Long-Term Debt (Details) (USD $)						0 Months Ended		3 Months Ended			3 Months Ended					3 Months Ended		3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 2012 notes - 7.625%	Dec. 31, 2012 2012 notes - 7.625%	Aug. 07, 2012 2012 notes - 7.625%	Feb. 12, 2013 Add-on notes - 7.625%	Mar. 31, 2013 Add-on notes - 7.625%	Mar. 31, 2013 Floating Rate Notes	Dec. 31, 2012 Floating Rate Notes	May 31, 2007 Floating Rate Notes	Mar. 31, 2013 Senior secured credit facility item	Dec. 31, 2012 Senior secured credit facility	May 06, 2010 Senior secured credit facility	Mar. 31, 2013 Senior secured credit facility Maximum	Mar. 31, 2013 Senior secured credit facility Minimum	Mar. 31, 2013 Senior secured credit facility Prime rate	Mar. 31, 2013 Senior secured credit facility Adjusted LIBOR	Mar. 31, 2013 Senior secured credit facility Federal funds rate	Mar. 31, 2013 Senior secured credit facility One month Eurodollar rate	Mar. 31, 2013 Senior secured credit facility Adjusted British Bankers Association Interest Settlement Rate Maximum	Mar. 31, 2013 Senior secured credit facility Adjusted British Bankers Association Interest Settlement Rate Minimum	Mar. 31, 2013 Capital lease obligations	Dec. 31, 2012 Capital lease obligations	Jul. 31, 2012 Second Amended and Restated Credit Agreement
Long-Term Debt
Unamortized bond premium	$ 13,828,000						$ 13,800,000
Long-term debt current and noncurrent	707,477,000	699,014,000	425,000,000	425,000,000			220,000,000		230,000,000		33,500,000	28,000,000										15,149,000	16,014,000
Less: Current portion of long-term debt	(5,959,000)	(6,223,000)
Total long-term debt	701,518,000	692,791,000
Interest rate (as a percent)			7.625%	7.625%	7.625%	7.625%	7.625%
Premium on issue of debt (as a percent)						106.375%
Aggregate total amount of proceeds						230,000,000
Aggregate outstanding principal amount					425,000,000	220,000,000				230,000,000
Ownership interest in existing and certain future owned domestic subsidiaries (as a percent)	100.00%
Base rate								LIBOR								prime rate		federal funds rate	Eurodollar rate
Margin over base rate (as a percent)								3.375%						1.50%	1.00%	4.75%	2.703%	0.50%	1.00%	2.50%	2.00%
Maximum borrowing capacity													195,000,000											235,000,000
Minimum available borrowing capacity required to be maintained for a certain period under financial covenants											20,000,000
Minimum ratio of EBITDA to cash expense, number of quarters											4
Borrowing outstanding											33,500,000					3,500,000	30,000,000
Available amount											167,700,000
Borrowing base											204,700,000
Letters of credit											$ 3,500,000