Investment Securities - Reconciliation of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 799,996	$ 752,260
Gross Unrealized Gains	17,600	5,785
Gross Unrealized Losses	(4,506)	(2,145)
Investment securities available for sale, at fair value	813,090	755,900
U.S. Treasury and U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	155,853	135,361
Gross Unrealized Gains	1,807	722
Gross Unrealized Losses	(319)	(436)
Investment securities available for sale, at fair value	157,341	135,647
Mortgage-backed securities, residential
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	461,700	500,245
Gross Unrealized Gains	13,156	3,185
Gross Unrealized Losses	(1,305)	(1,551)
Investment securities available for sale, at fair value	473,551	501,879
Mortgage-backed securities, multifamily
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	53,026	48,675
Gross Unrealized Gains	1,500	633
Gross Unrealized Losses	(18)	(123)
Investment securities available for sale, at fair value	54,508	49,185
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	43,064	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,951)	0
Investment securities available for sale, at fair value	41,113	0
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	77,353	58,979
Gross Unrealized Gains	1,023	1,077
Gross Unrealized Losses	(913)	(35)
Investment securities available for sale, at fair value	77,463	60,021
Debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,000	9,000
Gross Unrealized Gains	114	168
Gross Unrealized Losses	0	0
Investment securities available for sale, at fair value	$ 9,114	$ 9,168

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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