Commitments and Contingencies (Textual) (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2004 USD ($)	Dec. 31, 2015 USD ($) ft²	Dec. 03, 2015 USD ($)	Dec. 31, 2014 USD ($)
Property Subject to or Available for Operating Lease [Line Items]
Associated letter of credit		$ 10.0		$ 0.0
Leased Area Of Building | ft²		708,844
Amount to be paid if the Company takes fee title to Two Logan Square upon foreclosure of related mortgage		$ 2.9
Liability related to acquisition of TRC	$ 0.7	$ 2.0
Agreed holding period (not to sell) for properties acquired as part of the TRC acquisition		15 years
Subaru of America [Member]
Property Subject to or Available for Operating Lease [Line Items]
NTE Amount			$ 77.3
One Commerce Square [Member]
Property Subject to or Available for Operating Lease [Line Items]
Tax guarantee obligation		$ 125.0
Two Commerce Square [Member]
Property Subject to or Available for Operating Lease [Line Items]
Tax guarantee obligation		$ 100.0
Prentiss Properties Trust [Member] | Commerce Square [Member]
Property Subject to or Available for Operating Lease [Line Items]
Non-controlling interest, ownership percentage by non-controlling Owners		1.00%
Minimum [Member]
Property Subject to or Available for Operating Lease [Line Items]
Lease terms		5 years
Maximum [Member]
Property Subject to or Available for Operating Lease [Line Items]
Lease terms		75 years