Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets
Cash and cash equivalents	$ 22,501	$ 34,589
Accounts receivable, net	68,957	64,788
Inventories	13,008	8,641
Prepaid expenses	2,326	3,265
Derivative instruments	10,844	12,840
Total current assets	117,636	124,123
Property and equipment—at cost, net	74,922	65,711
Oil and natural gas properties, using the full cost method:
Proved	2,625,128	2,535,404
Unevaluated (excluded from the amortization base)	34,173	22,831
Accumulated depreciation, depletion, amortization and impairment	(1,169,112)	(1,135,567)
Total oil and natural gas properties	1,490,189	1,422,668
Derivative instruments	8,795	16,785
Deferred income taxes	3,103	7,526
Other assets	31,801	32,920
Total assets	1,726,446	1,669,733
Liabilities and stockholders' equity
Accounts payable and accrued liabilities	96,096	68,930
Accrued payroll and benefits payable	14,123	18,818
Accrued interest payable	22,825	30,882
Revenue distribution payable	18,008	20,800
Current maturities of long-term debt and capital leases	4,096	3,078
Derivative instruments	2,973	1,505
Deferred income taxes	20,697	23,704
Total current liabilities	178,818	167,717
Long-term debt and capital leases, less current maturities	1,071,955	1,031,495
Derivative instruments	1,393	127
Stock-based compensation	3,144	2,788
Asset retirement obligations	44,333	43,593
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock, 600,000 shares authorized, none issued and outstanding	0	0
Additional paid in capital	420,057	419,370
Accumulated deficit	(37,435)	(47,217)
Accumulated other comprehensive income, net of taxes	44,167	51,846
Total stockholders' equity	426,803	424,013
Total liabilities and stockholders' equity	1,726,446	1,669,733
Common Class A [Member]
Stockholders' equity:
Common stock	0	0
Common Class B [Member]
Stockholders' equity:
Common stock	4	4
Common Class C [Member]
Stockholders' equity:
Common stock	2	2
Common Class D [Member]
Stockholders' equity:
Common stock	3	3
Common Class E [Member]
Stockholders' equity:
Common stock	5	5
Common Class F [Member]
Stockholders' equity:
Common stock	0	0
Common Class G [Member]
Stockholders' equity:
Common stock	$ 0	$ 0