Guarantor Financial Statements - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 10,759	$ 74,488	$ 331,224	$ 279,526
Restricted cash	0	177,647
Accounts receivable	48,031	120,359
Fair value of derivative contracts	38,576	139,179
Current income tax receivable	46,174	7,212
Deferred taxes		0
Inventory	535	3,709
Other current assets	6,346	8,118
Total current assets	150,421	530,712
Oil and gas properties, full cost method:
Proved	9,375,898	8,817,268
Less: accumulated DD&A	(8,603,955)	(6,970,631)
Net proved oil and gas properties	771,943	1,846,637
Unevaluated	440,043	567,365
Other property and equipment, net	29,289	32,340
Fair value of derivative contracts	0	14,333
Other assets, net	18,473	18,470
Investment in subsidiary	0	0
Total assets	1,410,169	3,009,857
Current liabilities:
Accounts payable to vendors	82,207	132,629
Undistributed oil and gas proceeds	5,992	23,232
Accrued interest	9,022	9,022
Deferred taxes	0	20,119
Asset retirement obligations	21,291	69,400
Other current liabilities	40,712	49,505
Total current liabilities	159,224	303,907
Long-term debt	1,060,955	1,032,281
Deferred taxes	0	286,343
Asset retirement obligations	204,575	247,009
Other long-term liabilities	25,204	38,714
Total liabilities	$ 1,449,958	$ 1,908,254
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 553	$ 549
Treasury stock	(860)	(860)
Additional paid-in capital	1,648,189	1,633,307
Accumulated deficit	(1,705,623)	(614,708)
Accumulated other comprehensive income	17,952	83,315	(2,062)	28,833
Total stockholders’ equity	(39,789)	1,101,603
Total liabilities and stockholders’ equity	1,410,169	3,009,857
Parent [Member]
Current assets:
Cash and cash equivalents	9,681	72,886	246,294	228,398
Restricted cash		177,647
Accounts receivable	10,597	73,711
Fair value of derivative contracts	0	0
Current income tax receivable	46,174	7,212
Deferred taxes		4,095
Inventory	535	1,011
Other current assets	6,313	8,112
Total current assets	73,300	344,674
Oil and gas properties, full cost method:
Proved	1,875,152	1,689,802
Less: accumulated DD&A	(1,874,622)	(970,387)
Net proved oil and gas properties	530	719,415
Unevaluated	253,308	289,556
Other property and equipment, net	29,289	32,340
Fair value of derivative contracts		0
Other assets, net	16,612	12,103
Investment in subsidiary	745,033	1,050,546
Total assets	1,118,072	2,448,634
Current liabilities:
Accounts payable to vendors	16,063	74,756
Undistributed oil and gas proceeds	5,216	22,158
Accrued interest	9,022	9,022
Deferred taxes		0
Asset retirement obligations	0	0
Other current liabilities	40,161	49,306
Total current liabilities	70,462	155,242
Long-term debt	1,060,955	1,032,281
Deferred taxes		117,206
Asset retirement obligations	1,240	3,588
Other long-term liabilities	25,204	38,714
Total liabilities	$ 1,157,861	$ 1,347,031
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 553	$ 549
Treasury stock	(860)	(860)
Additional paid-in capital	1,648,189	1,633,307
Accumulated deficit	(1,705,623)	(614,708)
Accumulated other comprehensive income	17,952	83,315
Total stockholders’ equity	(39,789)	1,101,603
Total liabilities and stockholders’ equity	1,118,072	2,448,634
Guarantor Subsidiary [Member]
Current assets:
Cash and cash equivalents	2	1,450	84,290	51,128
Restricted cash		0
Accounts receivable	39,190	46,615
Fair value of derivative contracts	38,576	139,179
Current income tax receivable	0	0
Deferred taxes		0
Inventory	0	2,698
Other current assets	0	0
Total current assets	77,768	189,942
Oil and gas properties, full cost method:
Proved	7,458,262	7,127,466
Less: accumulated DD&A	(6,686,849)	(6,000,244)
