Derivative Instruments - Effect of Corporation's Derivative Financial Instruments on Income Statement (Detail) (Interest Rate Contracts [Member], Other Income [Member], USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Interest Rate Contracts [Member] | Other Income [Member]
Derivative [Line Items]
Interest Rate Products	$ 820	$ 368