Assets and Liabilities Fair Value Measurements (Parenthetical) (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans, specific reserves	$ 1.6	$ 1.9
Fair Value, Inputs, Level 2 | Fair Value Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans, specific reserves	$ 0.3	$ 0.6