Additional Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Accounts receivable, net
Trade accounts	$ 215,361	$ 165,070
Joint interest accounts	7,261	5,659
Income taxes receivable	922
Other accounts	746	2,817
Accounts receivable, gross	224,290	173,546
Allowance for doubtful accounts	(1,814)	(1,127)
Accounts receivable, net	222,476	172,419
Inventories
Natural gas in storage	9,056	7,494
Tubular goods and well equipment	8,396	6,392
Other accounts	16	287
Inventory, net	17,468	14,173
Other current assets
Prepaid balances and other	2,587	2,158
Other assets current	2,587	2,158
Other assets
Deferred compensation plan	12,507	10,608
Debt issuance costs	16,476	17,420
Equity method investment	26,892	6,915
Other accounts	79	83
Other assets	55,954	35,026
Accounts payable
Trade accounts	26,023	14,037
Natural gas purchases	2,052	4,892
Royalty and other owners	79,150	66,321
Accrued capital costs	146,899	164,862
Taxes other than income	13,677	10,224
Drilling advances	14,093	44,203
Producer gas imbalances	69	1,602
Other accounts	6,838	6,339
Accounts payable current	288,801	312,480
Accrued liabilities
Employee benefits	43,599	17,315
Taxes other than income	6,894	8,735
Interest payable	20,211	22,329
Other accounts	2,897	1,218
Accrued liabilities	73,601	49,597
Other liabilities
Deferred compensation plan	33,211	23,893
Other accounts	13,043	16,282
Other liabilities	$ 46,254	$ 40,175