Long-Term Debt And Other Long-Term Liabilities (Other Long-Term Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Debt Disclosure [Abstract]
Asset retirement obligation (ARO) liability	$ 70,759	$ 98,297	$ 95,441	$ 100,567
Capital lease obligations	21,592	22,466
Workers' compensation	16,735	16,551
Separation benefit plans	8,301	9,886
Deferred compensation plan	4,381	4,244
Gas balancing liability	3,805	5,047
Other	410	410
Other liabilities	125,983	156,901
Less current portion	19,053	16,560
Total other long-term liabilities	$ 106,930	$ 140,341