Deposits - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Banking and Thrift [Abstract]
Certificates of deposit over $100 thousand	$ 1,400,000,000	$ 1,000,000,000
Interest expense on time deposits of $100 thousand or more	5,900,000	7,900,000	8,200,000
Deposits from certain directors, executive officers and their affiliates	$ 57,700,000	$ 62,900,000