Securities - Schedule of Allowance for Credit Losses on Held-to-maturity Securities (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items]
Ending balance at March 31, 2020	$ 236
ASU 2016-13 [Member]
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items]
Beginning balance at January 1, 2020	229
Current period provision	7
Ending balance at March 31, 2020	236
ASU 2016-13 [Member] | Obligations of State and Political Subdivisions [Member]
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items]
Beginning balance at January 1, 2020	96
Current period provision	2
Ending balance at March 31, 2020	98
ASU 2016-13 [Member] | Corporate Debt Securities [Member]
Debt Securities Heldtomaturity Allowance For Credit Loss [Line Items]
Beginning balance at January 1, 2020	133
Current period provision	5
Ending balance at March 31, 2020	$ 138