Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets
Cash and cash equivalents	$ 13,463	$ 34,589
Accounts receivable, net	75,401	64,788
Inventories	14,785	8,641
Prepaid expenses	1,768	3,265
Derivative instruments	55,748	12,840
Total current assets	161,165	124,123
Property and equipment—at cost, net	75,853	65,711
Oil and natural gas properties, using the full cost method:
Proved	2,677,580	2,535,404
Unevaluated (excluded from the amortization base)	100,118	22,831
Accumulated depreciation, depletion, amortization and impairment	(1,203,858)	(1,135,567)
Total oil and natural gas properties	1,573,840	1,422,668
Derivative instruments	20,971	16,785
Deferred income taxes	982	7,526
Other assets	35,337	32,920
Total assets	1,868,148	1,669,733
Liabilities and stockholders' equity
Accounts payable and accrued liabilities	118,278	68,930
Accrued payroll and benefits payable	16,265	18,818
Accrued interest payable	23,811	30,882
Revenue distribution payable	17,072	20,800
Current maturities of long-term debt and capital leases	4,136	3,078
Derivative instruments	0	1,505
Deferred income taxes	34,873	23,704
Total current liabilities	214,435	167,717
Long-term debt, less current maturities	1,143,401	1,031,495
Derivative instruments	265	127
Stock-based compensation	2,201	2,788
Asset retirement obligations	44,767	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	421,912	419,370
Retained earnings (accumulated deficit)	3,028	(47,217)
Accumulated other comprehensive income, net of taxes	38,125	51,846
Total stockholders' equity	463,079	424,013
Total liabilities and stockholders' equity	1,868,148	1,669,733
Common Class A
Stockholders' equity:
Common stock	0	0
Common Class B
Stockholders' equity:
Common stock	4	4
Common Class C
Stockholders' equity:
Common stock	2	2
Common Class D
Stockholders' equity:
Common stock	3	3
Common Class E
Stockholders' equity:
Common stock	5	5
Common Class F
Stockholders' equity:
Common stock	0	0
Common Class G
Stockholders' equity:
Common stock	$ 0	$ 0