Revolving Credit Facility (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended	12 Months Ended		1 Months Ended
	Nov. 30, 2011	Dec. 31, 2011	Sep. 30, 2011	Nov. 30, 2011 Wells Fargo et al. [Member]	Dec. 31, 2011 Wells Fargo et al. [Member]	Nov. 30, 2011 Cancelled Credit Facility [Member]	Oct. 31, 2011 Cancelled Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity				$ 200,000
Number of basis points over LIBOR				150		250
Revolving credit facility interest rate					1.78%
Increase in total credit facility				300,000
Borrowings on term loan		50,000
Derivative, Fixed Interest Rate			3.98%
LineOfCreditFacilityAmountOutstanding					97,300		80,125
Borrowings under revolving credit facility			48,125
Unused balance of the unsecured revolving credit facility					102,700
Interest Expense		2,070
Amortization of loan costs		581
Term Loan Maturity	four
Line of Credit Facility, Unused Capacity, Commitment Fee Basis Points				35
Debt Instrument, Maturity Date Range, End, Extension				five
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments		$ (1,197)