Mortgage Banking Activities - Valuation Allowance for Mortgage Servicing Rights (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Mortgage Banking [Abstract]
Balance, beginning of period	$ (766)	$ (12)	$ (39)	$ (58)
Impairment charges		(138)	(727)	(299)
Recoveries	25		25	207
Balance, end of period	$ (741)	$ (150)	$ (741)	$ (150)