Loans and Allowance for Loan Losses - Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012	Mar. 31, 2012
Receivables [Abstract]
Non-accrual loans	$ 22,509		$ 21,800	$ 20,963
Loans still accruing and past due 90 days or more	24		97	53
Restructured loans		[1]
Total	$ 22,533		$ 21,897	$ 21,016

[1] Restructured loans whose interest collection, after considering economic and business conditions and collection efforts, is doubtful are included in non-accrual loans.