Fair Values of Financial Instruments - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value Measurements Disclosure [Line Items]
Securities held to maturity, carrying value	$ 645,164	$ 639,631
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Measurements Disclosure [Line Items]
Recognized impairment	300
Securities held to maturity, carrying value	300
Securities held to maturity, fair value	$ 500