Investment Securities - Analysis of Amortized Cost and Estimated Fair Values of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Investment Securities [Line Items]
Amortized Cost	$ 1,117,384	$ 805,515
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	15,696	25,708
Gross Unrealized Losses	(8,124)	0
Securities available for sale, at fair value	1,124,956	831,223
US Government Agencies Residential Mortgage-backed Securities [Member]
Investment Securities [Line Items]
Amortized Cost	5,448	6,492
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	534	738
Gross Unrealized Losses	0	0
Securities available for sale, at fair value	5,982	7,230
US Government Agency Debt Securities Commercial [Member]
Investment Securities [Line Items]
Amortized Cost	390,566	182,823
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	4,588	8,357
Gross Unrealized Losses	(1,447)	0
Securities available for sale, at fair value	393,707	191,180
Residential Mortgage Backed Securities [Member]
Investment Securities [Line Items]
Amortized Cost	682,677	481,109
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	9,296	14,924
Gross Unrealized Losses	(6,547)	0
Securities available for sale, at fair value	685,426	496,033
US Government-sponsored Enterprises Debt Securities [Member]
Investment Securities [Line Items]
Amortized Cost	1,000	100,996
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	2
Gross Unrealized Losses	(9)	0
Securities available for sale, at fair value	991	100,998
Obligations of States and Political Subdivisions [Member]
Investment Securities [Line Items]
Amortized Cost	9,586	11,154
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	105	243
Gross Unrealized Losses	(81)	0
Securities available for sale, at fair value	9,610	11,397
Corporate Debt Securities [Member]
Investment Securities [Line Items]
Amortized Cost	28,107	22,941
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1,173	1,444
Gross Unrealized Losses	(40)	0
Securities available for sale, at fair value	$ 29,240	$ 24,385

Investment Securities [Line Items]

No definition available.

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- Definition

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).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

+ Details

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- Definition

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).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

+ Details

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

No definition available.

+ Details

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

+ Details

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