Interest-bearing Time Deposits in Banks and Securities - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Interest Bearing Time Deposits In Banks And Securities [Line Items]
INTEREST-BEARING TIME DEPOSITS IN BANKS	$ 45,172,000	$ 62,018,000	$ 49,005,000
Time deposits with balances greater than $100,000	40,943,000		44,776,000
Time deposits balances	100,000		100,000
Number of investment positions	108
Securities pledged as collateral	870,328,000
Sales of investment securities available-for-sale	5,227,000	21,003,000
Gross realized gains from securities sales and calls	223,000	346,000
Gross realized losses from securities sales and calls	$ 1,000	$ 0
Minimum [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Interesting-bearing time deposits, maturity period, years	One
Maximum [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Interesting-bearing time deposits, maturity period, years	Two