other assets): Finitely Lived Intangible Assets [Abstract] -- None. No documentation exists for this element. -- Gross amount Finite-Lived Intangible Assets, Gross Accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Net Finite-Lived Intangible Assets, Net Identified intangible liabilities (included in deferred revenue): Finite Lived Intangible Liabilities [Abstract] -- None. No documentation exists for this element. -- Gross amount Finite Lived Intangible Liabilities, Gross Represents the gross carrying amounts before accumulated amortization as of the balance sheet date of all intangible liabilities having statutory or estimated useful lives. Accumulated amortization Finite Lived Intangible Liabilities, Accumulated Amortization Represents the accumulated amount of amortization of a major finite-lived intangible liability class. Net Finite Lived Intangible Liabilities, Net Represents the sum of gross carrying value of a major finite-lived intangible liability class, less accumulated amortization. Net intangible assets reclassed to assets held for sale Net Intangible Assets Transferred to Assets Held for Sale Net Intangible Assets Transferred to Assets Held for Sale Net intangible liabilities reclassed to liabilities relates to assets held for sale Net Intangible Liabilities Transferred to Liabilities Related to Assets Held for Sale Net Intangible Liabilities Transferred to Liabilities Related to Assets Held for Sale Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Revolving credit facility Revolving Credit Facility [Member] Term loan Term Loan [Member] Represents the term loan of the reporting entity. 2012 Credit Facility Credit Facility 2012 [Member] Represents information pertaining to 2012 Credit Facility. Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] LIBOR London Interbank Offered Rate (LIBOR) [Member] Line of Credit Line of Credit [Member] Corporate Indebtedness Debt Instrument [Line Items] Credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Maximum borrowing capacity, optional expansion Line of Credit Facility, Optional Expansion, Maximum Borrowing Capacity The expanded maximum borrowing capacity available, which is subject to agreement with the entity. Interest rate added to base rate (as a percent) Debt Instrument, Basis Spread on Variable Rate Effective rate (as a percent) Debt Instrument, Interest Rate, Effective Percentage Facility fee (as a percent) Line of Credit Facility, Commitment Fee Percentage Letters of credit Letters of Credit Outstanding, Amount Outstanding under line of credit facility Long-term Line of Credit Ability to borrow under line of credit facility Line of Credit Facility, Remaining Borrowing Capacity Long-term debt, carrying value Long-term Debt Summary of debt investments Schedule of Mortgage Loans on Real Estate [Table Text Block] Tabular disclosure of investments in mortgage loans on real estate. Summary of preferred equity investments Investments Classified by Contractual Maturity Date [Table Text Block] Income taxes Income Tax Disclosure [Abstract] Federal, state and local tax provision Income Tax Expense (Benefit) Net income attributable to SLGOP common unitholders Net Income (Loss) Allocated to, Common Unitholders This element represents amounts attributable to ROP common unitholders. Weighted average common shares outstanding (shares) Weighted Average Number of Shares Outstanding, Basic Stock-based compensation plans (shares) Incremental Common Units Attributable to Share based Payment Arrangements Incremental Common Units Attributable to Share based Payment Arrangements Diluted weighted average common units outstanding (shares) Weighted Average Number of Units Outstanding Diluted Weighted Average Number of Units Outstanding Diluted Common stock shares excluded from the diluted shares outstanding (shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Organization, Consolidation and Presentation of Financial Statements [Abstract] Schedule of Ownership Interests [Table] Schedule of Ownership Interests [Table] Represents information related to ownership interests held by the entity. Variable Interest Entities [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Service Corporation Variable Interest Entity, Primary Beneficiary [Member] Organization Ownership Interests [Line Items] -- None. No documentation exists for this element. -- Percentage of ownership in SL Green Management LLC owned by operating partnership (percent) Subsidiary of Limited Liability Company or Limited Partnership, Ownership Interest Noncontrolling interest in the operating partnership (as a percent) Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Statement of Stockholders' Equity [Abstract] Cash distribution declared, per common share (in dollars per share) Common Stock, Dividends, Per Share, Declared Weighted Average Weighted Average [Member] 21 East 66th Street 280 Park Avenue Jericho Plaza Jericho Plaza [Member] Jericho Plaza [Member] 11 West 34th Street Initial Maturity July 2022 Secured Debt, Initial Maturity July 2022 [Member] Secured Debt, Initial Maturity July 2022 [Member] Initial Maturity July 2022, 2 Secured Debt, Initial Maturity July 2022, 2 [Member] Secured Debt, Initial Maturity July 2022, 2 [Member] Initial Maturity November 2017 Secured Debt, Initial Maturity November 2017 [Member] Secured Debt, Initial Maturity November 2017 [Member] Initial Maturity August 2019 Secured Debt, Initial Maturity August 2019 [Member] Secured Debt, Initial Maturity August 2019 [Member] Initial Maturity June 2024 Secured Debt, Initial Maturity June 2024 [Member] Secured Debt, Initial Maturity June 2024 [Member] Initial Maturity June 2017 Floating-Rate Mortgage Maturing in June 2017 [Member] Floating-Rate Mortgage Maturing in June 2017 [Member] Initial Maturity December 2017 Floating-Rate Mortgage Maturing in December 2017 [Member] Floating-Rate Mortgage Maturing in December 2017 [Member] Mortgage loan Mortgages [Member] Mezzanine loans Mezzanine Loans on Real Estate [Member] Represents the mezzanine loans on real estate properties. Interest rate, fixed rate debt (as a percent) Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate Interest rate, floating rate debt (as a percent) Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate Total fixed rate debt Secured Debt, Bearing Fixed Interest, Amount The portion of the carrying amount of long-term secured loans outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate. Total floating rate debt Secured Debt, Bearing Variable Interest, Amount The portion of the carrying amount of long-term secured loans outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time. Total fixed rate and floating rate debt Secured Debt and Other Loans, Payable Represents the carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations and other loans payable. Deferred financing costs, net Debt Issuance Costs, Net Total joint venture mortgages and other loans payable, net Secured Debt and Other Loans, Payable, Net Secured Debt and Other Loans, Payable, Net Committed amount Debt Instrument, Committed Amount Represents the maximum committed amount of the debt instrument. Unfunded amount Debt Instrument, Unfunded Amount Debt Instrument, Unfunded Amount Ownership Percentage Term (in Years) Debt Instrument, Term Face amount of loan Debt Instrument, Face Amount Significant Accounting Policies Significant Accounting Policies [Text Block] Noncontrolling Interest [Abstract] Schedule of Preferred Units [Table] Schedule of Preferred Units [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Preferred Units Preferred Stock [Member] Preferred Units [Line Items] Preferred Units [Line Items] Noncontrolling interest in the operating partnership (as a percent) Rollforward Analysis of Preferred Unit Activity Rollforward Analysis of Preferred Unit Activity [Roll Forward] Rollforward Analysis of Preferred Unit Activity [Roll Forward] Balance at beginning of period Noncontrolling Interest in Preferred Unit Holders Issuance of preferred units Noncontrolling Interest, Increase from Subsidiary Equity Issuance Redemption of preferred units Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Balance at end of period Number of units of operating partnership owned by the noncontrolling interest unit holders (units) Minority Interest Units of Partnership Owned by Noncontrolling Owners Represents the number of partnership units owned by the noncontrolling unit holders. Interest expense Interest Income (Expense), Net [Abstract] Interest expense before capitalized interest Interest Expense Interest capitalized Capitalized Interest Costs, Including Allowance for Funds Used During Construction Interest income Interest Income, Operating Interest expense, net Interest Income (Expense), Net Derivative Instruments and Hedging Activities Disclosure [Abstract] Schedule of notional and fair value of derivative financial instruments and foreign currency hedges Schedule of Derivative Instruments [Table Text Block] Schedule of effect of derivative financial instruments on consolidated statements of income Derivative Instruments, Gain (Loss) [Table Text Block] Summary of identified intangible assets (acquired above-market leases and in-place leases) and intangible liabilities (acquired below-market leases) Schedule of Intangible Assets and Liabilities [Table Text Block] Tabular disclosure of the aggregate amount of intangible assets and liabilities. Schedule of marketable securities Available-for-sale Securities [Table Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Schedule of weighted average assumptions used to estimate the grant date fair value of options granted Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Summary of the status of stock options and changes during the period Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block] Summary of restricted stock and charges during the period Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Statement [Table] Statement [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Preferred Stock Common Stock Common Stock [Member] Additional Paid- In-Capital Additional Paid-in Capital [Member] Treasury Stock Treasury Stock [Member] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Retained Earnings Retained Earnings [Member] Noncontrolling Interests Noncontrolling Interest [Member] Statement Statement [Line Items] Increase (Decrease) in Stockholders' Equity Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning Balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Beginning Balance (in shares) Shares, Outstanding Net income (loss) Profit (Loss) Less Minority Interest in Net Income (Loss) Operating Partnerships Net income including minority interest in partnerships. Other comprehensive loss Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Preferred dividends Dividends, Preferred Stock DRSPP proceeds (in shares) Stock Issued During Period, Shares, Dividend Reinvestment Plan DRSPP proceeds Stock Issued During Period, Value, Dividend Reinvestment Plan Conversion of units of