Guarantor Financial Statements - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 367,134	$ 10,759	$ 162,128	$ 74,488
Accounts receivable	42,185	48,031
Fair value of derivative contracts	30,222	38,576
Current income tax receivable	46,174	46,174
Inventory	535	535
Other current assets	6,531	6,346
Total current assets	492,781	150,421
Oil and gas properties, full cost method:
Proved	9,481,859	9,375,898
Less: accumulated DD&A	(8,796,412)	(8,603,955)
Net proved oil and gas properties	685,447	771,943
Unevaluated	421,429	440,043
Other property and equipment, net	28,667	29,289
Other assets, net	18,257	18,473
Investment in subsidiary	0
Total assets	1,646,581	1,410,169
Current liabilities:
Accounts payable to vendors	38,200	82,207
Undistributed oil and gas proceeds	3,875	5,992
Accrued interest	22,901	9,022
Asset retirement obligations	23,465	21,291
Current portion of long-term debt	459,201	0
Other current liabilities	32,671	40,712
Total current liabilities	580,313	159,224
Long-term debt	1,063,090	1,060,955
Asset retirement obligations	209,848	204,575
Other long-term liabilities	18,329	25,204
Total liabilities	$ 1,871,580	$ 1,449,958
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 558	$ 553
Treasury stock	(860)	(860)
Additional paid-in capital	1,650,969	1,648,189
Accumulated deficit	(1,894,407)	(1,705,623)
Accumulated other comprehensive income (loss)	18,741	17,952	70,800	83,300
Total stockholders’ equity	(224,999)	(39,789)
Total liabilities and stockholders’ equity	1,646,581	1,410,169
Parent
Current assets:
Cash and cash equivalents	367,133	9,681	131,936	72,886
Accounts receivable	57,106	10,597
Fair value of derivative contracts	0
Current income tax receivable	46,174	46,174
Inventory	535	535
Other current assets	6,531	6,313
Total current assets	477,479	73,300
Oil and gas properties, full cost method:
Proved	1,891,423	1,875,152
Less: accumulated DD&A	(1,891,423)	(1,874,622)
Net proved oil and gas properties	0	530
Unevaluated	261,724	253,308
Other property and equipment, net	28,667	29,289
Other assets, net	17,460	16,612
Investment in subsidiary	614,540	745,033
Total assets	1,399,870	1,118,072
Current liabilities:
Accounts payable to vendors	24,915	16,063
Undistributed oil and gas proceeds	2,800	5,216
Accrued interest	22,901	9,022
Asset retirement obligations	0
Current portion of long-term debt	459,201
Other current liabilities	32,335	40,161
Total current liabilities	542,152	70,462
Long-term debt	1,063,090	1,060,955
Asset retirement obligations	1,298	1,240
Other long-term liabilities	18,329	25,204
Total liabilities	$ 1,624,869	$ 1,157,861
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 558	$ 553
Treasury stock	(860)	(860)
Additional paid-in capital	1,650,969	1,648,189
Accumulated deficit	(1,894,407)	(1,705,623)
Accumulated other comprehensive income (loss)	18,741	17,952
Total stockholders’ equity	(224,999)	(39,789)
Total liabilities and stockholders’ equity	1,399,870	1,118,072
Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	1	2	30,015	1,450
Accounts receivable	38,476	39,190
Fair value of derivative contracts	30,222	38,576
Current income tax receivable	0
Inventory	0	0
Other current assets	0
Total current assets	68,699	77,768
Oil and gas properties, full cost method:
Proved	7,544,791	7,458,262
Less: accumulated DD&A	(6,859,344)	(6,686,849)
Net proved oil and gas properties	685,447	771,413
Unevaluated	159,705	186,735
Other property and equipment, net	0
Other assets, net	797	826
Investment in subsidiary	0
Total assets	914,648	1,036,742
Current liabilities:
Accounts payable to vendors	67,567	67,901
Undistributed oil and gas proceeds	1,075	776
Accrued interest	0
Asset retirement obligations	23,465	20,400
Current portion of long-term debt	0
Other current liabilities	336	551
Total current liabilities	92,443	89,628
Long-term debt	0
Asset retirement obligations	208,550	203,335
Other long-term liabilities	0
Total liabilities	$ 300,993	$ 292,963
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 0
Treasury stock	0
Additional paid-in capital	1,344,577	$ 1,344,577
Accumulated deficit	(749,663)	(624,824)
Accumulated other comprehensive income (loss)	18,741	24,026
Total stockholders’ equity	613,655	743,779
Total liabilities and stockholders’ equity	914,648	1,036,742
Non- Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	0	1,076	177	152
Accounts receivable	885	0
Fair value of derivative contracts	0
Current income tax receivable	0
Inventory	0
Other current assets	0	33
Total current assets	885	1,109
Oil and gas properties, full cost method:
Proved	45,645	42,484
Less: accumulated DD&A	(45,645)	(42,484)
Net proved oil and gas properties	0
Unevaluated	0	0
Other property and equipment, net	0
Other assets, net	0	1,035
Investment in subsidiary	0	1,088
Total assets	885	3,232
Current liabilities:
Accounts payable to vendors	0
Undistributed oil and gas proceeds	0
Accrued interest	0
Asset retirement obligations	0	891
Current portion of long-term debt	0
Other current liabilities	0
Total current liabilities	0	891
Long-term debt	0
Asset retirement obligations	0
Other long-term liabilities	0
Total liabilities	$ 0	$ 891
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 0
Treasury stock	0
Additional paid-in capital	109,077	$ 109,795
Accumulated deficit	(108,192)	(95,306)
Accumulated other comprehensive income (loss)	0	(12,148)
Total stockholders’ equity	885	2,341
Total liabilities and stockholders’ equity	885	3,232
Eliminations
Current assets:
Cash and cash equivalents	0	0	$ 0	$ 0
Accounts receivable	(54,282)	(1,756)
Fair value of derivative contracts	0
Current income tax receivable	0
Inventory	0
Other current assets	0
Total current assets	(54,282)	(1,756)
Oil and gas properties, full cost method:
Proved	0
Less: accumulated DD&A	0
Net proved oil and gas properties	0
Unevaluated	0
Other property and equipment, net	0
Other assets, net	0
Investment in subsidiary	(614,540)	(746,121)
Total assets	(668,822)	(747,877)
Current liabilities:
Accounts payable to vendors	(54,282)	(1,757)
Undistributed oil and gas proceeds	0
Accrued interest	0
Asset retirement obligations	0
Current portion of long-term debt	0
Other current liabilities	0
Total current liabilities	(54,282)	(1,757)
Long-term debt	0
Asset retirement obligations	0
Other long-term liabilities	0
Total liabilities	$ (54,282)	$ (1,757)
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 0
Treasury stock	0
Additional paid-in capital	(1,453,654)	$ (1,454,372)
Accumulated deficit	857,855	720,130
Accumulated other comprehensive income (loss)	(18,741)	(11,878)
Total stockholders’ equity	(614,540)	(746,120)
Total liabilities and stockholders’ equity	$ (668,822)	$ (747,877)