Additional Balance Sheet Information - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts receivable, net
Trade accounts	$ 215,511	$ 185,594
Joint interest accounts	467	1,359
Other accounts	1,312	5,335
Receivables gross current	217,290	192,288
Allowance for doubtful accounts	(1,286)	(1,243)
Accounts receivable, net	216,004	191,045
Inventories
Tubular goods and well equipment	8,006	11,005
Natural gas in storage	0	2,299
Inventory, net	8,006	13,304
Other assets
Deferred compensation plan	14,966	12,587
Debt issuance cost	7,990	11,403
Derivative instruments	2,239	2,991
Other accounts	56	58
Other assets	25,251	27,039
Accounts payable
Trade accounts	7,815	27,355
Natural gas purchases	4,299	2,231
Royalty and other owners	39,207	36,472
Accrued transportation	51,433	48,977
Accrued capital costs	31,130	34,647
Taxes other than income	16,801	13,827
Deposits received for asset sales	81,500	0
Other accounts	5,860	4,902
Accounts payable current	238,045	168,411
Accrued liabilities
Employee benefits	20,645	14,153
Taxes other than income	550	3,829
Asset retirement obligations	4,952	2,000
Other accounts	1,294	1,510
Accrued liabilities	27,441	21,492
Other liabilities
Deferred compensation plan	29,145	24,169
Other accounts	10,578	4,952
Other liabilities	$ 39,723	$ 29,121