Fair Value of Financial Instruments (Details 2) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	$ 564,921	$ 578,864
Fair Value	569,575	581,868
Series A Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	75,000	75,000
Fair Value	75,703	76,491
Series B Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	100,000	100,000
Fair Value	106,051	105,041
Series C Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	25,000	25,000
Fair Value	24,603	24,421
Revolving Credit Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	152,213	153,600
Fair Value	152,372	152,974
United States Term Loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	180,000	192,000
Fair Value	178,376	189,972
Canadian Term Loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	24,259	24,989
Fair Value	23,951	24,651
Other Debt Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	8,449	8,275
Fair Value	$ 8,519	$ 8,318