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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, 2024 | Dec. 31, 2023
--- | --- | ---
Investment Securities [Line Items] |  |
Amortized Cost | $ 1,234,213 | $ 1,138,425
Gross Unrealized Gains | 10,278 | 8,182
Gross Unrealized Losses | (103,691) | (125,621)
Debt Securities, Available-for-Sale | 1,140,800 | 1,020,986
US Government Agencies Residential Mortgage-backed Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 3,209 | 3,565
Gross Unrealized Gains | 33 | 47
Gross Unrealized Losses | (126) | (147)
Debt Securities, Available-for-Sale | 3,116 | 3,465
US Government Agency Debt Securities Commercial [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 724,019 | 512,979
Gross Unrealized Gains | 6,683 | 4,935
Gross Unrealized Losses | (45,868) | (52,521)
Debt Securities, Available-for-Sale | 684,834 | 465,393
Residential Mortgage Backed Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 434,676 | 559,769
Gross Unrealized Gains | 2,236 | 3,052
Gross Unrealized Losses | (53,457) | (68,222)
Debt Securities, Available-for-Sale | 383,455 | 494,599
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 | (53) | (85)
Debt Securities, Available-for-Sale | 947 | 915
Obligations of States and Political Subdivisions [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 8,962 | 9,226
Gross Unrealized Gains | 2 | 3
Gross Unrealized Losses | (785) | (1,027)
Debt Securities, Available-for-Sale | 8,179 | 8,202
Corporate Debt Securities [Member] |  |
Investment Securities [Line Items] |  |
Amortized Cost | 62,347 | 51,886
Gross Unrealized Gains | 1,324 | 145
Gross Unrealized Losses | (3,402) | (3,619)
Debt Securities, Available-for-Sale | $ 60,269 | $ 48,412

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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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