Net proved oil and gas properties	771,413	1,127,222
Unevaluated	186,735	241,230
Other property and equipment, net	0	0
Fair value of derivative contracts		14,333
Other assets, net	826	1,360
Investment in subsidiary	0	0
Total assets	1,036,742	1,574,087
Current liabilities:
Accounts payable to vendors	67,901	57,873
Undistributed oil and gas proceeds	776	1,074
Accrued interest	0	0
Deferred taxes		24,214
Asset retirement obligations	20,400	69,400
Other current liabilities	551	199
Total current liabilities	89,628	152,760
Long-term debt	0	0
Deferred taxes		169,137
Asset retirement obligations	203,335	243,421
Other long-term liabilities	0	0
Total liabilities	$ 292,963	$ 565,318
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 0	$ 0
Treasury stock	0	0
Additional paid-in capital	1,344,577	1,362,684
Accumulated deficit	(624,824)	(440,699)
Accumulated other comprehensive income	24,026	86,784
Total stockholders’ equity	743,779	1,008,769
Total liabilities and stockholders’ equity	1,036,742	1,574,087
Non-Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	1,076	152	640	0
Restricted cash		0
Accounts receivable	0	33
Fair value of derivative contracts	0	0
Current income tax receivable	0	0
Deferred taxes		0
Inventory	0	0
Other current assets	33	6
Total current assets	1,109	191
Oil and gas properties, full cost method:
Proved	42,484	0
Less: accumulated DD&A	(42,484)	0
Net proved oil and gas properties	0	0
Unevaluated	0	36,579
Other property and equipment, net	0	0
Fair value of derivative contracts		0
Other assets, net	1,035	5,007
Investment in subsidiary	1,088	41,638
Total assets	3,232	83,415
Current liabilities:
Accounts payable to vendors	0	0
Undistributed oil and gas proceeds	0	0
Accrued interest	0	0
Deferred taxes		0
Asset retirement obligations	891	0
Other current liabilities	0	0
Total current liabilities	891	0
Long-term debt	0	0
Deferred taxes		0
Asset retirement obligations	0	0
Other long-term liabilities	0	0
Total liabilities	$ 891	$ 0
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 0	$ 0
Treasury stock	0	0
Additional paid-in capital	109,795	90,339
Accumulated deficit	(95,306)	12
Accumulated other comprehensive income	(12,148)	(6,936)
Total stockholders’ equity	2,341	83,415
Total liabilities and stockholders’ equity	3,232	83,415
Eliminations [Member]
Current assets:
Cash and cash equivalents	0	0	$ 0	$ 0
Restricted cash		0
Accounts receivable	(1,756)	0
Fair value of derivative contracts	0	0
Current income tax receivable	0	0
Deferred taxes		(4,095)
Inventory	0	0
Other current assets	0	0
Total current assets	(1,756)	(4,095)
Oil and gas properties, full cost method:
Proved	0	0
Less: accumulated DD&A	0	0
Net proved oil and gas properties	0	0
Unevaluated	0	0
Other property and equipment, net	0	0
Fair value of derivative contracts		0
Other assets, net	0	0
Investment in subsidiary	(746,121)	(1,092,184)
Total assets	(747,877)	(1,096,279)
Current liabilities:
Accounts payable to vendors	(1,757)	0
Undistributed oil and gas proceeds	0	0
Accrued interest	0	0
Deferred taxes		(4,095)
Asset retirement obligations	0	0
Other current liabilities	0	0
Total current liabilities	(1,757)	(4,095)
Long-term debt	0	0
Deferred taxes		0
Asset retirement obligations	0	0
Other long-term liabilities	0	0
Total liabilities	$ (1,757)	$ (4,095)
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 0	$ 0
Treasury stock	0	0
Additional paid-in capital	(1,454,372)	(1,453,023)
Accumulated deficit	720,130	440,687
Accumulated other comprehensive income	(11,878)	(79,848)
Total stockholders’ equity	(746,120)	(1,092,184)
Total liabilities and stockholders’ equity	$ (747,877)	$ (1,096,279)