Components of Selected Balance Sheet Accounts (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Other current assets:
Tubular inventory and well materials	$ 2,879	$ 4,033
Prepaid expenses	1,082	562
Prepaid Expense and Other Assets, Current, Total	3,961	4,595
Other assets:
Debt issuance costs	12,613	13,186
Assets of supplemental employee retirement plan (“SERP”)	3,401	3,237
Other	1,278	1,511
Other assets	17,292	17,934
Accounts payable and accrued liabilities:
Trade accounts payable	31,335	37,835
Drilling costs	43,858	37,703
Royalties	13,559	14,390
Production and franchise taxes	4,820	2,874
Compensation - related	2,713	6,853
Interest	19,072	5,828
Preferred stock dividends	1,725	1,687
Other	4,885	4,485
Accounts payable and accrued liabilities	121,967	111,655
Other liabilities:
Firm transportation obligation	13,870	14,333
Asset retirement obligations (“AROs”)	4,551	4,513
Defined benefit pension obligations	1,786	1,821
Postretirement health care benefit obligations	2,699	2,634
Deferred compensation - SERP obligation and other	3,469	3,310
Other	2,143	2,290
Other liabilities	$ 28,518	$ 28,901