Investment Securities - Reconciliation of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 752,260	$ 649,741
Gross Unrealized Gains	5,785	1,078
Gross Unrealized Losses	(2,145)	(12,201)
Investment securities, available for sale, at fair value	755,900	638,618
U.S. Treasury and U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	135,361	143,495
Gross Unrealized Gains	722	0
Gross Unrealized Losses	(436)	(2,568)
Investment securities, available for sale, at fair value	135,647	140,927
Mortgage-backed securities, residential
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	500,245	434,208
Gross Unrealized Gains	3,185	779
Gross Unrealized Losses	(1,551)	(8,843)
Investment securities, available for sale, at fair value	501,879	426,144
Mortgage-backed securities, multifamily
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	48,675	21,087
Gross Unrealized Gains	633	67
Gross Unrealized Losses	(123)	(204)
Investment securities, available for sale, at fair value	49,185	20,950
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	58,979	45,951
Gross Unrealized Gains	1,077	140
Gross Unrealized Losses	(35)	(586)
Investment securities, available for sale, at fair value	60,021	45,505
Debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,000	5,000
Gross Unrealized Gains	168	92
Gross Unrealized Losses	0	0
Investment securities, available for sale, at fair value	$ 9,168	$ 5,092

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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-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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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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Amortized cost of 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 of 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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