Consolidated balance sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Assets
Cash and cash equivalents	$ 38,657	$ 48,595
Accounts receivable, net	116,387	96,515
Inventories, net	22,078	16,137
Prepaid expenses	3,268	3,998
Derivative instruments	0	2,152
Deferred income taxes	15,599	9,260
Total current assets	195,989	176,657
Property and equipment—at cost, net	69,775	69,426
Oil and natural gas properties, using the full cost method:
Proved	3,372,416	3,258,661
Unevaluated (excluded from the amortization base)	346,372	321,477
Accumulated depreciation, depletion, amortization and impairment	(1,522,249)	(1,470,090)
Total oil and natural gas properties	2,196,539	2,110,048
Derivative instruments	2,847	6,403
Other assets	34,285	35,348
Total assets	2,499,435	2,397,882
Liabilities and stockholders' equity
Accounts payable and accrued liabilities	157,911	134,811
Accrued payroll and benefits payable	19,196	24,246
Accrued interest payable	33,441	24,225
Revenue distribution payable	23,458	25,138
Current maturities of long-term debt and capital leases	5,502	5,334
Derivative instruments	22,830	8,234
Total current liabilities	262,338	221,988
Long-term debt and capital leases, less current maturities	1,603,532	1,557,528
Derivative instruments	140	0
Stock-based compensation	3,514	4,942
Asset retirement obligations, net of current portion	54,348	53,305
Deferred income taxes	71,680	62,855
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock, 600,000 shares authorized, none issued and outstanding	0	0
Additional paid in capital	426,591	424,377
Retained earnings	77,278	72,873
Total stockholders' equity	503,883	497,264
Total liabilities and stockholders' equity	2,499,435	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