Long-Term Debt And Other Long-Term Liabilities (Other Long-Term Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Asset retirement obligation (ARO) liability	$ 70,049	$ 70,170	$ 70,926	$ 98,297
Capital lease obligations	17,089	18,918
Workers' compensation	13,971	15,163
Separation benefit plans	5,456	4,943
Deferred compensation plan	5,092	4,578
Gas balancing liability	3,322	3,789
Other	410	410
Other liabilities	115,389	117,971
Less current portion	14,593	14,907
Total other long-term liabilities	$ 100,796	$ 103,064