Consolidated balance sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets
Cash and cash equivalents	$ 35,450	$ 48,595
Accounts receivable, net	113,365	96,515
Inventories, net	21,429	16,137
Prepaid expenses	2,591	3,998
Derivative instruments	0	2,152
Deferred income taxes	26,467	9,260
Total current assets	199,302	176,657
Property and equipment—at cost, net	68,927	69,426
Oil and natural gas properties, using the full cost method:
Proved	3,413,684	3,258,661
Unevaluated (excluded from the amortization base)	344,541	321,477
Accumulated depreciation, depletion, amortization and impairment	(1,582,078)	(1,470,090)
Total oil and natural gas properties	2,176,147	2,110,048
Derivative instruments	303	6,403
Other assets	33,031	35,348
Total assets	2,477,710	2,397,882
Liabilities and stockholders' equity
Accounts payable and accrued liabilities	168,968	134,811
Accrued payroll and benefits payable	21,382	24,246
Accrued interest payable	24,064	24,225
Revenue distribution payable	36,370	25,138
Current maturities of long-term debt and capital leases	5,623	5,334
Derivative instruments	46,818	8,234
Total current liabilities	303,225	221,988
Long-term debt and capital leases, less current maturities	1,532,544	1,557,528
Derivative instruments	17,157	0
Stock-based compensation	4,030	4,942
Asset retirement obligations and other	46,199	53,305
Deferred income taxes	77,357	62,855
Commitments and contingencies (Note 11)
Stockholders' equity:
Preferred stock, 600,000 shares authorized, none issued and outstanding	0	0
Additional paid in capital	428,339	424,377
Retained earnings	68,845	72,873
Total stockholders' equity	497,198	497,264
Total liabilities and stockholders' equity	2,477,710	2,397,882
Common Class A
Stockholders' equity:
Common stock	4	0
Common Class B
Stockholders' equity:
Common stock	3	4
Common Class C
Stockholders' equity:
Common stock	2	2
Common Class D
Stockholders' equity:
Common stock	0	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