Long-term Debt (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Long-term debt	$ 676,136
Less: current portion	57,168	103,690
Long-term debt, less current portion	569,026	475,174
Senior credit facilities
Debt Instrument [Line Items]
Long-term debt	493,345	370,589
Series A senior notes
Debt Instrument [Line Items]
Long-term debt	0	75,000
Series B senior notes
Debt Instrument [Line Items]
Long-term debt	100,000	100,000
Series C senior notes
Debt Instrument [Line Items]
Long-term debt	25,000	25,000
Other debt and capital leases
Debt Instrument [Line Items]
Long-term debt	$ 7,849	$ 8,275