the Operating Partnership to common stock (in shares) Stock Issued During Period, Shares, Conversion of Units Conversion of units of the Operating Partnership to common stock Stock Issued During Period, Value, Conversion of Units Reallocation of noncontrolling interest in the Operating Partnership Reallocation of Noncontrolling Interest to (from) Operating Partnership Reallocation of Noncontrolling Interest to (from) Operating Partnership Deferred compensation plan and stock award, net (in shares) Deferred Compensation Plan and Stock Award, Shares Number of shares issued during the period from a Deferred Compensation Plan and Stock Award. Deferred compensation plan and stock award, net Deferred Compensation Plan and Stock Award, Net Value of stock issued during the period from a deferred compensation plan and stock award, net. Amortization of deferred compensation plan Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Proceeds from stock options exercised (in shares) Common Stock Issued During Period, Shares New Issues This element represents the number of new common stock issued during the period. Proceeds from stock options exercised Common Stock Issued During Period, Value New Issues This element represents the value of new common stock issued during the period. Contributions to consolidated joint venture interests Consolidation of Joint Venture Interest This element represent the net income (loss) in consolidation of joint venture interest. Cash distributions to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Cash distributions declared ($0.775 per common share, none of which represented a return of capital for federal income tax purposes) Dividends, Common Stock Ending Balance Ending Balance (in shares) Mezzanine loan due July 2036 Mezzanine Loan Due July 2036 [Member] Mezzanine Loan Due July 2036 [Member] Mezzanine loan due February 2022 Participating Financing Due February 2022 [Member] Participating Financing Due February 2022 [Member] Participating Financing Due March 2018 [Member] Participating Financing Due March 2018 [Member] Participating Financing Due March 2018 [Member] Schedule of Equity Method Investments [Line Items] Acquisition, development and construction arrangements, carrying value Loans Receivable, Gross, Commercial, Acquisition Segment Information Segment Reporting Disclosure [Text Block] Discontinued Operations and Disposal Groups [Abstract] Properties Held for Sale and Property Dispositions Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Fair Value, by Balance Sheet Grouping Fair Value, by Balance Sheet Grouping [Table Text Block] Statement of Partners' Capital [Abstract] Partner Capital Components [Axis] Partner Capital Components [Axis] Partner Capital Components [Domain] Partner Capital Components [Domain] Increase (Decrease) in Partner's Capital Beginning Balance Partners' Capital, Including Portion Attributable to Noncontrolling Interest Beginning Balance (units) Partners' Capital Account, Units Net income (loss) Profit Loss, Less Preferred Distributions The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest, less preferred distributions during the period. Other comprehensive loss Other Comprehensive Income (Loss), Net of Tax, Less Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss), Net of Tax, Less Portion Attributable to Noncontrolling Interest Preferred distributions Distributions Preferred Units Distributions declared for preferred units during the period. DRSPP proceeds Conversion of common units (in shares) Partners' Capital Account, Units, Sale of Units Conversion of common units Reallocation of noncontrolling interests in the operating partnership Deferred compensation plan and stock award, net Contribution to consolidated joint venture interests Contributions - proceeds from stock options exercised (in shares) Contributions - proceeds from stock options exercised Partners' Capital Account, Option Exercise Cash distributions declared ($0.775 per common unit, none of which represented a return of capital for federal income tax purposes) Partners' Capital Account, Distributions Ending Balance Ending Balance (units) Organization and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Statement of Comprehensive Income [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Other comprehensive loss: Other Comprehensive Income (Loss), Net of Tax [Abstract] Change in net unrealized gain (loss) on derivative instruments, including SL Green's/SLGOP's share of joint venture net unrealized (loss) gain on derivative instruments Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Change in unrealized gain on marketable securities Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Other comprehensive loss Other Comprehensive Income (Loss), Net of Tax Comprehensive (loss) income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Net loss (income) attributable to noncontrolling interests and preferred units distributions Net Income (Loss) Attributable to Noncontrolling Interest Net loss (income) attributable to noncontrolling interests Noncontrolling Interest in Net Income (Loss) Other Noncontrolling Interests, Redeemable Other comprehensive loss attributable to noncontrolling interests Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest Comprehensive income attributable to SL Green/SLGOP Comprehensive Income (Loss), Net of Tax, Attributable to Parent Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] Equity marketable securities Equity Securities [Member] Commercial mortgage-backed securities Commercial Mortgage Backed Securities [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying Value Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Accrued Interest Payable And Other Liabilities Accrued Interest Payable And Other [Member] Accrued Interest Payable And Other [Member] Fair Value of Financial Instruments Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Marketable securities Available-for-sale Securities Interest rate cap and swap agreements (included in other assets) Derivative Asset, Fair Value, Gross Asset Interest rate cap and swap agreements Derivative Liability, Fair Value, Gross Liability Debt and preferred equity investments Fixed rate debt Long-term Debt, Percentage Bearing Fixed Interest, Amount Variable rate debt Long-term Debt, Percentage Bearing Variable Interest, Amount Total Long-term Debt, Fair Value Estimated fair value of debt and preferred equity investments, low end of range Mortgage Loans on Real Estate, Fair Value, Low End of Range Represents the low end of the range of estimated fair value for investments in mortgage loans on real estate. Estimated fair value of debt and preferred equity investments, high end of range Mortgage Loans on Real Estate Fair Value, High End of Range Represents the high end of the range of estimated fair value for investments in mortgage loans on real estate. Trust Preferred Securities Junior Subordinated Debt [Member] Mortgages and other loans payable Mortgage and Other Loans Payable [Member] Represents mortgage and other loans payable of the entity. Revolving Credit Facility Unsecured Term Loan Senior Unsecured Notes Senior Notes [Member] Joint Venture Debt Debt Instrument [Line Items] Proceeds from Issuance of Debt Proceeds from Issuance of Debt Scheduled Amortization Future Amortization of Debt [Abstract] -- None. No documentation exists for this element. -- Remaining 2017 Future Amortization of Debt, First Full Fiscal Year The amount of amortization of debt expected to be recognized during the first full fiscal year following the date of the most recent balance sheet. 2017 Future Amortization of Debt, Second Full Fiscal Year The amount of amortization of debt expected to be recognized during the second full fiscal year following the date of the most recent balance sheet. 2018 Future Amortization of Debt, Third Full Fiscal Year The amount of amortization of debt expected to be recognized during the third full fiscal year following the date of the most recent balance sheet. 2019 Future Amortization of Debt Fourth Full Fiscal Year The amount of amortization of debt expected to be recognized during the fourth full fiscal year following the date of the most recent balance sheet. 2020 Future Amortization of Debt Fifth Full Fiscal Year The amount of amortization of debt expected to be recognized during the fifth full fiscal year following the date of the most recent balance sheet. Thereafter Future Amortization of Debt after Fifth Full Fiscal Year The amount of amortization of debt expected to be recognized after the fifth full fiscal year following the date of the most recent balance sheet. Total amortization of debt Future Amortization of Debt The total expected future amortization of debt. Principal Repayments and Joint Venture Debt Maturities of Long-term Debt [Abstract] Remaining 2017 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 2017 Long-term Debt, Maturities, Repayments of Principal in Year Two 2018 Long-term Debt, Maturities, Repayments of Principal in Year Three 2019 Long-term Debt, Maturities, Repayments of Principal in Year Four 2020 Long-term Debt, Maturities, Repayments of Principal in Year Five Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Total principal repayments Long Term Debt, Maturities, Repayments of Principal Total amount of long-term debt maturing in future periods. Scheduled Amortization and Principal Repayments Amortization and Maturities of Long-term Debt [Abstract] -- None. No documentation exists for this element. -- Remaining 2017 Future Amortization of Debt and Long Term Debt, Maturities, Repayments of Principal First Full Fiscal Year The aggregate amount of amortization of debt expected to be recognized and long-term debt maturing within the first full fiscal year following the date of the latest balance sheet presented in the financial statements. 2017 Future Amortization of Debt and Long Term Debt, Maturities, Repayments of Principal Second Full Fiscal Year The aggregate amount of amortization of debt expected to be recognized and long-term debt maturing within the second full fiscal year following the date of the latest balance sheet presented in the financial statements. 2018 Future Amortization of Debt and Long Term Debt, Maturities, Repayments of Principal Third Full Fiscal Year The aggregate amount of amortization of debt expected to be recognized and long-term debt maturing within the third full fiscal year following the date of the latest balance sheet presented in the financial statements. 2019 Future Amortization of Debt and Long Term Debt, Maturities, Repayments of Principal Fourth Full Fiscal Year The aggregate amount of amortization of debt expected to be recognized and long-term debt maturing within the fourth full fiscal year following the date of the latest balance sheet presented in the financial statements. 