Reconciliation of Asset Retirement Obligations which are Included in Other Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$ 6,437		$ 4,513
Changes in estimates	112		0
Liabilities incurred	238	[1]	1,675	[1]
Liabilities settled	(92)		(220)
Sale of properties	(1,224)		0
Accretion expense	419		469
Balance at end of year	5,890		6,437
Eagle Ford Shale
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Liabilities incurred			$ 1,500

[1] Includes $1.5 million recognized in 2013 in connection with the EF Acquisition.