Capitalized Mortgage Servicing rights (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Participating Mortgage Loans [Line Items]
Balance, beginning of year	$ 6,087	$ 7,800	$ 8,430
Additions	2,122	1,307	2,638
Amortized to expense	(3,290)	(2,817)	(3,268)
Change in valuation allowance	(142)	(203)
Balance, end of year	$ 4,777	$ 6,087	$ 7,800