Additional Balance Sheet Information (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Accounts receivable, net
Trade accounts	$ 117,971	$ 209,200
Other accounts	993	1,007
Accounts receivable, gross	118,964	210,207
Allowance for doubtful accounts	(1,046)	(1,184)
Accounts receivable, net	117,918	209,023
Other assets
Deferred compensation plan	18,537	18,381
Debt issuance costs	7,907	8,938
Operating lease right-of-use assets	34,948	35,916
Other accounts	52	56
Other assets	61,444	63,291
Accounts payable
Trade accounts	28,373	21,663
Royalty and other owners	23,442	36,191
Accrued transportation	48,115	55,586
Accrued capital costs	46,734	40,337
Taxes other than income	6,828	16,971
Other accounts	8,165	19,063
Accounts payable	161,657	189,811
Accrued liabilities
Employee benefits	16,455	22,727
Taxes other than income	3,255	3,850
Operating lease liabilities	3,665	3,124
Other accounts	1,520	1,589
Accrued liabilities	24,895	31,290
Other liabilities
Deferred compensation plan	27,055	27,012
Operating lease liabilities	31,182	32,677
Other accounts	9,806	8,595
Other liabilities	$ 68,043	$ 68,284
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssets	us-gaap:OtherAssets
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesCurrent	us-gaap:AccruedLiabilitiesCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent