Revolving Credit Facility (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Apr. 20, 2011
Line of Credit Facility [Line Items]
Revolving credit facility amount		$ 125,000,000
Maturity date of credit facility	April 20, 2015
Maximum additional borrowings in credit facility	100,000,000
Leverage ratio	2.75
Interest coverage ratio	3.0
Interest on credit facility	300,000
Capitalized debt issuance costs	1,900,000
Capitalized debt issuance costs remaining	1,600,000
Debt issuance costs amortized to interest expense	333,000
Maximum [Member]
Line of Credit Facility [Line Items]
Unused line of credit commitment fees basis points	50
Minimum [Member]
Line of Credit Facility [Line Items]
Unused line of credit commitment fees basis points	40
Canadian Sublimit [Member]
Line of Credit Facility [Line Items]
Revolving credit facility amount		$ 25,000,000
ABR Loan [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Spread over LIBOR or prime rate	175
ABR Loan [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Spread over LIBOR or prime rate	125
Eurodollar/CDOR Loans [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Spread over LIBOR or prime rate	275
Eurodollar/CDOR Loans [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Spread over LIBOR or prime rate	225