Investment Securities - Reconciliation of Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 97,893	$ 123,975
Gross Unrealized Gains	3,313	1,115
Gross Unrealized Losses	(1)	(186)
Fair Value	101,205	124,904
U.S. government agencies
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	25,805	31,335
Gross Unrealized Gains	853	182
Gross Unrealized Losses	0	(8)
Fair Value	26,658	31,509
Mortgage-backed securities, residential
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	60,737	76,229
Gross Unrealized Gains	2,133	734
Gross Unrealized Losses	(1)	(176)
Fair Value	62,869	76,787
Mortgage-backed securities, multifamily
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	717	1,750
Gross Unrealized Gains	54	4
Gross Unrealized Losses	0	(2)
Fair Value	771	1,752
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	8,134	12,161
Gross Unrealized Gains	273	195
Gross Unrealized Losses	0	0
Fair Value	8,407	12,356
Debt securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,500	2,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 2,500	$ 2,500