Derivative Financial Instruments - Notional Amounts and Estimated Fair Values of Outstanding Derivative Positions (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities, Estimated Fair Value	$ 1,029	$ 1,801
Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, Estimated Fair Value	2,211	3,521
Oil [Member]
Derivatives, Fair Value [Line Items]
Notional Units	Barrels	Barrels
Derivative assets, Notional Amount	335	738
Derivative assets, Estimated Fair Value	827	2,568
Derivative liabilities, Notional Amount	(335)	(738)
Derivative liabilities, Estimated Fair Value	(378)	(1,591)
Natural Gas [Member]
Derivatives, Fair Value [Line Items]
Notional Units	MMBTUs	MMBTUs
Derivative assets, Notional Amount	5,128	4,431
Derivative assets, Estimated Fair Value	1,384	953
Derivative liabilities, Notional Amount	(5,128)	(4,431)
Derivative liabilities, Estimated Fair Value	$ (651)	$ (210)