2020 Future Amortization of Debt and Long Term Debt, Maturities, Repayments of Principal Fifth Full Fiscal Year The aggregate amount of amortization of debt expected to be recognized and long-term debt maturing within the fifth full fiscal year following the date of the latest balance sheet presented in the financial statements. Thereafter Future Amortization of Debt and Long Term Debt, Maturities, Repayments of Principal after Fifth Full Fiscal Year The aggregate amount of amortization of debt expected to be recognized and long-term debt maturing after the fifth full fiscal year following the date of the latest balance sheet presented in the financial statements. Total amortization of debt and principal repayments Debt Instrument, Interest Rate, Stated Percentage Debt Instrument, Interest Rate, Stated Percentage Number of Years from Issuance of Debt for which Fixed Rate of Interest will be in Force Number of Years from Issuance of Debt for which Fixed Rate of Interest will be in Force Represents the number of years from the issuance of debt for which the fixed rate of interest will be in force. Statement of Financial Position [Abstract] Assets Assets [Abstract] Commercial real estate properties, at cost: Real Estate Investment Property, at Cost [Abstract] Land and land interests Land Building and improvements Investment Building and Building Improvements Building leasehold and improvements Building Leasehold Improvements, Gross Carrying amount at the balance sheet date of long-lived, depreciable asset that is an addition or improvement to assets held under lease arrangement as well as the initial investment in a leasehold interest. Properties under capital lease Capital Leased Assets, Gross Total commercial real estate properties, at cost Real Estate Investment Property, at Cost Less: accumulated depreciation Real Estate Investment Property, Accumulated Depreciation Total commercial real estate properties, net Real Estate Investment Property, Net Assets held for sale Disposal Group, Including Discontinued Operation, Assets Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Restricted cash Restricted Cash and Cash Equivalents Investments in marketable securities Marketable Securities Tenant and other receivables, net of allowance of $16,634 and $16,592 in 2017 and 2016, respectively Accounts and Notes Receivable, Net Related party receivables Due from Related Parties Deferred rents receivable, net of allowance of $24,079 and $25,203 in 2017 and 2016, respectively Deferred Rent Receivables, Net Debt and preferred equity investments, net of discounts and deferred origination fees of $16,316 and $16,705 in 2017 and 2016, respectively Investments in unconsolidated joint ventures Equity Method Investments Deferred costs, net Deferred Costs Other assets Other Assets Total assets Liabilities Liabilities [Abstract] Mortgages and other loans payable, net Secured Debt Revolving credit facility, net Unsecured term loan, net Senior Notes Unsecured Debt Unsecured Debt Accrued interest payable Accrued Interest Payable and Other Represents accrued interest and fair value of hedges entered into by the Entity. Other liabilities Other Liabilities Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Deferred revenue Deferred Revenue Capital lease obligations Capital Lease Obligations Deferred land leases payable Deferred Rent Credit Dividend and distributions payable Dividends Payable Security deposits Security Deposit Liability Liabilities related to assets held for sale Disposal Group, Including Discontinued Operation, Liabilities Junior subordinated deferrable interest debentures held by trusts that issued trust preferred securities Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust Total liabilities Liabilities Commitments and contingencies Commitments and Contingencies Noncontrolling interests in Operating Partnership Noncontrolling Interest in Operating Partnerships Limited partner interests in SLGOP (4,563 and 4,364 limited partner common units outstanding at March 31, 2017 and December 31, 2016, respectively) Limited Partners' Capital Account Preferred units Temporary Equity, Carrying Amount, Attributable to Parent Equity Stockholders Equity Including Portion Attributable to Noncontrolling Interest in Other Partnership [Abstract] -- None. No documentation exists for this element. -- Series I Preferred Stock, $0.01 par value, $25.00 liquidation preference, 9,200 issued and outstanding at both March 31, 2017 and December 31, 2016 Preferred Stock, Value, Issued Common stock, $0.01 par value, 160,000 shares authorized and 101,831 and 101,617 issued and outstanding at March 31, 2017 and December 31, 2016, respectively (including 1,055 shares held in treasury at March 31, 2017 and December 31, 2016) Common Stock, Value, Issued Additional paid-in-capital Additional Paid in Capital Treasury stock at cost Treasury Stock, Value Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Retained earnings Retained Earnings (Accumulated Deficit) Total SL Green stockholders' equity Stockholders' Equity Attributable to Parent Noncontrolling interests in other partnerships Other Noncontrolling Interests Total equity SL Green stockholders equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Series I Preferred Units, $25.00 liquidation preference, 9,200 issued and outstanding at both March 31, 2017 and December 31, 2016 Preferred Units, Preferred Partners' Capital Accounts SL Green partners' capital (1,053 and 1,049 general partner common units and 99,723 and 99,513 limited partner common units outstanding at March 31, 2017 and December 31, 2016, respectively) General And Limited Partners Capital Account General And Limited Partners Capital Account Total SLGOP partners' capital Partners' Capital Noncontrolling interests in other partnerships Partners' Capital Attributable to Noncontrolling Interest Total capital Total liabilities and equity/capital Liabilities and Equity Corporate Indebtedness Debt Disclosure [Text Block] Preferred Equity, March 2018 Preferred Equity with an Initial Mandatory Redemption Date of March 2018 [Member] Preferred Equity with an Initial Mandatory Redemption Date of March 2018 [Member] Preferred Equity, November 2018 Preferred Equity with an Initial Mandatory Redemption Date of November 2018 [Member] Preferred Equity with an Initial Mandatory Redemption Date of November 2018 [Member] Preferred equity investments Preferred Equity Investments in Mortgage Loans [Member] Represents preferred equity investments in mortgage loans on real estate. Preferred equity investment Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Third Amendment and Restated 2005 Stock Option and Incentive Plan Third Amendment and Restated 2005 Stock Option and Incentive Plan [Member] Third Amendment and Restated 2005 Stock Option and Incentive Plan [Member] Stock options, stock appreciation rights and other awards Stock Options Stock Appreciation Rights and Other Awards [Member] Represents the stock options, stock appreciation rights and other awards granted by the entity. Thes do not deliver full value and have an expiration date. All other awards Other Awards [Member] Represents awards granted by the entity that deliver the full value of the award upon vesting. Long Term Outperformance Compensation Program 2014 [Member] Long Term Outperformance Compensation Program 2014 [Member] Long Term Outperformance Compensation Program 2014 [Member] Deferred Stock Compensation Plan for Directors Deferred Stock Compensation Plan for Directors [Member] Represents the Deferred Stock Compensation Plan for Directors of the entity. Employee Stock Purchase Plan Employee Stock Purchase Plan [Member] Employee Stock Purchase Plan [Member] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Stock options Employee Stock Option [Member] Restricted Stock Awards Restricted Stock Awards [Member] Represents the restricted stock awards granted by the entity. Restricted stock are shares of stock for which sale is contractually or governmentally restricted for a given period of time. LTIP units Long Term Incentive Plan Units [Member] LTIP units as awarded by a company to its employees as a form of incentive compensation. Performance Shares [Member] Performance Shares [Member] Vesting [Axis] Vesting [Axis] Vesting [Domain] Vesting [Domain] Vesting on August 31, 2017 Share-based Compensation Award, Tranche Three [Member] Vesting on August 31, 2018 Share-based Compensation Award, Tranche Four [Member] Share-based Compensation Award, Tranche Four [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Maximum fungible units that may be granted (in shares) Share Based Compensation Arrangement by Share Based Payment Award, Number of Fungible Units Authorized Represents the maximum number of fungible units authorized to be granted by the entity. Fungible units per share (in fungible units per share) Share Based Compensation Arrangement by Share Based Payment Award, Fungible Units Per Share Share Based Compensation Arrangement by Share Based Payment Award, Fungible Units Per Share Award expiration period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Shares that may be issued if equal to fungible units (shares) (less than) Share Based Compensation Arrangement by Share Based Payment Award, Number of Shares to be Issued if Equal to Fungible Units Represents the number of shares that would be issued under the plan if shares issued is equal to fungible units; actual shares issued may be more or less depending on the type of awards issued and the ratio of fungible units to shares under each award. Fungible units Share-based Compensation Arrangement By Share-based Payment Award, Number Of Fungible Units Available For Grant Share-based Compensation Arrangement By Share-based Payment Award, Number Of Fungible Units Available For Grant Options vesting period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Period of commencement of option vesting, from date of grant (in years) Share Based Compensation Arrangement by Share Based Payment Award, Period of Award Vesting Commencement Represents the period from the date of grant of the awards for the commencement of vesting of awards. Exercise price of options granted, low end of the range (in dollars per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit Exercise price of options granted, high end of the range (in dollars per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit Remaining weighted average contractual life of the options outstanding (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Remaining average contractual life of the options exercisable (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Compensation expense Allocated Share-based Compensation Expense Total unrecognized compensation cost related to unvested stock awards Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Weighted average period for recognition of compensation cost related to unvested stock awards (in years) Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Annual award vesting rate, low end of range (as a percent) Share Based Compensation Arrangement by Share Based Payment Award, Award Vesting Rate, Low End of Range Represents the low end of the