Goodwill and Other Intangible Assets - Schedule of Change in Loan Servicing Rights (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Balance at beginning of year	$ 20,368	$ 16,681	$ 20,446
Origination of loan servicing rights	7,039	8,479	1,696
Amortization expense	(5,323)	(4,792)	(5,461)
Balance at end of year	22,084	20,368	16,681
Balance at beginning of year	(900)	(289)	(592)
Impairment adjustment	429	(611)	303
Balance at end of year	(471)	(900)	(289)
Balance at end of year, net of valuation allowance	$ 21,613	$ 19,468	$ 16,392