Investment Securities - Reconciliation of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 715,656	$ 649,741
Gross Unrealized Gains	6,694	1,078
Gross Unrealized Losses	(1,945)	(12,201)
Investment securities available for sale, at fair value	720,405	638,618
U.S. Treasury and U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	145,976	143,495
Gross Unrealized Gains	846	0
Gross Unrealized Losses	(492)	(2,568)
Investment securities available for sale, at fair value	146,330	140,927
Mortgage-backed securities, residential
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	471,178	434,208
Gross Unrealized Gains	4,171	779
Gross Unrealized Losses	(1,341)	(8,843)
Investment securities available for sale, at fair value	474,008	426,144
Mortgage-backed securities, multifamily
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	50,164	21,087
Gross Unrealized Gains	818	67
Gross Unrealized Losses	(92)	(204)
Investment securities available for sale, at fair value	50,890	20,950
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	43,338	45,951
Gross Unrealized Gains	726	140
Gross Unrealized Losses	(20)	(586)
Investment securities available for sale, at fair value	44,044	45,505
Debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,000	5,000
Gross Unrealized Gains	133	92
Gross Unrealized Losses	0	0
Investment securities available for sale, at fair value	$ 5,133	$ 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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-Publisher FASB
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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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