range of annual vesting rates that occurs once performance criteria are reached. Annual award vesting rate, high end of range (as a percent) Share Based Compensation Arrangement by Share Based Payment Award, Award Vesting Rate, High End of Range Represents the low end of the range of annual vesting rates that occurs once performance criteria are reached. Fair value of restricted stock vested during the period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Capitalized to assets associated with compensation expense related to our long-term compensation plans, restricted stock and stock options Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount Weighted average fair value of options granted during the period Share Based Compensation Arrangement by Share Based Payment Award, Grants in Period Fair Value Represents the weighted average fair value of awards granted during the period. Share-based Compensation Share-based Compensation LTIP units earned (in shares) Share Based Compensation, Arrangement by Share Based Payment Award, Equity Instruments Other than Options, Awards Earned Represents the awards earned by all participants under the stock based compensation plans. Percentage of units vested Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Performance period (in years) Deferred Compensation Arrangement with Individual, Requisite Service Period Award period (in years) Share-based Compensation Arrangement by Share--based Payment Award, Stock Appreciation Period Share-based Compensation Arrangement by Share--based Payment Award, Stock Appreciation Period Maximum percentage of the annual retainer fee, chairman fees and meeting fees that may be deferred by non-employee directors (percent) Deferred Compensation Arrangement with Individual Maximum Percentage of the Compensation that May be Deferred Represents the maximum percentage of the compensation that may be deferred by employees of the entity under deferred compensation plans. Awards granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Shares issued (in shares) Deferred Compensation Arrangement with Individual, Shares Issued Awards outstanding (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Shares of common stock available for issuance (shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Duration of each offering period starting the first day of each calendar quarter (in months) Share Based Compensation Arrangement by Share Based Payment Award, Duration of Offering Periods Represents the duration of each offering period during which the shares are offered for purchase under the stock-based compensation plan of the entity. Share Based Compensation Arrangement by Share Based Payment Award, Purchase Price as Percentage of Market Value of Common Stock Share Based Compensation Arrangement by Share Based Payment Award, Purchase Price as Percentage of Market Value of Common Stock Represents the price at which the employees can purchase the shares of common stock of the entity under stock-based compensation plans. Such price is expressed as a percentage of lesser of market value of the shares on the first day or the last day of the offering period under that plan. Shares of common stock issued (shares) Common Stock, Shares Held in Employee Trust, Shares Share-based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Mortgages and Other Loans Payable -- None. No documentation exists for this element. -- Schedule of first mortgages and other loans payable collateralized by the respective properties and assignment of leases Mortgage and Other Loans Payable [Table Text Block] Tabular disclosure of the information pertaining to mortgage and other loans payable of the entity. The disclosure may include but is not limited to identification of terms, features, collateral requirements and other information necessary to a fair presentation. Schedule of components of deferred costs Schedule of Deferred Costs [Table Text Block] Tabular disclosure of the components of deferred costs. Number of portfolio segments of financial receivables (segment) Financing Receivable, Portfolio Segments Number Represents the number of portfolio segments of financing receivables. Additional amount of financing receivables included in other assets Financing Receivable, Recorded in Other Assets Represents the amount of financing receivables recorded in other assets on the entity's balance sheet. Class of Treasury Stock Class of Treasury Stock [Table Text Block] Schedule of Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Schedule of Future Minimum Rental Payments for Operating Leases Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Schedule of Future Minimum Lease Payments for Capital Leases Schedule of Future Minimum Lease Payments for Capital Leases [Table Text Block] Series G Preferred Units Series G Preferred Stock [Member] Series F Preferred Units Series F Preferred Stock [Member] Series K Preferred Units Series K Preferred Stock [Member] Series K Preferred Stock [Member] Series L Preferred Units Series L Preferred Stock [Member] Series L Preferred Stock [Member] Series M Preferred Units Series M Preferred Stock [Member] Series M Preferred Stock [Member] Series N Preferred Units Series N Preferred Stock [Member] Series N Preferred Stock [Member] Series O Preferred Units Series O Preferred Stock [Member] Series O Preferred Stock [Member] Series P Preferred Units Series P Preferred Stock [Member] Series P Preferred Stock [Member] Series Q Preferred Units Series Q Preferred Stock [Member] Series Q Preferred Stock [Member] Series R Preferred Units Series R Preferred Stock [Member] Series R Preferred Stock [Member] Series S Preferred Units Series S Preferred Stock [Member] Series S Preferred Stock [Member] Series T Preferred Units Series T Preferred Units [Member] Series T Preferred Units [Member] Series U Preferred Units Series U Preferred Units [Member] Series U Preferred Units [Member] Series A Preferred Units Series A Preferred Stock [Member] Series B Preferred Units Series B Preferred Stock [Member] Organization Number of units of operating partnership owned by the noncontrolling interest unit holders (shares) Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) Common Stock Capital Shares Reserved Issuance upon Redemption of Units of Limited Partnership Represents the number of common shares reserved for issuance upon redemption of units of the limited partnership interest. Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward] Balance at beginning of period Distributions Noncontrolling Interest, Decrease from Distributions to Other Noncontrolling Interest Holders Noncontrolling Interest, Decrease from Distributions to Other Noncontrolling Interest Holders Issuance of common units Redemption of common units Net income Noncontrolling Interest in Net Income (Loss) Operating Partnerships, Redeemable Accumulated other comprehensive income allocation Fair value adjustment Minority Interest Increase (Decrease) from Fair Value Adjustment Represents the increase (decrease) in noncontrolling interest resulting from fair value adjustments. Balance at end of period Number of preferred units issued (in shares) Temporary Equity, Shares Issued Dividend rate preferred units (as a percent) Preferred Stock, Dividend Rate, Percentage Liquidation preference of preferred units (in dollars per share) Temporary Equity, Liquidation Preference Per Share Annual dividends on preferred units (in dollars per share) Preferred Stock, Dividends, Per Share, Cash Paid Operating partnership common stock value use for conversion of preferred units (in dollars per share) Operating Partnership Common Unit Value, Per Share Use for Conversion Represents the common stock value per share which is used for purposes of determining the number of operating partnership common stock issue on conversion of preferred unit. Number of company common stock issue on redemption of operation partnership common units Operating Partnership Common Unit, Convertible Conversion Ratio Operating Partnership Common Unit, Convertible Conversion Ratio Mandatory liquidation preference (in dollars per share) Temporary Equity, Liquidation Preference Preferred Units, shares authorized Preferred Units, Authorized Number of company common stock issued on conversion of Series B preferred units Preferred Stock, Convertible Conversion Ratio Preferred Stock, Convertible Conversion Ratio Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Consolidated VIEs Principles of Consolidation Variable Interest Entity [Line Items] Commercial real estate properties Income Statement [Abstract] Operating expenses, paid to related parties Affiliate Costs Investment in Marketable Securities Cost basis Available-for-sale Securities, Amortized Cost Basis Proceeds from sale of marketable securities Proceeds from Sale and Maturity of Marketable Securities, Net of Transaction Costs Proceeds from Sale and Maturity of Marketable Securities, Net of Transaction Costs Marketable Securities, Realized Gain (Loss) Marketable Securities, Realized Gain (Loss) Financial Instruments: Derivatives and Hedging Derivative Instruments and Hedging Activities Disclosure [Text Block] Landmark Square Landmark Square [Member] Represents the information pertaining to Landmark Square, a property owned by the entity. 485 Lexington Avenue Lexington Avenue, 485 [Member] Represents the information pertaining to 485 Lexington Avenue, a property owned by the entity. 762 Madison Avenue Madison Avenue 762 [Member] Represents information pertaining to property located at 762 Madison Avenue, owned by the entity. One Madison Avenue One Madison Avenue [Member] Represents information pertaining to One Madison Avenue, a property owned by the entity. 100 Church Street Church Street, 100 [Member] Represents the information pertaining to 100 Church Street, a property owned by the entity. 919 Third Avenue Third Avenue, 919 [Member] Represents the information pertaining to 919 Third Avenue, a property owned by the entity. 400 East 58th Street East 400 Street 58 [Member] Represents information pertaining to 400 East 58th Street, a property owned by the entity. 420 Lexington Avenue Lexington Avenue, 420 [Member] Represents the information pertaining to 420 Lexington Avenue, a property owned by the entity. 1515 Broadway Broadway, 1515 [Member] Represents the information pertaining to 1515 Broadway, a property owned by the entity. 885 Third Avenue Third Avenue, 885 [Member] Represents the information pertaining to 885 Third Avenue, a property owned by the entity. 719 Seventh Avenue Seven One Nine Seventh Avenue [Member] Seven One Nine Seventh Avenue [Member] 183, 187 Broadway & 5-7 Dey Street 187 Broadway and 5-7 Dey Street [Member] 187 Broadway and 5-7 Dey Street [Member] 1080 Amsterdam Amsterdam 1080 [Member] Represents the information pertaining to 1080 Amsterdam, a property owned by the entity. 