Interest-Bearing Deposits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deposits [Abstract]
Interest-bearing demand deposit, money market	$ 1,200.0	$ 1,100.0
Certificates of deposit in denominations of $100 thousand or more	93.1	143.9
Interest expense related to certificates of deposit $100 thousand or greater	2.0	3.3	$ 1.6
Deposit Liabilities Reclassified as Loans Receivable	$ 0.7	$ 0.9