Summary of Significant Accounting Policies (Additional Information 1) (Details) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Unsecured Revolving Credit Facility [Member]	Sep. 30, 2013 Unsecured Revolving Credit Facility [Member]	Sep. 30, 2014 Unsecured Revolving Credit Facility [Member]	Sep. 30, 2013 Unsecured Revolving Credit Facility [Member]	Sep. 30, 2014 Richmond Credit Facility [Member]	Sep. 30, 2014 Interest Rate Swap [Member] Cash Flow Hedging [Member]	Feb. 29, 2012 Interest Rate Swap [Member] Cash Flow Hedging [Member]	Feb. 08, 2012 Interest Rate Swap [Member] Cash Flow Hedging [Member]
Summary Of Significant Accounting Policies [Line Items]
Impairment losses	$ 0	$ 0	$ 0	$ 0
Amortization of the deferred financing costs			1,894,000			500,000	600,000	1,700,000	2,200,000
Written off unamortized debt cost	500,000			0
Written off unamortization cost relation to assets securitization				3,300,000						100,000
Amortization of deferred leasing costs totaled	1,800,000	1,100,000	4,600,000	3,200,000
Deferred income	9,529,000		9,529,000		7,892,000
Repayment of credit facility						75,000,000
Amortization of deferred revenue	1,100,000	1,300,000	3,500,000	3,500,000
Derivative liability					453,000						0
Notional amount of derivative												150,000,000	150,000,000
Company recorded equity-based compensation expense net of repurchased awards	900,000	500,000	2,900,000	1,300,000
Amount of the straight-line rent receivable on the balance sheets included in rents and other receivables	$ 4,200,000		$ 4,200,000		$ 2,900,000