Long-Term Debt And Other Long-Term Liabilities (Other Long-Term Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Asset retirement obligation (ARO) liability	$ 67,433	$ 64,208	$ 62,838	$ 69,444
Workers' compensation	12,118	12,738
Finance lease obligations	9,400	11,380
Contract liability	8,513	9,881
Separation benefit plans	9,749	8,814
Deferred compensation plan	6,002	5,132
Gas balancing liability	3,372	3,331
Other liabilities	116,587	115,484
Current portion of other long-term liabilities	13,887	14,250
Other long-term liabilities	$ 102,700	$ 101,234