Derivative Financial Instruments - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2015 USD ($)	Dec. 31, 2014 Contracts
Derivative [Line Items]
Number of derivative contracts | Contracts		0
Estimated amount reclassified from accumulated other comprehensive income into earnings, period	12 months
Estimated amount reclassified from accumulated other comprehensive income into earnings	$ 1,417,000
Hedge collateral	6,380,000
Zero cost collars [Member]
Derivative [Line Items]
Deposit with counterparty	5,000,000
Threshold amount of cash collateral	500,000
Cash collateral for credit exposure in derivatives	1,400,000
Hedge collateral	6,380,000
Termination provisions for cash and cash equivalents	$ 30,000,000