Unaudited Quarterly Consolidated Financial Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Consolidated Financial Information [Abstract]
Revenues	$ 224,992	$ 295,569	$ 330,942	$ 271,798	$ 203,713	$ 274,897	$ 295,585	$ 226,708	$ 1,123,301	$ 1,000,903	$ 789,695
Gross profit	106,350	160,743	196,085	144,799	99,811	147,175	170,218	119,206	607,977	536,410	423,764
Asset impairment	591		106	713	1	495		32	1,410	528	141
Income from operations	(4,897)	40,014	71,261	39,796	6,415	37,068	64,774	28,248	146,174	131,079	78,123
Net income	$ (3,607)	$ 45,080	$ 61,524	$ 28,346	$ 5,571	$ 30,207	$ 55,506	$ 21,504	$ 131,343	$ 112,788	$ 67,726
Basic income per common share	$ (0.04)	$ 0.50	$ 0.68	$ 0.32	$ 0.06	$ 0.34	$ 0.62	$ 0.24	$ 1.46	$ 1.27	$ 0.78
Diluted income per common share	$ (0.04)	$ 0.49	$ 0.68	$ 0.31	$ 0.06	$ 0.33	$ 0.61	$ 0.24	$ 1.44	$ 1.24	$ 0.76