Investment Securities - Proceeds from Calls and Sales, Realized Gains and Losses and Interest Income Narrative (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Proceeds from calls and sales of investment securities
Proceeds from calls of investment securities	$ 40.2	$ 10.3
Proceeds from sales of investment securities	0.0	0.0
Gross realized gains and losses on investment securities
Gross realized gains on sales of investment securities	0.0	0.0
Gross realized losses on sales of investment securities	0.0	0.0
Income tax expense related to the Company's net realized gain on the sale of investment securities	0.0	0.0
Interest income from taxable and nontaxable investment securities
Interest income from taxable investment securities	26.7	29.1
Interest income from non-taxable investment securities	$ 3.1	$ 3.2

Amount of realized gain on investment in debt security and equity securities.

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Amount of realized loss on investment in debt security and equity securities.

+ References

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The cash inflow associated with calls on debt securities.

+ References

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Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities exempt from state, federal and other income tax.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1402
-Paragraph a
-Publisher SEC

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-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478524/942-220-S99-1

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-Number 229
-Section 1402
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Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities subject to state, federal and other income tax.

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 10
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Amount of cash inflow from sale 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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
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-Name Accounting Standards Codification
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