Long-Term Debt And Other Long-Term Liabilities (Other Long-Term Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Asset retirement obligation (ARO) liability	$ 64,072	$ 64,208	$ 62,727	$ 69,444
Workers' compensation	12,090	12,738
Finance lease obligations	8,395	11,380
Contract liability	7,787	9,881
Separation benefit plans	10,028	8,814
Deferred compensation plan	6,017	5,132
Gas balancing liability	3,373	3,331
Other liabilities	111,762	115,484
Current portion of other long-term liabilities	15,402	14,250
Other long-term liabilities	$ 96,360	$ 101,234