Fair Value - Reconciliation of All Assets Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
State and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers out of Level 3	$ 4,000
Transfers into Level 3		$ 4,100
Significant Unobservable Inputs (Level 3) [Member] | Pooled Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	8,495	8,448	$ 8,119
Accretion (amortization) of discount	12	17	17
Sales/payments received	(62)	(338)	(424)
Increase (decrease) in fair value of securities	(223)	368	736
Balance at end of period	8,222	8,495	$ 8,448
Significant Unobservable Inputs (Level 3) [Member] | State and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	4,108
Accretion (amortization) of discount		(56)
Sales/payments received	(35)
Increase (decrease) in fair value of securities		28
Transfers out of Level 3	(4,033)
Transfers into Level 3		4,136
Balance at end of period	$ 40	$ 4,108