Additional Balance Sheet Information (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accounts receivable, net
Trade accounts	$ 198,625	$ 215,301
Other accounts	257	462
Accounts receivable, gross	198,882	215,763
Allowance for doubtful accounts	(1,039)	(1,039)
Accounts receivable, net	197,843	214,724
Other assets
Deferred compensation plan	24,296	22,510
Debt issuance costs	6,360	6,875
Operating lease right-of-use assets	32,725	33,741
Other accounts	128	85
Other assets	63,509	63,211
Accounts payable
Trade accounts	17,230	12,896
Royalty and other owners	34,496	37,243
Accrued transportation	51,530	52,238
Accrued capital costs	38,280	37,872
Taxes other than income	18,420	13,736
Other accounts	9,145	8,096
Accounts payable	169,101	162,081
Accrued liabilities
Employee benefits	13,127	14,270
Taxes other than income	3,082	3,026
Operating lease liabilities	3,910	3,991
Other accounts	1,121	1,087
Accrued liabilities	21,240	22,374
Other liabilities
Deferred compensation plan	33,607	30,581
Operating lease liabilities	28,697	29,628
Other accounts	16,224	21,069
Other liabilities	$ 78,528	$ 81,278