Additional Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accounts receivable, net
Trade accounts	$ 227,835	$ 215,361
Joint interest accounts	2,245	7,261
Income taxes receivable	3,612	922
Other accounts	6,515	746
Accounts receivable, gross	240,207	224,290
Allowance for doubtful accounts	(1,198)	(1,814)
Accounts receivable, net	239,009	222,476
Inventories
Natural gas in storage	3,281	9,056
Tubular goods and well equipment	10,675	8,396
Other accounts	70	16
Other current assets
Prepaid balances and other	1,855	2,587
Other assets current	1,855	2,587
Other assets
Deferred compensation plan	13,115	12,507
Debt issuance cost	17,349	16,476
Other accounts	65	79
Other assets	30,529	29,062
Accounts payable
Trade accounts	54,949	26,023
Natural gas purchases	2,407	2,052
Royalty and other owners	97,298	79,150
Accrued capital costs	222,426	146,899
Taxes other than income	16,806	13,677
Drilling advances	88	14,093
Other accounts	6,102	6,907
Accounts payable current	400,076	288,801
Accrued liabilities
Employee benefits	22,815	43,599
Taxes other than income	7,128	6,894
Interest payable	30,677	20,211
Other accounts	3,049	2,897
Accrued liabilities	63,669	73,601
Other liabilities
Deferred compensation plan	28,932	33,211
Other accounts	10,675	13,043
Other liabilities	$ 39,607	$ 46,254