Investment in Securities - Schedule of the Fair Values of Securities with Unrealized Losses (Details) $ in Thousands	Sep. 30, 2021 USD ($)
Marketable Securities [Line Items]
AFS, Less than 12 months, Estimated Fair Value	$ 167,725
AFS, Less than 12 months, Unrealized Losses	2,150
AFS, 12 months or more, Estimated Fair Value	0
AFS, 12 months or more, Unrealized Losses	0
AFS, Total Estimated Fair Value	167,725
AFS, Total Unrealized Losses	2,150
State and political subdivisions
Marketable Securities [Line Items]
AFS, Less than 12 months, Estimated Fair Value	68,399
AFS, Less than 12 months, Unrealized Losses	821
AFS, 12 months or more, Estimated Fair Value	0
AFS, 12 months or more, Unrealized Losses	0
AFS, Total Estimated Fair Value	68,399
AFS, Total Unrealized Losses	821
U.S. government agencies
Marketable Securities [Line Items]
AFS, Less than 12 months, Estimated Fair Value	88,386
AFS, Less than 12 months, Unrealized Losses	1,288
AFS, 12 months or more, Estimated Fair Value	0
AFS, 12 months or more, Unrealized Losses	0
AFS, Total Estimated Fair Value	88,386
AFS, Total Unrealized Losses	1,288
Corporate Bonds
Marketable Securities [Line Items]
AFS, Less than 12 months, Estimated Fair Value	10,940
AFS, Less than 12 months, Unrealized Losses	41
AFS, 12 months or more, Estimated Fair Value	0
AFS, 12 months or more, Unrealized Losses	0
AFS, Total Estimated Fair Value	10,940
AFS, Total Unrealized Losses	$ 41