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Investments in Unconsolidated Joint Ventures - Mortgages and Other Loans Payable (Details) | 6 Months Ended |
--- | --- | ---
Jun. 30, 2018 USD ($) extension | Dec. 31, 2017 USD ($)
Debt Instrument [Line Items] |  |
Total fixed rate debt | $ 1,861,696,000 | $ 2,400,560,000
Total floating rate debt | 677,000,000 | 465,431,000
Total fixed rate and floating rate debt | 2,538,696,000 | 2,865,991,000
919 Third Avenue |  |
Debt Instrument [Line Items] |  |
Total fixed rate debt | $ 0 | 500,000,000
1515 Broadway |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 56.87% |
Worldwide Plaza |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 24.35% |
Joint venture |  |
Debt Instrument [Line Items] |  |
Total fixed rate debt | $ 6,026,624,000 | 5,569,138,000
Total floating rate debt | 3,518,038,000 | 3,979,066,000
Total fixed rate and floating rate debt | 9,544,662,000 | 9,548,204,000
Deferred financing costs, net | (110,924,000) | (136,103,000)
Total joint venture mortgages and other loans payable, net | $ 9,433,738,000 | 9,412,101,000
Joint venture | 521 Fifth Avenue |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 50.50% |
Interest rate, fixed rate debt (as a percent) | 3.73% |
Total fixed rate debt | $ 170,000,000 | 170,000,000
Joint venture | 717 Fifth Avenue |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 10.92% |
Joint venture | 717 Fifth Avenue | Mortgage loan |  |
Debt Instrument [Line Items] |  |
Interest rate, fixed rate debt (as a percent) | 4.45% |
Total fixed rate debt | $ 300,000,000 | 300,000,000
Committed amount | $ 300,000,000 |
Joint venture | 717 Fifth Avenue | Mezzanine loans |  |
Debt Instrument [Line Items] |  |
Interest rate, fixed rate debt (as a percent) | 5.50% |
Total fixed rate debt | $ 355,328,000 | 355,328,000
Committed amount | $ 355,300,000 |
Joint venture | 650 Fifth Avenue |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 50.00% |
Joint venture | 650 Fifth Avenue | Mortgage loan |  |
Debt Instrument [Line Items] |  |
Interest rate, fixed rate debt (as a percent) | 4.46% |
Total fixed rate debt | $ 210,000,000 | 210,000,000
Long-term debt, carrying value | $ 210,000,000 |
Joint venture | 650 Fifth Avenue | Mezzanine loans |  |
Debt Instrument [Line Items] |  |
Interest rate, fixed rate debt (as a percent) | 5.45% |
Total fixed rate debt | $ 65,000,000 | 65,000,000
Joint venture | 21 East 66th Street |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 32.28% |
Interest rate, fixed rate debt (as a percent) | 3.60% |
Interest rate, floating rate debt (as a percent) | 2.75% |
Total fixed rate debt | $ 12,000,000 | 12,000,000
Total floating rate debt | $ 1,608,000 | 1,648,000
Joint venture | 919 Third Avenue |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 51.00% |
Interest rate, fixed rate debt (as a percent) | 5.12% |
Total fixed rate debt | $ 500,000,000 | 0
Joint venture | 3 Columbus Circle |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 48.90% |
Interest rate, fixed rate debt (as a percent) | 3.61% |
Total fixed rate debt | $ 350,000,000 | 350,000,000
Joint venture | 1515 Broadway |  |
Debt Instrument [Line Items] |  |
Interest rate, fixed rate debt (as a percent) | 3.93% |
Total fixed rate debt | $ 864,238,000 | 872,528,000
Joint venture | 11 Madison Avenue |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 60.00% |
Interest rate, fixed rate debt (as a percent) | 3.84% |
Total fixed rate debt | $ 1,400,000,000 | 1,400,000,000
Joint venture | 800 Third Avenue |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 60.52% |
Interest rate, fixed rate debt (as a percent) | 3.37% |
Total fixed rate debt | $ 177,000,000 | 177,000,000
Joint venture | East 400 Street 57 |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 41.00% |
Interest rate, fixed rate debt (as a percent) | 3.00% |
Total fixed rate debt | $ 100,000,000 | 100,000,000
Joint venture | Worldwide Plaza |  |
Debt Instrument [Line Items] |  |
Interest rate, fixed rate debt (as a percent) | 3.98% |
Total fixed rate debt | $ 1,200,000,000 | 1,200,000,000
