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Investment Securities - Analysis of Amortized Cost and Estimated Fair Values of Securities Available for Sale (Detail) - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Investment Securities [Line Items] |  |
Amortized Cost | $ 978,690 | $ 898,702
Gross Unrealized Gains | 11 | 275
Gross Unrealized Losses | (161,098) | (136,316)
Debt Securities, Available-for-Sale | 817,603 | 762,661
US Government Agencies Residential Mortgage-backed Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 3,678 | 4,127
Gross Unrealized Gains | 10 | 37
Gross Unrealized Losses | (262) | (181)
Debt Securities, Available-for-Sale | 3,426 | 3,983
US Government Agency Debt Securities Commercial [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 429,282 | 324,306
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (64,471) | (52,890)
Debt Securities, Available-for-Sale | 364,811 | 271,416
Residential Mortgage Backed Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 501,750 | 527,777
Gross Unrealized Gains | 1 | 59
Gross Unrealized Losses | (90,493) | (78,847)
Debt Securities, Available-for-Sale | 411,258 | 448,989
US Government-sponsored Enterprises Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 1,000 | 1,000
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (113) | (118)
Debt Securities, Available-for-Sale | 887 | 882
Obligations of States and Political Subdivisions [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 9,228 | 9,482
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (1,475) | (1,295)
Debt Securities, Available-for-Sale | 7,753 | 8,187
Corporate Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 33,752 | 32,010
Gross Unrealized Gains | 0 | 179
Gross Unrealized Losses | (4,284) | (2,985)
Debt Securities, Available-for-Sale | $ 29,468 | $ 29,204

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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://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481800/320-10-50-2 + 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://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481800/320-10-50-2 + Details
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