Long-Term Debt And Other Long-Term Liabilities (Other Long-Term Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Asset retirement obligation (ARO) liability	$ 75,485	$ 70,170	$ 71,021	$ 98,297
Capital lease obligations	16,161	18,918
Workers' compensation	13,420	15,163
Separation benefit plans	6,020	4,943
Deferred compensation plan	5,287	4,578
Gas balancing liability	3,322	3,789
Other	0	410
Other liabilities	119,695	117,971
Less current portion	14,227	14,907
Total other long-term liabilities	$ 105,468	$ 103,064