Investment Securities - Reconciliation of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 970,699	$ 839,272
Gross Unrealized Gains	11,709	17,806
Gross Unrealized Losses	(13,870)	(1,330)
Allowance for Credit Losses	(144)	(2)	$ 0	$ 0
Total securities	968,394	855,746
U.S. Treasury and U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	92,940	63,868
Gross Unrealized Gains	1,154	1,447
Gross Unrealized Losses	(1,061)	(313)
Allowance for Credit Losses	0	0
Total securities	93,033	65,002
Mortgage-backed securities, residential
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	326,820	224,978
Gross Unrealized Gains	2,589	3,718
Gross Unrealized Losses	(5,419)	(540)
Allowance for Credit Losses	0	0
Total securities	323,990	228,156
Collateralized mortgage obligations, residential
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	179,400	204,093
Gross Unrealized Gains	4,296	4,967
Gross Unrealized Losses	(188)	(22)
Allowance for Credit Losses	0	0
Total securities	183,508	209,038
Mortgage-backed securities, multifamily
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,941	1,944
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(100)	0
Allowance for Credit Losses	0	0
Total securities	1,841	1,944
Collateralized mortgage obligations, multifamily
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	34,108	39,628
Gross Unrealized Gains	1,099	1,909
Gross Unrealized Losses	(46)	(2)
Allowance for Credit Losses	0	0
Total securities	35,161	41,535
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	40,327	40,915
Gross Unrealized Gains	8	0
Gross Unrealized Losses	(148)	(225)
Allowance for Credit Losses	0	0
Total securities	40,187	40,690
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	260,108	228,790
Gross Unrealized Gains	1,872	5,149
Gross Unrealized Losses	(6,848)	(228)
Allowance for Credit Losses	(10)	(1)
Total securities	255,122	233,710
Debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	35,055	35,056
Gross Unrealized Gains	691	616
Gross Unrealized Losses	(60)	0
Allowance for Credit Losses	(134)	(1)
Total securities	$ 35,552	$ 35,671