Allowance for Credit Losses - Provision for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Receivables [Abstract]
Provision for loan losses	$ 1,301	$ 5,949	$ 7,413	$ 8,041
Provision for unfunded letters of credit	339	(109)	329	28
Total provision for credit losses	$ 1,640	$ 5,840	$ 7,742	$ 8,069