315 West 33rd Street [Member] 315 West 33rd Street [Member] 315 West 33rd Street [Member] 220 East 42nd Street East 220 Street 42 [Member] Represents the information pertaining to 220 East 42nd Street, a property owned by the entity. One Vanderbilt One Vanderbilt [Member] One Vanderbilt [Member] Amsterdam Avenue 1080 [Member] Amsterdam Avenue 1080 [Member] Represents information pertaining to property located at 1080 Amsterdam, owned by the entity. FHLB Advance Maturing in January 2017 FHLB Advance Maturing in January 2017 [Member] FHLB Advance Maturing in January 2017 [Member] FHLB Advance Maturing in January 2017, 2 FHLB Advance Maturing in January 2017, 2 [Member] FHLB Advance Maturing in January 2017, 2 [Member] Unsecured Loan Unsecured Debt [Member] Master Repurchase Agreement Uncommitted Master Repurchase Agreement [Member] Represents information pertaining to the Master Repurchase Agreement. Subordinate loan Senior Subordinated Loans [Member] Construction Loans Construction Loans [Member] Series J Preferred Units Series J Preferred Stock [Member] Series J Preferred Stock [Member] Total fixed rate debt Secured Debt, Bearing Fixed Interest, Mortgage Amount Secured Debt, Bearing Fixed Interest, Mortgage Amount Secured Debt, Bearing Fixed Interest, Subordinate Loan Amount Secured Debt, Bearing Fixed Interest, Subordinate Loan Amount Secured Debt, Bearing Fixed Interest, Subordinate Loan Amount Mortgages reclassed to liabilities related to assets held for sale Secured Debt, Amount Transferred to Liabilities Related to Net Assets Held for Sale Secured Debt, Amount Transferred to Liabilities Related to Net Assets Held for Sale Total mortgages and other loans payable Secured Debt, Gross Secured Debt, Gross Deferred financing costs, net of amortization Secured Debt, Deferred Finance Costs, Net Secured Debt, Deferred Finance Costs, Net Total mortgages and other loans payable, net Interest in property (as a percent) Noncontrolling Interest, Ownership Percentage by Parent Limited partnership interest Redeemable Noncontrolling Interest, Equity, Carrying Amount Preferred Units (as a percent) Preferred Units, liquidation preference (in dollars per unit) Deferred financing costs, net of amortization Number of extension options Debt Instrument, Number of Extension Options Debt Instrument, Number of Extension Options Period of extension options Debt Instrument, Period of Extension Option Debt Instrument, Period of Extension Option Maximum facility capacity Credit facility, interest rate (as a percent) Basis Point Fee (as a percent) Line of Credit Facility, Basis Point Fee Line of Credit Facility, Basis Point Fee Threshold amount for basis point fee to be applicable (less than) Line of Credit Facility, Threshold Amount for Basis Point Fee Line of Credit Facility, Threshold Amount for Basis Point Fee Book value of collateral Collateral Already Posted, Aggregate Fair Value Schedule of Noncontrolling Interest Schedule of Noncontrolling Interest [Table Text Block] Tabular disclosure of the information pertaining to the noncontrolling interest. Schedule of Preferred Unit Activity Schedule of Preferred Units [Table Text Block] Schedule of commercial office properties Schedule of Real Estate Properties [Table Text Block] Mortgages and Other Loans Payable Mortgage Notes and Other Loans Payable Disclosure [Text Block] Description and amounts of mortgage notes and other loans payable disclosure at the end of the reporting period. This element may be used for the entire disclosure as a single block of text. Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] SL Green Realty Corp SL Green Realty Corp [Member] Represents information pertaining to the SL Green Realty Corp. Net unrealized (loss) gain on derivative instruments Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Net unrealized gain on marketable securities Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward] Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward] Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward] Beginning Balance Other comprehensive (loss) income before reclassifications Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Amounts reclassified from accumulated other comprehensive income Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Ending Balance Deferred net losses from terminated hedges Other Comprehensive Income (Loss), Deferred Net Loss from Terminated Hedges Other Comprehensive Income (Loss), Deferred Net Loss from Terminated Hedges Debt and Preferred Equity Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Earnings Per Share Earnings Per Share [Abstract] Numerator Net Income (Loss) Attributable to Parent [Abstract] Basic Earnings: Net Income (Loss) Available to Common Stockholders, Basic [Abstract] Income attributable to SL Green common stockholders Net Income (Loss) Available to Common Stockholders, Basic Effect of Dilutive Securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Redemption of units to common shares Dilutive Securities, Effect on Basic Earnings Per Share, Dilutive Convertible Securities Diluted Earnings: Net Income (Loss) Available to Common Stockholders, Diluted [Abstract] Income attributable to SL Green common stockholders Net Income (Loss) Available to Common Stockholders, Diluted Denominator Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic Shares: Weighted Average Number of Shares Outstanding, Basic [Abstract] Effect of Dilutive Securities: Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract] Operating Partnership units redeemable for common shares (shares) Incremental Common Shares, Attributable to Redemption of Units to Common Shares Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of the redemption of units to common shares. Stock-based compensation plans (shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Diluted weighted average common stock outstanding (shares) Weighted Average Number of Shares Outstanding, Diluted Segments [Axis] Segments [Domain] Subsegments [Axis] Subsegments [Axis] Subsegments [Domain] Subsegments [Domain] Subsegments Consolidation Items [Axis] Subsegments Consolidation Items [Axis] Subsegments Consolidation Items [Domain] Subsegments Consolidation Items [Domain] Segment Reporting Information [Line Items] Reconciliation of income from continuing operations to net income attributable to SL Green common stockholders Net income before equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities Equity in net gain on sale of interest in unconsolidated joint venture/real estate Equity Method Investment, Realized Gain (Loss) on Disposal Gain on sale of real estate, net Gains (Losses) on Sales of Investment Real Estate Depreciable real estate reserves Depreciable Real Estate Reserves, Effect on Earnings Depreciable Real Estate Reserves, Effect on Earnings Gain on sale of investment in marketable securities Marketable Securities, Gain (Loss) Net income Deferred leasing costs Deferred Costs, Leasing, Gross Less: accumulated amortization Accumulated Amortization of Deferred Costs The accumulated amortization, as of the reporting date, representing the periodic charge to earnings of deferred costs. Deferred costs, net Schedule of general information on joint ventures Equity Method Investments [Table Text Block] Schedule of first mortgage notes payable collateralized by the respective joint venture properties and assignment of leases Schedule of Mortgage and Other Loans Payable on Joint Venture Properties [Table Text Block] Tabular disclosure of the information pertaining to mortgage and other loans payable on joint venture properties of the entity. Schedule of combined balance sheets for the unconsolidated joint ventures Equity Method Investments, Summarized Financial Information Balance Sheet [Table Text Block] Disclosure of summarized balance sheet financial information for investments accounted for using the equity method of accounting. Schedule of combined statements of income for the unconsolidated joint ventures Equity Method Investments, Summarized Financial Information Income Statement [Table Text Block] Disclosure of summarized income statement information for investments accounted for using the equity method of accounting. Initial term of non cancellable operating leases, minimum (in years) Operating Leases, Minimum Lease Term Represents the initial minimum term of the non cancellable operating leases. Capital lease Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments, Fiscal Year Maturity [Abstract] Remaining 2017 Capital Leases, Future Minimum Payments Due, Next Twelve Months 2017 Capital Leases, Future Minimum Payments Due in Two Years 2018 Capital Leases, Future Minimum Payments Due in Three Years 2019 Capital Leases, Future Minimum Payments Due in Four Years 2020 Capital Leases, Future Minimum Payments Due in Five Years Thereafter Capital Leases, Future Minimum Payments Due Thereafter Total minimum lease payments Capital Leases, Future Minimum Payments Due Amount representing interest Capital Leases, Future Minimum Payments, Interest Included in Payments Capital lease obligations Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments Non-cancellable operating leases Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] Remaining 2017 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2017 Operating Leases, Future Minimum Payments, Due in Two Years 2018 Operating Leases, Future Minimum Payments, Due in Three Years 2019 Operating Leases, Future Minimum Payments, Due in Four Years 2020 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Total minimum lease payments Operating Leases, Future Minimum Payments Due Concentration Risk [Table] Concentration Risk [Table] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Tenant 1 Tenant 1 [Member] Represents first tenant of the entity for which a concentration risk is disclosed. Tenant 2 Tenant 2 [Member] Represents second tenant of the entity for which a concentration risk is disclosed. Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Annualized rent Annualized Rent [Member] Annualized rent, when it serves as a benchmark in a concentration of risk calculation. 1185 Avenue of the Americas Avenue of the Americas, 1185 [Member] Represents the information pertaining to 1185 Avenue of the Americas, a property owned by the entity. 1 Madison Ave 1 Madison Ave [Member] 1 Madison Ave [Member] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Customer concentration Customer Concentration Risk [Member] Concentration of Credit Risk Concentration Risk [Line Items] Number of tenants (tenants) Number of Tenants Represents the number of tenants to whom the facility is leased. Percentage of concentration (percent) Concentration Risk, Percentage Maximum percentage of annualized rent for any one tenant not individually disclosed (percent) (more than) Concentration Risk Percentage Threshold Represents the maximum percentage of concentration risk that is not individually disclosed. Deferred debt issuance costs Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Greene Street 102 [Member] Greene Street 102 [Member] Greene Street 102 [Member] White Plains Road, 520 [Member] White Plains Road, 520 [Member] Represents the information pertaining to 520 White Plains Road, a property owned by the entity. Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Depreciable Real Estate Reserves, Effect on Earnings, Attributable to Parent Depreciable Real Estate Reserves, Effect on Earnings, Attributable to Parent Depreciable Real Estate Reserves, Effect on Earnings, Attributable to Parent Joint Venture Ownership Percentage Sold Joint Venture Ownership Percentage Sold Represents the ownership percentage of the joint venture sold to the incoming partner. Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Revenues Revenues [Abstract] Rental revenue, net Operating Leases, Income Statement, Minimum Lease Revenue Escalation and reimbursement Tenant Reimbursements Investment income Investment Income, Interest and Dividend Other income Other Income Total revenues Expenses Costs and Expenses [Abstract] Operating expenses, including $4,173 in 2017 and $3,462 in 2016 of related party expenses Costs and Expenses Real estate taxes Real Estate Tax Expense Ground rent Direct Costs of Leased and Rented Property or Equipment Interest expense, net of interest income Interest Expense, Net Amount of interest expense paid, net of interest income earned by the entity, during the period. Amortization of deferred financing costs Amortization of Debt Issuance Costs Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Transaction related costs Transaction Related Costs This Element represents the transaction related costs during the period. Total expenses Total Costs and Expenses Including Nonoperating Income (Expense) This element represents the total of the costs related to real estate revenues, including management, leasing, and development services and income (expense) from ancillary business-related activities. Income (loss) before equity in net income from unconsolidated joint ventures, equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Equity in net income from unconsolidated joint ventures Income (Loss) from Equity Method Investments Net income attributable to noncontrolling interests: Net Income (Loss) Attributable to Noncontrolling Interest [Abstract] Noncontrolling interests in the Operating Partnership Noncontrolling interests in other partnerships Preferred units distributions Noncontrolling Interest in Net Income (Loss) Preferred Unit Holders, Redeemable Net income (loss) attributable to SL Green/SLGOP Net Income (Loss) Attributable to Parent Perpetual preferred stock dividends Perpetual preferred unit distributions Preferred Stock Dividends and Other Adjustments Net income attributable to SLGOP common unitholders Amounts attributable to SL Green common stockholders: Income Amounts Attributable to Parent, Disclosures [Abstract] Income before depreciable real estate reserves and gains on sale Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Equity in net gain on sale of interest in unconsolidated joint venture/real estate Gain (Loss) on Sale of Unconsolidated Joint Ventures or Real Estate Gain (Loss) on Sale of Unconsolidated Joint Ventures or Real Estate reflects the amount by which the consideration received exceeds (is exceeded by) the net carrying amount (reflecting previous provisions for loss on disposal, if any) of the disposal group. Gain on sale of real estate, net Gains (Losses) on Sales of Investment Real Estate, Attributable to Parent Gains (Losses) on Sales of Investment Real Estate, Attributable to Parent Depreciable real estate reserves Net income attributable to SL Green common stockholders Basic earnings per share: Earnings Per Share, Basic [Abstract] Income (loss) from continuing operations before depreciable real estate reserves, gains on sale and discontinued operations (in usd per share) Income (Loss) from Continuing Operations, Per Basic Share (Loss) income from continuing operations before gains on sale and discontinued operations (usd per share) Income (Loss) from Continuing Operations, Per Outstanding Limited Partnership Unit, Basic, Net of Tax Equity in net gain on sale of interest in unconsolidated joint venture/real estate (usd per share) Gain (Loss) on Sale of Unconsolidated Joint Ventures or Real Estate, Per Basic Share The amount of gain (loss) from sale of unconsolidated joint ventures or real estate per basic share. Gain on sale of real estate (in dollars per share) Gains (Losses) on Sales of Investment Real Estate, Per Basic Share Gains (Losses) on Sales of Investment Real Estate, Per Basic Share Depreciable Real Estate Reserves, Effect on Earnings, Per Basic Share Depreciable Real Estate Reserves, Effect on Earnings, Per Basic Share Depreciable Real Estate Reserves, Effect on Earnings, Per Basic Share Net income attributable to SL Green common stockholders (usd per share) Earnings Per Share, Basic Net income attributable to SLGOP common unitholders (usd per share) Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Net of Tax Diluted earnings per share: Earnings Per Share, Diluted [Abstract] Income (loss) from continuing operations before depreciable real estate reserves, gains on sale and discontinued operations (in usd per share) Income (Loss) from Continuing Operations, Per Diluted Share (Loss) income from continuing operations before gains on sale and discontinued operations (in usd per share) Income (Loss) from Continuing Operations, Net of Tax, Per Outstanding Limited Partnership Unit, Diluted Equity in net gain on sale of interest in unconsolidated joint venture/real estate (usd per share) Gain (Loss) on Sale of Unconsolidated Joint Ventures or Real Estate, Per Diluted Share The amount of gain (loss) from sale of unconsolidated joint ventures or real estate per diluted share. Gain on sale of real estate (in dollars per share) Gains (Losses) on Sales of Investment Real Estate, Per Diluted Share Gains (Losses) on Sales of Investment Real Estate, Per Diluted Share Depreciable real estate reserves (in dollars per share) Depreciable Real Estate Reserves, Effect on Earnings, Per Diluted Share Depreciable Real Estate Reserves, Effect on Earnings, Per Diluted Share Net income attributable to SL Green common stockholders (usd per share) Earnings Per Share, Diluted Net income attributable to SLGOP common unitholders (usd per share) Net Income (Loss), Net of Tax, Per Outstanding Limited Partnership Unit, Diluted Dividends per share/unit (usd per share) Basic weighted average common shares outstanding (in shares) Basic weighted average common units outstanding (in shares) Weighted Average Limited Partnership Units Outstanding, Basic Diluted weighted average common shares and common share equivalents outstanding (in shares) Diluted weighted average common units and common unit equivalents outstanding (in shares) Weighted Average Limited Partnership Units Outstanding, Diluted Employee Stock Purchase Plan [Member] Long Term Incentive Plan Units [Member] Performance Shares [Member] Common Stock, Shares Held in Employee Trust, Shares Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Dividend yield (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Expected life of option (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Risk-free interest rate (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Expected stock price volatility (as a percent) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Options Outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Balance at beginning of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures Exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Lapsed or cancelled (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Balance at end of period (in shares) Options exercisable at end of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Weighted Average Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Exercise Price [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Exercise Price [Roll Forward] Balance at beginning of year (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Granted (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Exercised (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Lapsed or cancelled (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price Balance at end of period (in dollars per share) Options exercisable at end of period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Summary of restricted stock Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Balance at beginning of year (in shares) Granted (in shares) Cancelled (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Balance at end of period (in shares) Vested during the period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Compensation expense recorded Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Principles of Consolidation Consolidation, Policy [Policy Text Block] Investment in Commercial Real Estate Properties Investment in Real Estate [Policy Text Block] Disclosure of accounting policy for investments in real estate properties. Fair Value Measurements Fair Value of Financial Instruments, Policy [Policy Text Block] Investment in Marketable Securities Marketable Securities, Policy [Policy Text Block] Investments in Unconsolidated Joint Ventures Equity Method Investments, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Reserve for Possible Credit Losses Financing Receivable, Allowance for Credit Losses, Policy or Methodology Change [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Stock-Based Employee Compensation Plans Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Earnings per Share of the Company Earnings Per Share, Policy [Policy Text Block] Earnings per Unit of the Operating Partnership Earnings Per Unit, Policy [Policy Text Block] Earnings Per Unit, Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Concentrations of Credit Risk Concentration Risk, Credit Risk, Policy [Policy Text Block] Reclassification Reclassification, Policy [Policy Text Block] Accounting Standards Updates New Accounting Pronouncements, Policy [Policy Text Block] Schedule of Real Estate Properties [Table] Schedule of Real Estate Properties [Table] Manhattan Manhattan [Member] Represents information pertaining to properties located in Manhattan. Suburban Suburban [Member] Represents information pertaining to property located in Suburban areas. Real Estate Property Ownership [Axis] Real Estate Property Ownership [Axis] Real Estate Properties [Domain] Real Estate Properties [Domain] Consolidated properties Consolidated Properties [Member] Unconsolidated properties Unconsolidated Properties [Member] Office Office Properties [Member] Represents the investment in office properties owned by the entity. Retail Retail Properties [Member] Represents information pertaining to retail properties owned by the entity. Development/Redevelopment Development Properties [Member] Represents the development properties owned by the entity. Fee Interest Fee Interest [Member] Fee Interest [Member] Commercial properties Commercial Property [Member] Commercial Property [Member] Residential Residential Real