Deposits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Banking and Thrift [Abstract]
Certificates of deposit over $100 thousand	$ 1,700.0	$ 1,400.0
Interest expense on time deposits of $100 thousand or more	4.0	5.9	$ 7.9
Deposits from certain directors, executive officers and their affiliates	$ 57.3	$ 57.7