Long-Term Debt And Other Long-Term Liabilities (Other Long-Term Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Long-term debt and other long-term liabilites [Abstract]
ARO liability	$ 69,444	$ 70,170	$ 98,297
Capital lease obligations	15,224	18,918
Workers' compensation	13,340	15,163
Separation benefit plans	6,524	4,943
Deferred compensation plan	5,390	4,578
Gas balancing liability	3,283	3,789
Other	0	410
Other liabilities	113,205	117,971
Less current portion	13,002	14,907
Total other long-term liabilities	$ 100,203	$ 103,064