Guarantor Financial Statements - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 169,194		$ 10,759	$ 141,655		$ 74,488
Accounts receivable	38,276		48,031
Fair value of derivative contracts	11,887		38,576
Current income tax receivable	46,174		46,174
Other current assets	12,080		6,881
Total current assets	277,611		150,421
Oil and gas properties, full cost method:
Proved	9,518,245		9,375,898
Less: accumulated DD&A	(8,960,440)		(8,603,955)
Net proved oil and gas properties	557,805		771,943
Unevaluated	425,204		440,043
Other property and equipment, net	27,968		29,289
Other assets, net	28,183		18,473
Investment in subsidiary	0
Total assets	1,316,771		1,410,169
Current liabilities:
Accounts payable to vendors	28,914		82,207
Undistributed oil and gas proceeds	5,071		5,992
Accrued interest	9,773		9,022
Fair value of derivative contracts	37		0
Asset retirement obligations	33,695		21,291
Current portion of long-term debt	288,336		0
Other current liabilities	34,793		40,712
Total current liabilities	400,619		159,224
Long-term debt	1,122,901		1,060,955
Asset retirement obligations	203,661		204,575
Other long-term liabilities	18,446		25,204
Total liabilities	1,745,627		1,449,958
Commitments and contingencies
Stockholders’ equity:
Common stock	56		55
Treasury stock	(860)		(860)
Additional paid-in capital	1,654,731		1,648,687
Accumulated deficit	(2,090,168)		(1,705,623)
Accumulated other comprehensive income (loss)	7,385	$ 18,700	17,952	40,700	$ 70,800	83,300
Total stockholders’ equity	(428,856)		(39,789)
Total liabilities and stockholders’ equity	1,316,771		1,410,169
Parent
Current assets:
Cash and cash equivalents	169,193		9,681	116,427		72,886
Accounts receivable	25,410		10,597
Fair value of derivative contracts	0
Current income tax receivable	46,174		46,174
Other current assets	12,080		6,848
Total current assets	252,857		73,300
Oil and gas properties, full cost method:
Proved	1,907,347		1,875,152
Less: accumulated DD&A	(1,907,326)		(1,874,622)
Net proved oil and gas properties	21		530
Unevaluated	261,971		253,308
Other property and equipment, net	27,968		29,289
Other assets, net	27,445		16,612
Investment in subsidiary	503,738		745,033
Total assets	1,074,000		1,118,072
Current liabilities:
Accounts payable to vendors	23,153		16,063
Undistributed oil and gas proceeds	4,379		5,216
Accrued interest	9,773		9,022
Fair value of derivative contracts	0
Asset retirement obligations	0
Current portion of long-term debt	288,336
Other current liabilities	34,513		40,161
Total current liabilities	360,154		70,462
Long-term debt	1,122,901		1,060,955
Asset retirement obligations	1,355		1,240
Other long-term liabilities	18,446		25,204
Total liabilities	1,502,856		1,157,861
Commitments and contingencies
Stockholders’ equity:
Common stock	56		55
Treasury stock	(860)		(860)
Additional paid-in capital	1,654,731		1,648,687
Accumulated deficit	(2,090,168)		(1,705,623)
Accumulated other comprehensive income (loss)	7,385		17,952
Total stockholders’ equity	(428,856)		(39,789)
Total liabilities and stockholders’ equity	1,074,000		1,118,072
Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	1		2	25,034		1,450
Accounts receivable	31,171		39,190
Fair value of derivative contracts	11,887		38,576
Current income tax receivable	0
Other current assets	0
Total current assets	43,059		77,768
Oil and gas properties, full cost method:
Proved	7,565,003		7,458,262
Less: accumulated DD&A	(7,007,219)		(6,686,849)
Net proved oil and gas properties	557,784		771,413
Unevaluated	163,233		186,735
Other property and equipment, net	0
Other assets, net	738		826
Investment in subsidiary	0
Total assets	764,814		1,036,742
Current liabilities:
Accounts payable to vendors	24,950		67,901
Undistributed oil and gas proceeds	692		776
Accrued interest	0
Fair value of derivative contracts	37
Asset retirement obligations	33,695		20,400
Current portion of long-term debt	0
Other current liabilities	280		551
Total current liabilities	59,654		89,628
Long-term debt	0
Asset retirement obligations	202,306		203,335
Other long-term liabilities
Total liabilities	261,960		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	(849,108)		(624,824)
Accumulated other comprehensive income (loss)	7,385		24,026
Total stockholders’ equity	502,854		743,779
Total liabilities and stockholders’ equity	764,814		1,036,742
Non- Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	0		1,076	194		152
Accounts receivable	883		0
Fair value of derivative contracts	0
Current income tax receivable	0
Other current assets	0		33
Total current assets	883		1,109
Oil and gas properties, full cost method:
Proved	45,895		42,484
Less: accumulated DD&A	(45,895)		(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	883		3,232
Current liabilities:
Accounts payable to vendors	0
Undistributed oil and gas proceeds	0
Accrued interest	0
Fair value of derivative contracts	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	109,078		109,795
Accumulated deficit	(108,195)		(95,306)
Accumulated other comprehensive income (loss)	0		(12,148)
Total stockholders’ equity	883		2,341
Total liabilities and stockholders’ equity	883		3,232
Eliminations
Current assets:
Cash and cash equivalents	0		0	$ 0		$ 0
Accounts receivable	(19,188)		(1,756)
Fair value of derivative contracts	0
Current income tax receivable	0
Other current assets	0
Total current assets	(19,188)		(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	(503,738)		(746,121)
Total assets	(522,926)		(747,877)
Current liabilities:
Accounts payable to vendors	(19,189)		(1,757)
Undistributed oil and gas proceeds	0
Accrued interest	0
Fair value of derivative contracts	0
Asset retirement obligations	0
Current portion of long-term debt	0
Other current liabilities	0
Total current liabilities	(19,189)		(1,757)
Long-term debt	0
Asset retirement obligations	0
Other long-term liabilities	0
Total liabilities	(19,189)		(1,757)
Commitments and contingencies
Stockholders’ equity:
Common stock	0
Treasury stock	0
Additional paid-in capital	(1,453,655)		(1,454,372)
Accumulated deficit	957,303		720,130
Accumulated other comprehensive income (loss)	(7,385)		(11,878)
Total stockholders’ equity	(503,737)		(746,120)
Total liabilities and stockholders’ equity	$ (522,926)		$ (747,877)