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Subsequent Events subsequent Events (Details) | Apr. 24, 2017 USD ($) | May 01, 2017 USD ($) ft² | Apr. 23, 2017 USD ($) | Apr. 21, 2017 apartments | Apr. 19, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
--- | --- | --- | --- | --- | --- | --- | ---
Subsequent Event [Line Items] |  |  |  |  |  |  |
Secured Debt |  |  |  |  |  | $ 2,046,959,000 | $ 2,063,087,000
MacArhur BART Station [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |
Number of apartment units that could potentially be built under an option agreement | apartments |  |  |  | 402 |  |  |
767 5th Avenue (The General Motors Building) [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |
Effective Percentage | 3.65% |  |  |  |  |  |
Ownership Percentage by the Company | 60.00% |  |  |  |  |  |
Secured Debt | $ 2,300,000,000 |  |  |  |  |  |
Coupon/Stated Rate | 3.43% |  |  |  |  |  |
30 Shattuck Road [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |
Contractual Sales Price |  |  |  |  | $ 5,000,000 |  |
Revolving Credit Facility [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity | $ 1,500,000,000 |  | $ 1,000,000,000 |  |  |  |
Line of Credit Facility, Commitment Fee Percentage | 0.15% |  |  |  |  |  |
Delayed Draw Facility [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity | $ 500,000,000 |  |  |  |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage | 0.15% |  |  |  |  |  |
Current credit rating [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |
Margin added to Calculated Interest Rate | 0.875% |  |  |  |  |  |
Current credit rating [Member] | Delayed Draw Facility [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity | $ 0 |  |  |  |  |  |
Margin added to Calculated Interest Rate | 0.95% |  |  |  |  |  |
Interest Rate Swap [Member] | 767 5th Avenue (The General Motors Building) [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |
Notional Amount | $ 450,000,000 |  |  |  |  |  |
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion | $ 14,400,000 |  |  |  |  |  |
103 Carnegie Center [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |
Purchase price |  | $ 15,800,000 |  |  |  |  |
Net Rentable Area (in sf) | ft² |  | 96,000 |  |  |  |  |

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