Accrued Workers' Compensation (Schedule Of Amounts Recognized In Balance Sheet) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Accrued Workers Compensation [Line Items]
Less amount included in accrued expenses	$ 11,666,000	$ 6,659,000
Noncurrent obligations	71,948,000	35,290,000
Workers' Compensation [Member]
Accrued Workers Compensation [Line Items]
Occupational disease costs	29,430,000	24,537,000
Total obligations	83,614,000	41,949,000
Less amount included in accrued expenses	11,666,000	6,659,000
Noncurrent obligations	71,948,000	35,290,000
Surety bonds and letters of credit outstanding	60,100,000
Occupational Disease [Member]
Accrued Workers Compensation [Line Items]
Occupational disease costs	$ 54,184,000	$ 17,412,000