Deposits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Banking and Thrift [Abstract]
Time deposits, $250,000 or more	$ 1,100.0	$ 647.3
Interest expense on time deposits of $250 thousand or more	6.6	1.3	$ 1.1
Deposits from certain directors, executive officers and their affiliates	$ 66.8	$ 77.7