Fair Value - Reconciliation of All Assets Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - Significant Unobservable Inputs (Level 3) [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Pooled Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 8,448	$ 8,119
Accretion (amortization) of discount	17	17
Sales/payments received	(338)	(424)
Increase in fair value of securities	368	736
Transfers into Level 3	0
Balance at end of period	8,495	8,448
State and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	0	0
Accretion (amortization) of discount	(56)	0
Sales/payments received	0	0
Increase in fair value of securities	28	0
Transfers into Level 3	4,136
Balance at end of period	$ 4,108	$ 0