Debt - Summary of Outstanding Debt (Parenthetical) (Details) - USD ($)			6 Months Ended
	May 03, 2017	Jan. 19, 2017	Jun. 30, 2017
One Market Plaza [Member]
Debt Instrument [Line Items]
Ownership interest rate of property			49.00%
Prepayment cost related to mortgage loan		$ 2,715,000
1633 Broadway [Member] | Mortgages and Notes Payable with Variable Rate [Member]
Debt Instrument [Line Items]
Additional Borrowing Capacity Subject To Performance Hurdles			$ 250,000,000
Additional Borrowing Capacity Interest Rate Description			LIBOR plus 175 basis points
1633 Broadway [Member] | Mortgages and Notes Payable with Variable Rate [Member] | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Fixed/Variable Rate			1.75%
One Eight Nine Nine Pennsylvania Avenue and Liberty Place [Member] | Mortgages and Notes Payable with Fixed Rate [Member]
Debt Instrument [Line Items]
Prepayment cost related to mortgage loan	$ 5,162,000