Derivative Financial Instruments - Additional Information (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net derivatives	$ 42,149,000	$ 3,517,000
Amount to be reclassed to interest expense during next twelve months	20,500,000
Cash collateral held	450,000	5,190,000
Cash collateral pledged	$ 46,377,000	$ 40,000