ADDITIONAL BALANCE SHEET INFORMATION (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Accounts receivable, net
Trade accounts	$ 173,096	$ 165,070
Joint interest accounts	5,452	5,659
Other accounts	1,612	2,817
Accounts receivable, gross	180,160	173,546
Allowance for doubtful accounts	(1,681)	(1,127)
Accounts receivable, net	178,479	172,419
Inventories
Natural gas in storage	11,732	7,494
Tubular goods and well equipment	9,136	6,392
Other accounts	(29)	287
Inventory, net	20,839	14,173
Other current assets
Prepaid balances and other	3,703	2,158
Other assets current	3,703	2,158
Other assets
Deferred compensation plan	11,865	10,608
Debt issuance costs	14,652	17,420
Equity method investment	16,154	6,915
Other accounts	81	83
Other assets	42,752	35,026
Accounts payable
Trade accounts	24,295	5,097
Natural gas purchases	6,389	4,892
Royalty and other owners	75,896	66,321
Accrued capital costs	175,828	164,862
Taxes other than income	10,479	19,164
Drilling advances	35,686	44,203
Producer gas imbalances	1,381	1,602
Other accounts	5,395	6,339
Accounts payable current	335,349	312,480
Accrued liabilities
Employee benefits	32,870	16,011
Postretirement benefits	1,304	1,304
Taxes other than income	10,576	8,735
Interest payable	11,560	22,329
Other accounts	2,924	1,410
Accrued liabilities	59,234	49,789
Other liabilities
Deferred compensation plan	31,800	23,893
Other accounts	11,076	16,282
Other liabilities	$ 42,876	$ 40,175