Credit Agreement and Term Loan Agreement (Details) (USD $)	6 Months Ended
	Jun. 30, 2012	Mar. 09, 2012	Dec. 31, 2011
Line of Credit Facility [Line Items]
Senior secured revolving credit agreement		$ 175,000,000
Senior secured revolving credit agreement, expiration date	Mar. 09, 2013
Annual bearing interest rate for credit agreement	3.25%
Credit Agreement Borrowing base rate	2.00%
Annual commitment fee on undrawn funds	0.40%
Percentage of equity issuance net proceeds used to pay down bank commitment	50.00%
Amount of rate increase in case of default	200
Time period of extending maturity date of loan	6 months
Debt Instrument, Maturity Date Range, End	Mar. 31, 2013
Borrowings under credit agreement	151,700,000		147,700,000
Fair value of borrowings outstanding under the credit agreement	151,700,000
Term loan borrowings	22,420,000		22,810,000
Term loan borrowings, annual reductions	780,000
Term loan balloon payment payable	21,900,000
Term loan agreement LIBOR rate of interest	30 day LIBOR
Amount of rate increase in case of default	300
Term Loan Agreement, fair value of outstanding borrowings	22,400,000
Amount of amended term loan agreement with TD Bank	25,000,000
Interest rate of term loan	3.50%
LIBOR [Member]
Line of Credit Facility [Line Items]
Credit Agreement Borrowing LIBOR rate	3.00%
Term Loan [Member]
Line of Credit Facility [Line Items]
Total Bank Syndicate commitment allocated to Term Loan	125,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Total Bank Syndicate commitment allocated to a revolving facility	50,000,000
Minimum [Member]
Line of Credit Facility [Line Items]
Minimum aggregate value of mortgage lien	$ 220,000,000
Term Loan Agreement rate floor	0.40%
Maximum [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Term Loan Agreement Borrowing LIBOR rate	3.10%