Summary of Significant Accounting Policies (Details 6) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Self-insurance Program
Liabilities (undiscounted)	$ 46,178	$ 70,174
Discount rate	0.65%	1.01%
Amounts Recognized in Consolidated Balance Sheets
Other accrued liabilities	13,046	36,699
Other noncurrent liabilities	32,089	31,990
Accrued liabilities (discounted)	$ 45,135	$ 68,689