Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended				12 Months Ended
	Sep. 30, 2004	Dec. 31, 2013 sqft Y	Dec. 31, 2013 One Commerce Square [Member]	Dec. 31, 2013 Two Commerce Square [Member]	Dec. 31, 2013 One and Two Commerce Square [Member]	Dec. 31, 2013 Historic Tax Credit Transaction [Member]	Dec. 31, 2012 Historic Tax Credit Transaction [Member]	Dec. 31, 2011 Historic Tax Credit Transaction [Member]	Dec. 31, 2013 New Markets Tax Credit Transaction [Member]
Long-term Purchase Commitment [Line Items]
Accretion Of Non Controlling Interest Liability						$ 1.4	$ 1.3	$ 1.3
Commitments and Contingencies (Textuals) [Abstract]
Minimum remaining lease period		15
Maximum remaining lease period		75
Leased Area Of Building		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	1.6
Agreed holding period (not to sell) for properties acquired as part of the TRC acquisition		15 years
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners					1.00%
Tax guarantee obligation			130.0	107.9
Tax Credit Carryforward, Amount									$ 7.8