Guarantor Financial Statements - Condensed Consolidating Statement of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities:
Net income	$ 25,943	$ 40,758
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	82,646	75,435
Accretion expense	7,555	8,263
Deferred income tax provision (benefit)	15,102	27,024
Settlement of asset retirement obligations	(9,842)	(14,880)
Non-cash stock compensation expense	2,247	2,296
Excess tax benefits		(104)
Non-cash derivative expense	448	1,385
Non-cash interest expense	4,070	4,041
Non-cash (income) loss from investment in subsidiaries
Change in current income taxes		(9,402)
Change in intercompany receivables/payables
(Increase) decrease in accounts receivable	(18,602)	19,952
Decrease in other current assets	100	40
(Increase) decrease in inventory	(928)	158
Increase (decrease) in accounts payable	1,293	2,004
Increase (decrease) in other current liabilities	5,820	(8,942)
Other	(380)	(1,262)
Net cash (used in) provided by operating activities	115,472	146,766
Cash flows from investing activities:
Investment in oil and gas properties	(287,175)	(160,968)
Proceeds from sale of oil and gas properties, net of expenses	51,954
Investment in fixed and other assets	(1,654)	(599)
Change in restricted funds	(358)
Net cash used in investing activities	(237,233)	(161,567)
Cash flows from financing activities:
Deferred financing costs	(126)	(11)
Excess tax benefits		104
Net payments for share-based compensation	(6,565)	(3,465)
Net cash used in financing activities	(6,691)	(3,372)
Effect of exchange rate changes on cash	(11)
Net change in cash and cash equivalents	(128,463)	(18,173)
Cash and cash equivalents, beginning of period	331,224	279,526
Cash and cash equivalents, end of period	202,761	261,353
Parent [Member]
Cash flows from operating activities:
Net income	25,943	40,758
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	28,055	10,191
Accretion expense	68	93
Deferred income tax provision (benefit)	(5,907)	(4,941)
Non-cash stock compensation expense	2,247	2,296
Excess tax benefits		(104)
Non-cash interest expense	4,070	4,041
Non-cash (income) loss from investment in subsidiaries	(37,345)	(56,828)
Change in current income taxes		(9,402)
Change in intercompany receivables/payables	(51,037)	122,912
(Increase) decrease in accounts receivable	(24,762)	10,668
Decrease in other current assets	100	40
(Increase) decrease in inventory	(928)	158
Increase (decrease) in accounts payable	1,501	(1,890)
Increase (decrease) in other current liabilities	5,212	(20,011)
Other	145	(761)
Net cash (used in) provided by operating activities	(52,638)	97,220
Cash flows from investing activities:
Investment in oil and gas properties	(46,772)	(111,458)
Proceeds from sale of oil and gas properties, net of expenses	9,700
Investment in fixed and other assets	(1,654)	(599)
Net cash used in investing activities	(38,726)	(112,057)
Cash flows from financing activities:
Deferred financing costs	(126)	(11)
Excess tax benefits		104
Net payments for share-based compensation	(6,565)	(3,465)
Net cash used in financing activities	(6,691)	(3,372)
Net change in cash and cash equivalents	(98,055)	(18,209)
Cash and cash equivalents, beginning of period	246,294	228,398
Cash and cash equivalents, end of period	148,239	210,189
Guarantor Subsidiary [Member]
Cash flows from operating activities:
Net income	37,341	56,828
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	54,591	65,244
Accretion expense	7,487	8,170
Deferred income tax provision (benefit)	21,009	31,965
Settlement of asset retirement obligations	(9,842)	(14,880)
Non-cash derivative expense	448	1,385
Change in intercompany receivables/payables	47,637	(122,912)
(Increase) decrease in accounts receivable	6,160	9,284
Increase (decrease) in accounts payable	(208)	3,894
Increase (decrease) in other current liabilities	608	11,069
Other	(525)	(501)
Net cash (used in) provided by operating activities	164,706	49,546
Cash flows from investing activities:
Investment in oil and gas properties	(236,903)	(49,510)
Proceeds from sale of oil and gas properties, net of expenses	42,254
Net cash used in investing activities	(194,649)	(49,510)
Cash flows from financing activities:
Net change in cash and cash equivalents	(29,943)	36
Cash and cash equivalents, beginning of period	84,290	51,128
Cash and cash equivalents, end of period	54,347	51,164
Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net income	8
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization
Accretion expense
Non-cash (income) loss from investment in subsidiaries	(4)
Change in intercompany receivables/payables	3,400
Net cash (used in) provided by operating activities	3,404
Cash flows from investing activities:
Investment in oil and gas properties	(3,500)
Change in restricted funds	(358)
Investment in subsidiaries	(3,955)
Net cash used in investing activities	(7,813)
Cash flows from financing activities:
Equity proceeds from parent	3,955
Net cash used in financing activities	3,955
Effect of exchange rate changes on cash	(11)
Net change in cash and cash equivalents	(465)
Cash and cash equivalents, beginning of period	640
Cash and cash equivalents, end of period	175
Consolidation, Eliminations [Member]
Cash flows from operating activities:
Net income	(37,349)	(56,828)
Adjustments to reconcile net income to net cash provided by operating activities:
Non-cash (income) loss from investment in subsidiaries	37,349	56,828
Cash flows from investing activities:
Investment in subsidiaries	3,955
Net cash used in investing activities	3,955
Cash flows from financing activities:
Equity proceeds from parent	(3,955)
Net cash used in financing activities	(3,955)
Cash and cash equivalents, end of period