Cash Flow Information - Supplemental Information on Cash Flows and Noncash Transactions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental cash flow information:
Interest paid	$ 5,465	$ 4,085	$ 4,231
Federal income taxes paid	28,348	29,674	28,711
Schedule of noncash investing and financing activities:
Assets acquired through foreclosure	2,269	$ 203	1,385
Investment securities purchased but not settled	$ 12,381		$ 1,248