Additional Balance Sheet Information (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accounts receivable, net
Trade accounts	$ 183,174	$ 215,301
Other accounts	565	462
Accounts receivable, gross	183,739	215,763
Allowance for doubtful accounts	(1,039)	(1,039)
Accounts receivable, net	182,700	214,724
Other assets
Deferred compensation plan	25,820	22,510
Debt issuance costs	5,844	6,875
Operating lease right-of-use assets	32,002	33,741
Other accounts	44	85
Other assets	63,710	63,211
Accounts payable
Trade accounts	18,595	12,896
Royalty and other owners	28,206	37,243
Accrued transportation	47,898	52,238
Accrued capital costs	52,994	37,872
Taxes other than income	8,805	13,736
Other accounts	9,758	8,096
Accounts payable	166,256	162,081
Accrued liabilities
Employee benefits	11,882	14,270
Taxes other than income	2,965	3,026
Operating lease liabilities	3,951	3,991
Other accounts	1,282	1,087
Accrued liabilities	20,080	22,374
Other liabilities
Deferred compensation plan	34,477	30,581
Operating lease liabilities	27,935	29,628
Other accounts	13,509	21,069
Other liabilities	$ 75,921	$ 81,278