Supplemental Crude Oil and Natural Gas Information - Schedule of Proved Crude Oil and Natural Gas Reserves (Detail)	12 Months Ended
	Dec. 31, 2014 MMcf MBoe	Dec. 31, 2013 MBoe	Dec. 31, 2012 MBoe
Reserve Quantities [Line Items]
Percentage of discounted future net cash flows prepared by external reserve engineers	99.00%	99.00%	99.00%
Changes in Proved Reserves [Roll Forward]
Revisions of previous estimates	315
Proved reserves at beginning of period, Total	1,084,125	784,677	508,438
Revisions of previous estimates, Total	(107,949)	(96,054)	4,149
Extensions, discoveries and other additions, Total	440,621	444,654	233,652
Production, Total	(63,579)	(49,610)	(35,716)
Sales of minerals in place, Total	(3,227)	0	(7,838)
Purchases of minerals in place, Total	1,100	458	81,992
Proved reserves at end of period, Total	1,351,091	1,084,125	784,677
Percent of proved crude oil reserve estimates prepared by external reserve engineers	99.00%
Percent of proved natural gas reserve estimates prepared by external reserve engineers	95.00%
Natural Gas [Member]
Changes in Proved Reserves [Roll Forward]
Proved reserves at beginning of period	2,078,020	1,341,084	1,093,832
Revisions of previous estimates	(244,783)	(241,623)	(174,736)
Extensions, discoveries and other additions	1,206,569	1,065,870	400,848
Production	(114,295)	(87,730)	(63,875)
Sales of minerals in place	(18,623)	0	(4,046)
Purchases of minerals in place	1,498	419	89,061
Proved reserves at end of period	2,908,386	2,078,020	1,341,084
Crude Oil [Member]
Changes in Proved Reserves [Roll Forward]
Proved reserves at beginning of period	737,788	561,163	326,133
Revisions of previous estimates	(67,151)	(55,783)	33,272
Extensions, discoveries and other additions	239,526	267,009	166,844
Production	(44,530)	(34,989)	(25,070)
Sales of minerals in place	(123)	0	(7,165)
Purchases of minerals in place	850	388	67,149
Proved reserves at end of period	866,360	737,788	561,163