Long-Term Debt And Other Long-Term Liabilities (Long-Term Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current portion of long-term debt:
Unit credit agreement with an average interest rate of 4.0% at December 31, 2019	$ 108,200	$ 0
Long-term debt:
6.625% senior subordinated notes due 2021	650,000	650,000
Total principal amount	666,500	650,000
Less: unamortized discount	(971)	(1,623)
Less: debt issuance costs, net	(2,313)	(3,902)
Total long-term debt	663,216	644,475
Superior Credit Agreement [Member]
Long-term debt:
Superior credit agreement with an average interest rate of 3.9% at December 31, 2019	$ 16,500	$ 0
Line of Credit Facility, Interest Rate at Period End	3.90%	0.00%
Unit Credit Agreement [Member]
Current portion of long-term debt:
Unit credit agreement with an average interest rate of 4.0% at December 31, 2019	$ 108,200	$ 0
Long-term debt:
Line of Credit Facility, Interest Rate at Period End	4.00%	0.00%