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Debt (Details) $ in Thousands |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 07, 2017 USD ($) | Apr. 24, 2017 USD ($) mo | Sep. 30, 2017 USD ($) | Sep. 30, 2016 USD ($) | Sep. 30, 2017 USD ($) yr | Sep. 30, 2016 USD ($) | Dec. 31, 2008 USD ($) | Jun. 06, 2017 | Apr. 23, 2017 USD ($) | Dec. 31, 2016 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Proceeds from mortgage notes payable |  |  |  |  | $ 2,300,000 | $ 0 |  |  |  |
Interest Payable |  |  | $ 99,100 |  | 99,100 |  |  |  |  | $ 243,933
Outside members’ notes payable |  |  | 0 |  | 0 |  |  |  |  | $ 180,000
Repayments of mortgage notes payable |  |  |  |  | 1,313,890 | 1,323,284 |  |  |  |
Repayments of Mezzannine notes payable |  |  |  |  | 306,000 | 0 |  |  |  |
Gains from early extinguishments of debt |  |  | $ 0 | $ (371) | $ 14,354 | $ (371) |  |  |  |
767 Fifth Avenue (the General Motors Building) |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Gains from early extinguishments of debt | $ 14,600 |  |  |  |  |  |  |  |  |
767 Fifth Avenue (the General Motors Building) | Secured Debt [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Coupon/Stated Rate |  | 3.43% |  |  |  |  |  |  |  |
767 Fifth Avenue (the General Motors Building) | Members' notes Payables [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Repayment of a portion of members loans accrued interest and principal balance | 176,100 |  |  |  |  |  |  |  |  |
Consolidation, Eliminations [Member] | 767 Fifth Avenue (the General Motors Building) | Other Mezzanine Debt [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Repayments of Other Mezzanine Debt |  |  |  |  |  |  | $ 263,100 |  |  |
Consolidated Entities [Member] | 767 Fifth Avenue (the General Motors Building) |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Unpaid principal balance of the members' notes payable contributed to equity | $ 273,900 |  |  |  |  |  |  |  |  |
Consolidated Entities [Member] | 767 Fifth Avenue (the General Motors Building) | Secured Debt [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Ownership Percentage by the Company | 60.00% |  |  |  |  |  |  |  |  |
Proceeds from mortgage notes payable | $ 2,300,000 |  |  |  |  |  |  |  |  |
Coupon/Stated Rate | 3.43% |  |  |  |  |  |  | 5.95% |  |
Repayments of mortgage notes payable | $ 1,300,000 |  |  |  |  |  |  |  |  |
Consolidated Entities [Member] | 767 Fifth Avenue (the General Motors Building) | Mezzanine Debt [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Coupon/Stated Rate | 6.02% |  |  |  |  |  |  |  |  |
Repayments of Mezzannine notes payable | $ 306,000 |  |  |  |  |  |  |  |  |
Consolidated Entities [Member] | 767 Fifth Avenue (the General Motors Building) | Other Mezzanine Debt [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Other Long-term Debt | $ 294,000 |  |  |  |  |  |  |  |  |
Coupon/Stated Rate | 6.02% |  |  |  |  |  |  |  |  |
Consolidated Entities [Member] | 767 Fifth Avenue (the General Motors Building) | Members' notes Payables [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Coupon/Stated Rate | 11.00% |  |  |  |  |  |  |  |  |
Interest Payable | $ 425,000 |  |  |  |  |  |  |  |  |
Outside members’ notes payable | 450,000 |  |  |  |  |  |  |  |  |
Consolidated Entities [Member] | Consolidation, Eliminations [Member] | 767 Fifth Avenue (the General Motors Building) |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Unpaid principal balance of the members' notes payable contributed to equity | 164,400 |  |  |  |  |  |  |  |  |
Consolidated Entities [Member] | Consolidation, Eliminations [Member] | 767 Fifth Avenue (the General Motors Building) | Members' notes Payables [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest Payable | 255,000 |  |  |  |  |  |  |  |  |
Outside members’ notes payable | 270,000 |  |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Competitive bid quote |  | 65.00% |  |  |  |  |  |  |  |
Maximum Leverage Ratio |  |  |  |  | 60.00% |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 1,500,000 |  |  |  |  |  |  | $ 1,000,000 |
