Leases (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating Leased Assets [Line Items]
Rental expense	$ 43,900,000	$ 41,600,000	$ 43,300,000
Royalty expense	349,000,000	286,800,000	230,500,000
Surety bonds outstanding	263,000,000
Secured lease obligation outstanding	263,000,000
Operating Lease [Member]
Operating Leased Assets [Line Items]
2011	28,903,000
2012	27,610,000
2013	25,119,000
2014	17,641,000
2015	9,648,000
Thereafter	12,640,000
Total	121,561,000
Leases [Member]
Operating Leased Assets [Line Items]
Surety bonds outstanding	64,600,000
Secured lease obligation outstanding	64,600,000
Royalty Agreements [Member] | Royalties [Member]
Operating Leased Assets [Line Items]
2011	24,378,000
2012	25,595,000
2013	25,810,000
2014	27,565,000
2015	24,397,000
Thereafter	114,371,000
Total	$ 242,116,000