Other Real Estate Owned - Activity in Other Real Estate Owned (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Regulatory Assets [Abstract]
Balance at beginning of period	$ 3,729	$ 11,071	$ 8,810	$ 18,546
Additions	474	1,745	1,649	2,695
Sales	(511)	(2,143)	(6,136)	(8,695)
Impairment	(129)	(414)	(760)	(2,287)
Balance at end of period	$ 3,563	$ 10,259	$ 3,563	$ 10,259