Investment Securities - Reconciliation of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 661,284	$ 649,741
Gross Unrealized Gains	5,362	1,078
Gross Unrealized Losses	(2,524)	(12,201)
Investment securities available for sale, at fair value	664,122	638,618
U.S. Treasury and U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	139,884	143,495
Gross Unrealized Gains	587	0
Gross Unrealized Losses	(601)	(2,568)
Investment securities available for sale, at fair value	139,870	140,927
Mortgage-backed securities, residential
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	433,109	434,208
Gross Unrealized Gains	3,420	779
Gross Unrealized Losses	(1,857)	(8,843)
Investment securities available for sale, at fair value	434,672	426,144
Mortgage-backed securities, multifamily
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	38,548	21,087
Gross Unrealized Gains	591	67
Gross Unrealized Losses	(25)	(204)
Investment securities available for sale, at fair value	39,114	20,950
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	44,743	45,951
Gross Unrealized Gains	641	140
Gross Unrealized Losses	(41)	(586)
Investment securities available for sale, at fair value	45,343	45,505
Debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,000	5,000
Gross Unrealized Gains	123	92
Gross Unrealized Losses	0	0
Investment securities available for sale, at fair value	$ 5,123	$ 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
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-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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