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Securities - Summary of Amortized Cost and Estimated Fair Values of Debt Securities Available for Sale (Detail) - USD ($) $ in Thousands | Mar. 31, 2023 | Dec. 31, 2022
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Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | $ 1,690,430 | $ 1,631,891
Gross Unrealized Gains | 1,583 | 254
Gross Unrealized Losses | (76,100) | (93,924)
Estimated Fair Value | 1,615,913 | 1,538,221
U.S. Treasuries [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 1,629,245 | 1,568,563
Gross Unrealized Gains | 1,341 |
Gross Unrealized Losses | (72,992) | (90,699)
Estimated Fair Value | 1,557,594 | 1,477,864
U.S. Federal Agencies [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 14,072 | 15,025
Gross Unrealized Gains | 183 | 198
Gross Unrealized Losses | (1) | (1)
Estimated Fair Value | 14,254 | 15,222
Mortgage Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 17,934 | 18,449
Gross Unrealized Gains | 26 | 21
Gross Unrealized Losses | (1,773) | (1,884)
Estimated Fair Value | 16,187 | 16,586
States and Political Subdivisions [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 8,236 | 8,320
Gross Unrealized Gains | 33 | 35
Gross Unrealized Losses | (114) | (221)
Estimated Fair Value | 8,155 | 8,134
Asset backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 12,780 | 13,371
Gross Unrealized Losses | (417) | (361)
Estimated Fair Value | 12,363 | 13,010
Other Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Amortized Cost | 8,163 | 8,163
Gross Unrealized Losses | (803) | (758)
Estimated Fair Value | $ 7,360 | $ 7,405

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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 https://asc.fasb.org/extlink&oid=126970911&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 https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563 + Details
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