Investment Securities - Reconciliation of Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 84,994	$ 90,766
Gross Unrealized Gains	2,492	3,114
Gross Unrealized Losses	(271)	(12)
Allowance for Credit Losses	0	0	$ 0	$ 0
Fair Value	87,215	93,868
U.S. government agencies
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	25,453	25,565
Gross Unrealized Gains	604	779
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0	0
Fair Value	26,057	26,344
Mortgage-backed securities, residential
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	36,965	39,276
Gross Unrealized Gains	1,193	1,469
Gross Unrealized Losses	(271)	(12)
Allowance for Credit Losses	0	0
Fair Value	37,887	40,733
Collateralized mortgage obligations, residential
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	11,437	14,590
Gross Unrealized Gains	417	532
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0	0
Fair Value	11,854	15,122
Mortgage-backed securities, multifamily
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	693	705
Gross Unrealized Gains	37	54
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0	0
Fair Value	730	759
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	10,446	10,630
Gross Unrealized Gains	241	280
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0	0
Fair Value	$ 10,687	$ 10,910