Derivative Financial Instruments - Details of Derivative Contracts (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Zero cost collar one [Member]
Derivative [Line Items]
Date of transaction	Apr. 05, 2013
Type of derivative	Zero cost collar
Total notional amount	$ 54,000
Month of settlement	July to September 2014
Zero cost collar two [Member]
Derivative [Line Items]
Date of transaction	May 29, 2013
Type of derivative	Zero cost collar
Total notional amount	54,000
Month of settlement	October to December 2014
Zero cost collar three [Member]
Derivative [Line Items]
Date of transaction	Mar. 12, 2014
Type of derivative	Zero cost collar
Total notional amount	$ 54,000
Month of settlement	January to March 2015