Borrowings - Customer Repurchase Agreements (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Disclosure [Abstract]
Customer repurchase agreements	$ 24,211	$ 41,974	$ 37,256
Weighted average interest rate at year end	0.05%	0.06%	0.07%
Maximum amount outstanding at any month's end	$ 43,161	$ 43,266	$ 110,228
Average amount outstanding during the year	$ 30,720	$ 41,048	$ 72,211
Weighted average interest rate during the year	0.05%	0.06%	0.06%