Interest-bearing Time Deposits in Banks and Securities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014 Investment	Dec. 31, 2013	Dec. 31, 2012
Interest Bearing Time Deposits In Banks And Securities [Line Items]
INTEREST-BEARING TIME DEPOSITS IN BANKS	$ 17,002,000	$ 31,917,000
Time deposits with balances greater than $100,000	15,467,000	29,002,000
Time deposits balances	100,000	100,000
Held-to-maturity securities	441,000	684,000
Number of investment positions	86
Securities pledged as collateral	1,600,682,000	1,147,955,000
Sales of investment securities available-for-sale	1,619,000	122,025,000	144,144,000
Gross realized gains from security sales	2,000	1,376,000	2,816,000
Gross realized losses from security sales	$ 6,000	$ 1,229,000	$ 44,000
Minimum [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Interest-bearing time deposits, maturity period, years	1 year
Maximum [Member]
Interest Bearing Time Deposits In Banks And Securities [Line Items]
Interest-bearing time deposits, maturity period, years	2 years