Investment Securities - Income Earned on Securities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Non-taxable:
Total	$ 30,717	$ 14,910	$ 79,418	$ 47,326
Held-to-maturity
Taxable:
Taxable	1,127	256	2,477	715
Non-taxable:
Non-taxable	4,853	65	9,887	205
Available-for-sale
Taxable:
Taxable	15,949	6,937	39,313	26,604
Non-taxable:
Non-taxable	$ 8,788	$ 7,652	$ 27,741	$ 19,802

Interest income, securities, operating, by non-0taxable status [abstract]

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.2)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

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-Publisher SEC
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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 before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(b))
-URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 22
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