Additional Balance Sheet Information (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounts receivable, net
Trade accounts	$ 136,740	$ 209,200
Other accounts	1,037	1,007
Accounts receivable, gross	137,777	210,207
Allowance for doubtful accounts	(1,039)	(1,184)
Accounts receivable, net	136,738	209,023
Other assets
Deferred compensation plan	19,882	18,381
Debt issuance costs	7,391	8,938
Operating lease right-of-use assets	34,721	35,916
Other accounts	79	56
Other assets	62,073	63,291
Accounts payable
Trade accounts	20,789	21,663
Royalty and other owners	25,836	36,191
Accrued transportation	50,999	55,586
Accrued capital costs	27,850	40,337
Taxes other than income	10,262	16,971
Other accounts	15,926	19,063
Accounts payable	151,662	189,811
Accrued liabilities
Employee benefits	19,822	22,727
Taxes other than income	3,243	3,850
Operating lease liabilities	4,027	3,124
Other accounts	1,304	1,589
Accrued liabilities	28,396	31,290
Other liabilities
Deferred compensation plan	28,489	27,012
Derivative instruments	4,095	0
Operating lease liabilities	30,594	32,677
Other accounts	12,091	8,595
Other liabilities	$ 75,269	$ 68,284