Credit Facility (Details) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 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
Additional borrowings in credit facility		100,000,000
Amounts of outstanding	0	0
Interest on credit facility	100,000	200,000
Capitalized debt issuance costs		1,900,000
Capitalized debt issuance costs remaining		1,700,000
Debt issuance costs amortized to interest expense	100,000	200,000
Canadian Sublimit [Member]
Line of Credit Facility [Line Items]
Revolving credit facility amount			$ 25,000,000
Maximum [Member] | ABR Loan [Member]
Line of Credit Facility [Line Items]
Spread over LIBOR or prime rate	175	175
Minimum [Member] | ABR Loan [Member]
Line of Credit Facility [Line Items]
Spread over LIBOR or prime rate	125	125
Maximum [Member] | Eurodollar/CDOR Loans [Member]
Line of Credit Facility [Line Items]
Spread over LIBOR or prime rate	275	275
Minimum [Member] | Eurodollar/CDOR Loans [Member]
Line of Credit Facility [Line Items]
Spread over LIBOR or prime rate	225	225
Maximum [Member]
Line of Credit Facility [Line Items]
Unused Line of Credit Commitment Fees basis points		50
Leverage ratio		2.75
Interest coverage ratio		3.0
Minimum [Member]
Line of Credit Facility [Line Items]
Unused Line of Credit Commitment Fees basis points		40
Leverage ratio		1.00
Interest coverage ratio		1.0