Deposits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Banking and Thrift [Abstract]
Time deposits, $250,000 or more	$ 1,700.0	$ 1,100.0
Interest expense on time deposits of $250 thousand or more	5.8	6.6	$ 1.3
Deposits from certain directors, executive officers and their affiliates	$ 67.1	$ 66.8