Loans and Allowance for Loan Losses - Schedule of Activity of Purchased Impaired Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
Purchased impaired loans	$ 38,180	$ 55,419
Allowance for loan losses	(198)	(278)
Carrying amount, net of allowance	37,982	55,141
Commercial Loan [Member]
Financing Receivable, Impaired [Line Items]
Purchased impaired loans	594	850
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Purchased impaired loans	19,855	32,774
Residential [Member]
Financing Receivable, Impaired [Line Items]
Purchased impaired loans	11,867	13,580
Consumer Loan [Member]
Financing Receivable, Impaired [Line Items]
Purchased impaired loans	$ 5,864	$ 8,215