Interest-Bearing Time Deposits in Banks and Securities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest Bearing Time Deposits In Banks And Securities [Line Items]
INTEREST-BEARING TIME DEPOSITS IN BANKS	$ 49,005,000	$ 61,175,000
Interesting-bearing deposits, maturity period, years	90 days or less
Time deposits with balances greater than $100,000	44,776,000	51,813,000
Time deposits balances	100,000	100,000
Number of investment positions	90
Securities pledged as collateral	843,859,000	829,074,000
Sales of investment securities available-for-sale	144,144,000	22,970,000	28,039,000
Gross realized gains from securities sales and calls	2,816,000	505,000	363,000
Gross realized losses from sales	$ 44,000	$ 13,000	$ 0
Minimum [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Interesting-bearing deposits, maturity period, years	One
Maximum [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Interesting-bearing deposits, maturity period, years	Two