Historic Tax Credit (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Aug. 27, 2010 USD ($)	Nov. 17, 2008 ft²
Tax Credit Carryforward [Line Items]
Tax credit transaction income	$ (11,853)	$ (11,853)	$ (11,853)	$ (11,853)
Historic Tax Credit Transaction [Member]
Tax Credit Carryforward [Line Items]
Area Of IRS Campus Building | ft²							862,692
Percentage Of Building Leased To IRS							100.00%
Purchase Price for Non-controlling Interest Obligation Put Option			$ 3,200
Rate of Return on Noncontrolling Interest			2.00%
Accretion of Non Controlling Interest Liability			$ 1,100		$ 1,100
Percentage Of Tax Credit Recapture			20.00%
Tax credit transaction income			$ 11,900
Other Income (Expense)			(500)
Contribution allocated in non controlling interest					3,000
Deferred Costs	0		0		500
U S B [Member] | Historic Tax Credit Transaction [Member]
Tax Credit Carryforward [Line Items]
Agreed contribution in project cost						$ 64,100
USB contributions	$ 0		0		$ 15,100
Other Liabilities [Member] | Historic Tax Credit Transaction [Member]
Tax Credit Carryforward [Line Items]
Preferred Return			$ 1,000