Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets
Cash and cash equivalents	$ 32,026	$ 29,819
Accounts receivable, net	91,179	77,307
Inventories, net	14,532	10,510
Prepaid expenses	1,861	3,465
Derivative instruments	25,617	42,516
Total current assets	165,215	163,617
Property and equipment—at cost, net	66,969	65,601
Oil and natural gas properties, using the full cost method:
Proved	3,001,518	2,860,611
Unevaluated (excluded from the amortization base)	215,172	162,921
Accumulated depreciation, depletion, amortization and impairment	(1,375,932)	(1,290,356)
Total oil and natural gas properties	1,840,758	1,733,176
Derivative instruments	17,193	517
Assets held for sale	5,689	5,689
Other assets	36,999	38,952
Total assets	2,132,823	2,007,552
Liabilities and stockholders' equity
Accounts payable and accrued liabilities	120,966	101,598
Accrued payroll and benefits payable	17,409	19,655
Accrued interest payable	24,146	24,131
Revenue distribution payable	22,175	18,152
Current maturities of long-term debt	2,805	3,746
Derivative instruments	266	436
Deferred income taxes	13,494	26,872
Total current liabilities	201,261	194,590
Long-term debt, less current maturities	1,357,417	1,289,656
Derivative instruments	47	2,192
Stock-based compensation	2,039	3,042
Asset retirement obligations, net of current portion	45,717	46,314
Deferred income taxes	36,826	8,901
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock, 600,000 shares authorized, none issued and outstanding	0	0
Additional paid in capital	423,435	422,434
Retained earnings	54,896	17,186
Accumulated other comprehensive income, net of taxes	11,171	23,223
Total stockholders' equity	489,516	462,857
Total liabilities and stockholders' equity	2,132,823	2,007,552
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