Guarantor Financial Statements - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Thousands		Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents		$ 141,655		$ 74,488	$ 333,886		$ 331,224
Restricted cash				177,647
Accounts receivable		68,706		120,359
Fair value of derivative contracts		74,319		139,179
Current income tax receivable		6		7,212
Inventory		3,709		3,709
Other current assets		10,076		8,118
Total current assets		298,471		530,712
Oil and gas properties, full cost method:
Proved		9,074,425		8,817,268
Less: accumulated DD&A		(7,846,343)		(6,970,631)
Net proved oil and gas properties		1,228,082		1,846,637
Unevaluated		529,589		567,365
Other property and equipment, net		30,736		32,340
Fair value of derivative contracts		8,231		14,333
Other assets, net		28,082		27,224
Total assets		2,123,191		3,018,611
Current liabilities:
Accounts payable to vendors		69,423		132,629
Undistributed oil and gas proceeds		17,000		23,232
Accrued interest		9,027		9,022
Deferred taxes	[1]	7,065		20,119
Asset retirement obligations		56,176		69,400
Other current liabilities		46,780		49,505
Total current liabilities		205,471		303,907
Long-term debt		1,048,406		1,041,035
Deferred taxes	[1]	11,752		286,343
Asset retirement obligations		240,613		247,009
Other long-term liabilities		32,213		38,714
Total liabilities		$ 1,538,455		$ 1,917,008
Commitments and contingencies
Stockholders' equity:
Common stock		$ 553		$ 549
Treasury stock		(860)		(860)
Additional paid-in capital		1,639,389		1,633,307
Accumulated deficit		(1,095,002)		(614,708)
Accumulated other comprehensive income (loss)		40,656	$ 70,800	83,315	(18,200)	$ (9,200)	(2,100)
Total stockholders' equity		584,736		1,101,603
Total liabilities and stockholders' equity		2,123,191		3,018,611
Parent [Member]
Current assets:
Cash and cash equivalents		116,427		72,886	244,254		246,294
Restricted cash				177,647
Accounts receivable		38,735		73,711
Current income tax receivable		6		7,212
Deferred taxes	[1]			4,095
Inventory		3,426		1,011
Other current assets		10,007		8,112
Total current assets		168,601		344,674
Oil and gas properties, full cost method:
Proved		1,778,480		1,689,802
Less: accumulated DD&A		(1,724,404)		(970,387)
Net proved oil and gas properties		54,076		719,415
Unevaluated		300,360		289,556
Other property and equipment, net		30,736		32,340
Other assets, net		25,149		20,857
Investment in subsidiary		1,057,810		1,050,546
Total assets		1,636,732		2,457,388
Current liabilities:
Accounts payable to vendors		56,763		74,756
Undistributed oil and gas proceeds		16,093		22,158
Accrued interest		9,027		9,022
Deferred taxes	[1]	298
Other current liabilities		46,724		49,306
Total current liabilities		128,905		155,242
Long-term debt		1,048,406		1,041,035
Deferred taxes	[1]	(161,285)		117,206
Asset retirement obligations		3,757		3,588
Other long-term liabilities		32,213		38,714
Total liabilities		$ 1,051,996		$ 1,355,785
Commitments and contingencies
Stockholders' equity:
Common stock		$ 553		$ 549
Treasury stock		(860)		(860)
Additional paid-in capital		1,639,389		1,633,307
Accumulated deficit		(1,095,002)		(614,708)
Accumulated other comprehensive income (loss)		40,656		83,315
Total stockholders' equity		584,736		1,101,603
Total liabilities and stockholders' equity		1,636,732		2,457,388
Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents		25,034		1,450	89,388		84,290
Accounts receivable		243,846		46,615
Fair value of derivative contracts		74,319		139,179
Inventory		283		2,698
Total current assets		343,482		189,942
Oil and gas properties, full cost method:
Proved		7,251,498		7,127,466
Less: accumulated DD&A		(6,077,492)		(6,000,244)
Net proved oil and gas properties		1,174,006		1,127,222
Unevaluated		227,067		241,230
Fair value of derivative contracts		8,231		14,333
Other assets, net		1,385		1,360
Total assets		1,754,171		1,574,087
Current liabilities:
Accounts payable to vendors		216,834		57,873
Undistributed oil and gas proceeds		907		1,074
Deferred taxes	[1]	6,767		24,214
Asset retirement obligations		56,176		69,400
Other current liabilities		56		199
Total current liabilities		280,740		152,760
Deferred taxes	[1]	189,303		169,137
Asset retirement obligations		236,856		243,421
Total liabilities		$ 706,899		$ 565,318
Commitments and contingencies
Stockholders' equity:
Additional paid-in capital		$ 1,367,434		$ 1,362,684
Accumulated deficit		(366,607)		(440,699)
Accumulated other comprehensive income (loss)		46,445		86,784
Total stockholders' equity		1,047,272		1,008,769
Total liabilities and stockholders' equity		1,754,171		1,574,087
Non-Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents		194		152	$ 244		$ 640
Accounts receivable		31		33
Other current assets		69		6
Total current assets		294		191
Oil and gas properties, full cost method:
Proved		44,447
Less: accumulated DD&A		(44,447)
Unevaluated		2,162		36,579
Deferred taxes	[1]	16,266
Other assets, net		1,548		5,007
Investment in subsidiary		20,083		41,638
Total assets		40,353		$ 83,415
Current liabilities:
Accounts payable to vendors		9,732
Total current liabilities		9,732
Total liabilities		$ 9,732
Commitments and contingencies
Stockholders' equity:
Additional paid-in capital		$ 100,023		$ 90,339
Accumulated deficit		(57,824)		12
Accumulated other comprehensive income (loss)		(11,578)		(6,936)
Total stockholders' equity		30,621		83,415
Total liabilities and stockholders' equity		40,353		83,415
Eliminations [Member]
Current assets:
Accounts receivable		(213,906)
Deferred taxes	[1]			(4,095)
Total current assets		(213,906)		(4,095)
Oil and gas properties, full cost method:
Deferred taxes	[1]	(16,266)
Investment in subsidiary		(1,077,893)		(1,092,184)
Total assets		(1,308,065)		(1,096,279)
Current liabilities:
Accounts payable to vendors		(213,906)
Deferred taxes	[1]			(4,095)
Total current liabilities		(213,906)		(4,095)
Deferred taxes	[1]	(16,266)
Total liabilities		$ (230,172)		$ (4,095)
Commitments and contingencies
Stockholders' equity:
Additional paid-in capital		$ (1,467,457)		$ (1,453,023)
Accumulated deficit		424,431		440,687
Accumulated other comprehensive income (loss)		(34,867)		(79,848)
Total stockholders' equity		(1,077,893)		(1,092,184)
Total liabilities and stockholders' equity		$ (1,308,065)		$ (1,096,279)

[1] Deferred income taxes have been allocated to our Guarantor Subsidiaries where related oil and gas properties reside.