Estate [Member] Dual property type, retail portion Dual Property Type, Retail Portion [Member] Dual Property Type, Retail Portion [Member] Dual property type, residential portion Dual Property Type, Residential Portion [Member] Dual Property Type, Residential Portion [Member] Managed office properties Managed Office Properties [Member] Represents the office properties managed by the entity. Real estate properties Real Estate Properties [Line Items] Number of Properties Number of Real Estate Buildings Number of Real Estate Buildings Approximate Square Feet unaudited (sqft) Weighted Average Occupancy unaudited (as a percent) Real Estate Weighted Average Occupancy Represents the weighted average occupancy of real estate properties owned, which represents the total leased square feet divided by the total available rentable square feet. Debt and preferred equity investments including investments held by unconsolidated joint ventures Mortgage Loans on Real Estate, Commercial and Consumer, Net Including Debt Investments, Other Mortgage Loans on Real Estate, Commercial and Consumer, Net Including Debt Investments, Other Debt and preferred equity investments and other financing receivables included in other balance sheet items Debt Investments, Other Debt Investments, Other Number of shares to be received on redemption of one unit of limited partnership interests (shares) Number of Shares on Redemption of One Unit of Partnership Interest Represents the number of shares of the common stock of the entity, which the limited partner of the operating partnership is entitled to receive on redemption of one unit of interest in the partnership. Derivative [Table] Derivative [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract Type [Domain] Derivative Contract [Domain] Interest Rate Swap Expiring in December 2017 Interest Rate Swap Expiring in December 2017 7 [Member] Interest Rate Swap Expiring in December 2017 7 [Member] Interest Rate Swap Expiring in December 2017 Interest Rate Swap Expiring in December 2017 8 [Member] Interest Rate Swap Expiring in December 2017 8 [Member] Interest Rate Swap Expiring in December 2017 Interest Rate Swap Expiring in December 2017 9 [Member] Interest Rate Swap Expiring in December 2017 9 [Member] Interest Rate Cap Expiring in September 2017 Interest Rate Cap Expiring in September 2017 [Member] Interest Rate Cap Expiring in September 2017 [Member] Interest Rate Cap Expiring in May 2017 Interest Rate Cap Expiring in May 2017 [Member] Interest Rate Cap Expiring in May 2017 [Member] Interest Rate Swap Expiring in July 2023 Interest Rate Swap Expiring in July 2023 [Member] Interest Rate Swap Expiring in July 2023 [Member] Interest Rate Swap Expiring in July 2023 Interest Rate Swap Expiring in July 2023, 2 [Member] Interest Rate Swap Expiring in July 2023, 2 [Member] Interest Rate Cap Expiring in October 2017 Interest Rate Cap Expiring in October 2017 [Member] Interest Rate Cap Expiring in October 2017 [Member] Interest Rate Swaps/Caps Interest Rate Swap [Member] Financial Instruments: Derivatives and Hedging Derivative [Line Items] Notional Value Derivative Asset, Notional Amount Strike Rate (as a percent) Derivative, Fixed Interest Rate Fair Value Derivative, Fair Value, Net Derivative, Fair Value, Net Gain (loss) from changes in fair value Accumulated Other Comprehensive Income (Loss), Gain (Loss) from Changes in Fair Value Accumulated Other Comprehensive Income (Loss), Gain (Loss) from Changes in Fair Value Fair value of derivatives in a net liability position Derivative, Net Liability Position, Aggregate Fair Value Aggregate termination value Assets Needed for Immediate Settlement, Aggregate Fair Value Estimated current balance held in accumulated other comprehensive loss to be reclassified into earnings within the next 12 months Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Share of joint venture of accumulated other comprehensive loss reclassified into equity in net income from unconsolidated joint ventures within the next 12 months Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months into Equity in Net Income Represents the estimated net amount of existing gains (losses) on cash flow hedges at the reporting date expected to be reclassified to equity in net income within the next 12 months. Amount of (Loss) Gain Recognized in Other Comprehensive Loss (Effective Portion) Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss) Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion) Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net Amount of Loss Recognized into Income (Ineffective Portion) Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness Related Party Transactions [Abstract] Related Party Transactions Related Party Transactions Disclosure [Text Block] Fair Value Measurements Fair Value Disclosures [Text Block] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Alliance Building Services Alliance Building Services [Member] Represents the information pertaining to Alliance Building Services, which is a related party of the entity. Entity with Stephen L Green ownership interest Related Party Stephen L Green Interest [Member] Represents the information pertaining to an entity in which Stephen L. Green owns an interest, which is a related party of the entity. Related Party Transactions Related Party Transaction [Line Items] Profit participation from related party Related Party Transaction, Other Revenues from Transactions with Related Party Payments made for services Related Party Transaction, Expenses from Transactions with Related Party Property management fees from related party Revenue from Related Parties Amounts due from/to related parties Due from Related Parties, Unclassified [Abstract] Due from joint ventures Due from Joint Ventures Other Due from Other Related Parties Related party receivables Series I Preferred Units Series I Preferred Stock [Member] Outstanding nonredeemable series I preferred stock or outstanding series I preferred stock. Classified within stockholders' equity if nonredeemable or redeemable solely at the option of the issuer. Classified within temporary equity if redemption is outside the control of the issuer. Units outstanding (units) Noncontrolling Interests on the Company's Consolidated Financial Statements Noncontrolling Interest Disclosure [Text Block] Statement of Cash Flows [Abstract] Operating Activities Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization Equity in net income from unconsolidated joint ventures Distributions of cumulative earnings from unconsolidated joint ventures Proceeds from Equity Method Investment, Dividends or Distributions Equity in net gain on sale of interest in unconsolidated joint venture interest/real estate Depreciable real estate reserves Depreciable Real Estate Reserves, Cash Flow Effect Depreciable Real Estate Reserves, Cash Flow Effect Gain on sale of real estate, net Gain on sale of investment in marketable securities Marketable Securities, Gain (Loss), Cash Flow Effect Marketable Securities, Gain (Loss), Cash Flow Effect Deferred rents receivable Straight Line Rent Other non-cash adjustments Other Noncash Income (Expense) Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Restricted cash—operations Increase (Decrease) in Restricted Cash for Operating Activities Tenant and other receivables Increase (Decrease) in Accounts Receivable Related party receivables Increase (Decrease) in Due from Related Parties, Current Deferred lease costs Increase (Decrease) in Deferred Leasing Fees Other assets Increase (Decrease) in Other Operating Assets Accounts payable, accrued expenses and other liabilities and security deposits Increase (Decrease) in Accrued Liabilities and Other The change during the period in carrying value of accounts payable, accrued expenses and fair value of hedges, due within one year or operating cycle. Deferred revenue and land leases payable Increase (Decrease) in Deferred Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Investing Activities Net Cash Provided by (Used in) Investing Activities [Abstract] Acquisitions of real estate property Payments to Acquire Real Estate Additions to land, buildings and improvements Payments to Acquire Productive Assets Escrowed cash—capital improvements/acquisition deposits/deferred purchase price Increase (Decrease) in Restricted Cash Investments in unconsolidated joint ventures Payments to Acquire Equity Method Investments Distributions in excess of cumulative earnings from unconsolidated joint ventures Proceeds from Equity Method Investment Dividends or Distributions This item represents to disclosure of the amount of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporation. Distributions constitute a return of investment. Net proceeds from disposition of real estate/joint venture interest Proceeds from Real Estate and Real Estate Joint Ventures Proceeds from sale of marketable securities Proceeds from Sale and Maturity of Marketable Securities Other investments Payments for (Proceeds from) Investments Origination of debt and preferred equity investments Payments to Acquire Investments Repayments or redemption of debt and preferred equity investments Proceeds from Sale and Maturity of Other Investments Net cash provided by investing activities Net Cash Provided by (Used in) Investing Activities Financing Activities Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from mortgages and other loans payable Proceeds from Issuance of Secured Debt Repayments of mortgages and other loans payable Repayments of Secured Debt Proceeds from revolving credit facility and senior unsecured notes Proceeds from Other Debt Repayments of revolving credit facility and senior unsecured notes Repayments of Other Debt Proceeds from stock options exercised and DRIP issuance Proceeds from Stock Options Exercised Repurchase of common stock Payments for Repurchase of Common Stock Redemption of preferred stock Payments for Repurchase of Redeemable Preferred Stock Distributions to noncontrolling interests in other partnerships Distributions to Noncontrolling Interests Other Partnerships The cash outflow for distributions to the entity's partner from a consolidated joint venture. Contributions from noncontrolling interests in other partnerships Proceeds from Noncontrolling Interests in Other Partnerships The cash inflow from the capital received in cash from a partner in a consolidated partnership during the period. Distributions to noncontrolling interests in the Operating Partnership Distribution to Noncontrolling Interest Operating Partnership The cash outflow for distributions to partners in a partnership. Dividends/Distributions paid on common and preferred stock/units Payments of Dividends Other obligations related to mortgage loan participations Proceeds from Participating Mortgage Loan The cash inflow from participating mortgage loans and other mortgage obligations during the reporting period. Deferred loan costs and capitalized lease obligation Deferred Loan Costs and Capitalized Lease Obligation The net change during the reporting period in the finance costs incurred in connection with a loan. The capitalized lease obligation is a straight-line adjustment for ground lease obligations. Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net increase in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of year Cash and cash equivalents at end of period Supplemental Disclosure of Non-Cash Investing and Financing Activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Issuance of units in the Operating Partnership Partners' Capital Account, Sale of Units Redemption of units in the Operating Partnership for stock Partners' Capital Account, Redemptions Exchange of debt investment for equity in joint venture Transfer from Investments Transfer of restricted cash to operating cash and cash equivalents as a result of sale Transfer of Restricted Cash to Operating Cash Due to Sale Transfer of Restricted Cash to Operating Cash Due to Sale Issuance of preferred units relating to a real estate acquisition Stock Issued During Period, Value, Acquisitions Tenant improvements and capital expenditures payable Capital Expenditures Incurred but Not yet Paid Fair value adjustment to noncontrolling interest in Operating Partnership Operating Partnership Noncontrolling Interest Fair Value Adjustment Represents the fair value adjustment to the noncontrolling interest in the operating partnership. Capital lease assets Capital Leased Asset Capital Leased Asset Transfer of assets related to assets held for sale Transfer to Net Assets Held For Sale Value of assets transferred to assets held-for-sale in noncash transactions during the reporting period. Transfer of liabilities related to assets held for sale Transfer to Liabilities Related to Net Assets Held For Sale Value of liabilities transferred to liabilities related to assets held-for-sale in noncash transactions during the reporting period. Deferred leasing payable Deferred Lease Payable Deferred Lease Payable Transfer of assets related to assets held for sale Removal of Fully Depreciated Real Estate Assets Removal of Fully Depreciated Real Estate Assets Deconsolidation of a subsidiary (2) Deconsolidation Real Estate Investments Represents the change in the carrying value of real estate investments resulting from deconsolidation. Issuance of stock/units Stock Issued Issuance of SLG's common stock to consolidated joint venture Stock Issued to Joint Venture Stock Issued to Joint Venture Investment in Unconsolidated Joint Ventures Management fees, base revenue Management Fees, Base Revenue Assets Equity Method Investment, Summarized Financial Information, Assets [Abstract] Commercial real estate property, net Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance Debt and preferred equity investments, net Mortgage Loans On Real Estate Commercial And Consumer And Equity Method Investments Net The balance represents the amount of loans that are secured by real estate mortgages, offset by any reserve to cover probable credit losses on the loan portfolio and deduction of deferred fees, unamortized costs, premiums and discounts from the face amounts. Included in this account is investment in unconsolidated joint venture which reflects the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. Total assets Liabilities and members' equity Equity Method Investment, Summarized Financial Information, Liabilities and Equity [Abstract] Deferred revenue/gain Members' equity Equity Method Investment Summarized Financial Information, Equity Total liabilities and members' equity Equity Method Investment, Summarized Financial Information, Liabilities and Equity Company's investments in unconsolidated joint ventures Combined statements of income for the unconsolidated joint ventures Equity Method Investment, Summarized Financial Information, Income Statement [Abstract] Total revenues Equity Method Investment, Summarized Financial Information, Revenue Operating expenses Transaction related costs Loss on early extinguishment of debt Income (Loss) from Equity Method Investments Gains Losses on Extinguishment of Debt Represents the entity's share of the gain or loss on extinguishment of debt which is included in the equity income from unconsolidated joint ventures. Net income before gain on sale Equity Method Investment, Summarized Financial Information, Net Income (Loss) Company's equity in net income from unconsolidated joint ventures Amortization of acquired leases Senior unsecured notes Senior Unsecured Notes [Member] Senior Unsecured Notes [Member] 3.00% Senior unsecured notes maturing on October 15, 2017 Senior Unsecured Notes Due October 15, 2017 [Member] Represents senior unsecured notes maturing on October 15, 2017. 5.00% Senior unsecured notes maturing on August 15, 2018 Senior Unsecured Notes, Due August 15, 2018 [Member] Represents senior unsecured notes bearing an interest rate of 5 percent maturing on August 15, 2018. 7.75% Senior unsecured notes maturing on March 15, 2020 Senior Unsecured Notes Due March 15, 2020 [Member] Represents senior unsecured notes maturing on March 15, 2020. 4.50% Senior unsecured notes maturing on December 1, 2022 Senior Unsecured Notes Due December 1, 2022 [Member] Represents senior unsecured notes bearing an interest rate of 4.50 percent maturing on December 1, 2022. 4.27% Senior unsecured notes maturing on December 17, 2025 Senior Unsecured Note Due December 17, 2025 [Member] Senior Unsecured Note Due December 17, 2025 [Member] Debt disclosures by scheduled maturity date Debt Instrument, Information by Scheduled Maturity Date of Debt [Abstract] -- None. No documentation exists for this element. -- Unpaid Principal Balance Long-term Debt, Gross Accreted Balance Accreted Balance, Net of Deferred Financing Costs Senior Notes, Net of Deferred Finance Costs Senior Notes, Net of Deferred Finance Costs Coupon Rate (as a percent) Premium on sale price to calculate exchange price of notes (as a percent) Debt Instrument, Convertible, Conversion Price Premium on Common Stock Represents the percentage of premium added to the last reported sale price of the common stock of the entity to arrive at the conversion price of the debt instrument. Exchange price (in dollars per share) Debt Instrument, Convertible, Conversion Price Adjusted exchange rate for the debentures (in shares) Debt Instrument, Convertible, Conversion Ratio Principal amount of debentures, basis for conversion Debt Instrument, Convertible Principal Amount For Conversion Ratio Debt Instrument, Convertible Principal Amount For Conversion Ratio Amount of convertible debt recorded in equity Debt Instrument, Convertible, Carrying Amount of Equity Component Debt Instrument, Unamortized Discount Debt Instrument, Unamortized Premium Series I Preferred Stock Tenant and other receivables, allowance Allowance for Doubtful Accounts, Premiums and Other Receivables Deferred rents receivable, allowance Allowance for Deferred Rents Receivable The valuation allowances attributable to, for instance, credit risk associated with a lessee as of the balance sheet date to reduce the gross amount of deferred rents receivable, which would be presented in parentheses on the face of the balance sheet. Debt and preferred equity investments, discount and deferred origination fees Discount of Structured Finance Investments This item represents the net amount of discounts related to investments in structured finance investments. Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, liquidation preference (in dollars per share) Preferred Stock, Liquidation Preference Per Share Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Limited partner interests in Operating Partnership, limited partner common units outstanding (shares) Limited Partners' Capital Account, Units Outstanding Preferred units, liquidation preference (in dollars per share) Preferred units, shares issued Preferred units, shares outstanding Temporary Equity, Shares Outstanding Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, shares issued (in shares) Common Stock, Shares, Issued Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Treasury stock, shares (in shares) Treasury Stock, Shares SL Green partner's capital, general partner common units outstanding (shares) General Partners' Capital Account, Units Outstanding SL Green partners' capital, limited partner common units outstanding (shares) Limited Partnership Units Held by General Partner This element represents Limited Partnership Units Held by General Partner. Accumulated Other Comprehensive Loss of the Company/Operating Partnership Class of Treasury Stock [Table] Class of Treasury Stock [Table] Share Repurchase Program [Axis] Share Repurchase Program [Axis] Share Repurchase Program [Domain] Share Repurchase Program [Domain] Equity, Class of Treasury Stock [Line Items] Equity, Class of Treasury Stock [Line Items] Stock Repurchased During Period, Shares Stock Repurchased During Period, Shares Stock Repurchase Program, Authorized Amount Stock Repurchase Program, Authorized Amount Treasury Stock Acquired, Average Cost Per Share Treasury Stock Acquired, Average Cost Per Share Stock Repurchase Program, Remaining Authorized Repurchase Amount Stock Repurchase Program, Remaining Authorized Repurchase Amount Authorized capital stock (shares) Total Shares Authorized The maximum number of total capital shares permitted to be issued by an entity's charter and bylaws. Authorized shares, par value (in dollars per share) Total Par or Stated Value Per Share Face amount or stated value of capital stock per share; generally not indicative of the fair market value per share. Excess stock, shares authorized (shares) Excess Stock, Shares Authorized Excess stock, par value (in dollars per share) Excess Stock, Par or Stated Value Per Share Face amount or stated value of excess stock per share, which is generally not indicative of the fair market value per share. Preferred stock, shares authorized (shares) Preferred Stock, Shares Authorized Excess shares issued (shares) Excess Stock, Shares Issued Dividend Reinvestment and Stock Purchase Plan (DRIP) Dividend Reinvestment and Stock Purchase Plan [Member] Represents the dividend reinvestment and stock purchase plan of the entity. Shares, Outstanding Perpetual Preferred stock, liquidation preference (in dollars per share) Perpetual Preferred stock, annual dividends per share (in dollars per share) Preferred Stock, Dividend Rate, Per-Dollar-Amount Contributions of net proceeds from sale of preferred stock Proceeds from Issuance of Preferred Stock and Preference Stock Schedule of amounts due from/to related parties Schedule of Receivables from Related Parties [Table Text Block] Tabular disclosure of the information pertaining to amounts due from related parties. Schedule of calculation of numerator and denominator in earnings per unit Schedule of Calculation of Numerator and Denominator in Earnings Per Unit [Table Text Block] Schedule of Calculation of Numerator and Denominator in Earnings Per Unit [Table Text Block]