Leverage Ratio Maximum Increasing Limit |  |  |  |  | 65.00% |  |  |  |  |
Leverage Ratio Reduction Limit |  |  |  |  | 60.00% |  |  |  |  |
Leverage Ratio Reduction Period, Years | yr |  |  |  |  | 1 |  |  |  |  |
Maximum Secured Debt Leverage Ratio |  |  |  |  | 55.00% |  |  |  |  |
Fixed Charge Coverage Ratio Minimum. |  |  | 1.40 |  | 1.40 |  |  |  |  |
Maximum Unsecured Debt Leverage Ratio |  |  |  |  | 60.00% |  |  |  |  |
Unsecured Debt Leverage Ratio Maximum Increasing Limit |  |  |  |  | 65.00% |  |  |  |  |
Unsecured Debt Leverage Ratio Reduction Limit |  |  |  |  | 60.00% |  |  |  |  |
Unsecured Debt Leverage Ratio Reduction Period, Years | yr |  |  |  |  | 1 |  |  |  |  |
Unsecured Debt Interest Coverage Ratio Minimum. |  |  |  |  | 1.75 |  |  |  |  |
Revolving Credit Facility [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage |  | 0.10% |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage |  | 0.30% |  |  |  |  |  |  |  |
Delayed Draw Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage |  | 0.15% |  |  |  |  |  |  |  |
Line of Credit Facility, Frequency of Commitment Fee Payment |  | 4 |  |  |  |  |  |  |  |
minimum borrowing amount |  | $ 50,000 |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 500,000 |  |  |  |  |  |  |  |
Alternative Base Interest Rate Calculation [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Amount added to Federal Funds Rate to Calculate Interest Rate |  | 0.50% |  |  |  |  |  |  |  |
LIBOR Period Used to Calculate Interest Rate (in months) | mo |  | 1 |  |  |  |  |  |  |  |
Amount added to LIBOR to Calculate Interest Rate |  | 1.00% |  |  |  |  |  |  |  |
Alternative Base Interest Rate Calculation [Member] | Revolving Credit Facility [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  | 0.00% |  |  |  |  |  |  |  |
Alternative Base Interest Rate Calculation [Member] | Revolving Credit Facility [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  | 0.55% |  |  |  |  |  |  |  |
Alternative Base Interest Rate Calculation [Member] | Delayed Draw Facility [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  | 0.00% |  |  |  |  |  |  |  |
Alternative Base Interest Rate Calculation [Member] | Delayed Draw Facility [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  | 0.75% |  |  |  |  |  |  |  |
Interest Rate Based on LIBOR or CDOR [Member] | Revolving Credit Facility [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  | 0.775% |  |  |  |  |  |  |  |
Interest Rate Based on LIBOR or CDOR [Member] | Revolving Credit Facility [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  | 1.55% |  |  |  |  |  |  |  |
Interest Rate Based on LIBOR or CDOR [Member] | Delayed Draw Facility [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  | 0.85% |  |  |  |  |  |  |  |
Interest Rate Based on LIBOR or CDOR [Member] | Delayed Draw Facility [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  | 1.75% |  |  |  |  |  |  |  |
Current credit rating [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage |  |  |  |  | 0.15% |  |  |  |  |
Current credit rating [Member] | Alternative Base Interest Rate Calculation [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  |  | 0.00% |  | 0.00% |  |  |  |  |
Current credit rating [Member] | Alternative Base Interest Rate Calculation [Member] | Delayed Draw Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  |  | 0.00% |  | 0.00% |  |  |  |  |
Current credit rating [Member] | Interest Rate Based on LIBOR or CDOR [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  |  | 0.875% |  | 0.875% |  |  |  |  |
Current credit rating [Member] | Interest Rate Based on LIBOR or CDOR [Member] | Delayed Draw Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Margin added to Calculated Interest Rate |  |  | 0.95% |  | 0.95% |  |  |  |  |
Parent Company [Member] | Consolidated Entities [Member] | 767 Fifth Avenue (the General Motors Building) | Members' notes Payables [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest Payable | 170,000 |  |  |  |  |  |  |  |  |
Outside members’ notes payable | $ 180,000 |  |  |  |  |  |  |  |  |

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