Investment in Securities - Schedule of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Amortized Cost	$ 528,531	$ 338,047
Gross Unrealized Gains	14,698	19,679
Gross Unrealized Losses	2,150	0
Fair Value	541,079	357,726
State and political subdivisions
Marketable Securities [Line Items]
Amortized Cost	345,165	287,059
Gross Unrealized Gains	13,880	18,915
Gross Unrealized Losses	821	0
Fair Value	358,224	305,974
U.S. government agencies
Marketable Securities [Line Items]
Amortized Cost	112,850	50,988
Gross Unrealized Gains	537	764
Gross Unrealized Losses	1,288	0
Fair Value	112,099	$ 51,752
Corporate Bonds
Marketable Securities [Line Items]
Amortized Cost	70,516
Gross Unrealized Gains	281
Gross Unrealized Losses	41
Fair Value	$ 70,756

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).

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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).

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Amortized cost excluding accrued interest, after allowance for credit loss, of 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/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
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-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

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Amount excluding accrued interest, 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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