Cash Flow Information - Supplemental Information on Cash Flows and Noncash Transactions (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental cash flow information:
Interest paid	$ 5,419	$ 8,664	$ 13,802
Federal income taxes paid	20,779	18,942	18,844
Schedule of noncash investing and financing activities:
Assets acquired through foreclosure	2,459	6,013	11,017
Investment securities purchased but not settled	$ 8,589	$ 21,325	$ 14,945