Joint venture | Stonehenge Portfolio |  |
Debt Instrument [Line Items] |  |
Interest rate, fixed rate debt (as a percent) | 4.20% |
Interest rate, floating rate debt (as a percent) | 1.40% |
Total fixed rate debt | $ 323,058,000 | 357,282,000
Total floating rate debt | 38,000,000 | 55,340,000
Joint venture | 1745 Broadway |  |
Debt Instrument [Line Items] |  |
Total floating rate debt | $ 0 | 345,000,000
Joint venture | 55 West 46th Street |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 25.00% |
Interest rate, floating rate debt (as a percent) | 2.13% |
Total floating rate debt | $ 174,430,000 | 171,444,000
Committed amount | 195,000,000 |
Unused borrowing capacity, amount | 20,600,000 |
Joint venture | 175-225 Third Street Brooklyn, New York |  |
Debt Instrument [Line Items] |  |
Total floating rate debt | 0 | 40,000,000
Joint venture | Jericho Plaza |  |
Debt Instrument [Line Items] |  |
Total floating rate debt | $ 0 | 81,099,000
Joint venture | 724 Fifth Avenue |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 50.00% |
Interest rate, floating rate debt (as a percent) | 2.42% |
Total floating rate debt | $ 275,000,000 | 275,000,000
Joint venture | 1552 Broadway |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 50.00% |
Interest rate, floating rate debt (as a percent) | 2.65% |
Total floating rate debt | $ 195,000,000 | 195,000,000
Joint venture | 280 Park Avenue |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 50.00% |
Interest rate, floating rate debt (as a percent) | 1.73% |
Total floating rate debt | $ 1,200,000,000 | 1,200,000,000
Joint venture | 121 Greene Street |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 50.00% |
Interest rate, floating rate debt (as a percent) | 1.50% |
Total floating rate debt | $ 15,000,000 | 15,000,000
Joint venture | 10 East 53rd Street |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 55.00% |
Interest rate, floating rate debt (as a percent) | 2.25% |
Total floating rate debt | $ 170,000,000 | 170,000,000
Joint venture | 131-137 Spring Street |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 20.00% |
Interest rate, floating rate debt (as a percent) | 1.55% |
Total floating rate debt | $ 141,000,000 | 141,000,000
Joint venture | 11 West 34th Street |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 30.00% |
Interest rate, floating rate debt (as a percent) | 1.45% |
Total floating rate debt | $ 23,000,000 | 23,000,000
Joint venture | 100 Park Avenue |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 49.90% |
Interest rate, floating rate debt (as a percent) | 1.75% |
Total floating rate debt | $ 360,000,000 | 360,000,000
Joint venture | One Vanderbilt |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 71.01% |
Interest rate, floating rate debt (as a percent) | 3.50% |
Total floating rate debt | $ 375,000,000 | 355,535,000
Joint venture | One Vanderbilt | Construction Loans |  |
Debt Instrument [Line Items] |  |
Maximum facility capacity | $ 1,500,000,000.0 |
Credit facility, interest rate (as a percent) | 3.50% |
Term (in Years) | 5 years |
Number of extension options | extension | 2 |
Period of extension options | 1 year |
Joint venture | 605 West 42nd Street |  |
Debt Instrument [Line Items] |  |
Economic Interest (as a percent) | 20.00% |
Interest rate, floating rate debt (as a percent) | 1.44% |
Total floating rate debt | $ 550,000,000 | $ 550,000,000
Mezzanine Loan, Initial Maturity October 2022 [Member] | Joint venture | 650 Fifth Avenue | Mezzanine loans |  |
Debt Instrument [Line Items] |  |
Long-term debt, carrying value | 65,000,000 |
Secured Debt, Initial Maturity August 2019 | Joint venture | Stonehenge Portfolio |  |
Debt Instrument [Line Items] |  |
Total fixed rate debt | 135,700,000 |
Secured Debt, Initial Maturity June 2024 | Joint venture | Stonehenge Portfolio |  |
Debt Instrument [Line Items] |  |
Total fixed rate debt | 54,800,000 |
Secured Debt, Initial Maturity April 2028 | Joint venture | Stonehenge Portfolio |  |
Debt Instrument [Line Items] |  |
Total fixed rate debt | $ 132,600,000 |

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