Mortgage Banking Activities - Valuation Allowance for Mortgage Servicing Rights (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Mortgage Banking [Abstract]
Balance, beginning of period		$ (39)
Impairment charges	$ (3)	(435)
Balance, end of period	$ (3)	$ (474)