Securities Available-for-Sale - Revenue Bonds by Type (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 592,378	$ 569,942
Fair Market Value	600,799	560,479
States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	181,900	140,181
Fair Market Value	188,265	140,534
Revenue Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	25,861	23,890
Fair Market Value	26,678	23,901
Revenue Bonds [Member] | Water [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,515	6,942
Fair Market Value	7,775	6,946
Revenue Bonds [Member] | College & University [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,997	2,583
Fair Market Value	2,019	2,604
Revenue Bonds [Member] | Sales Tax [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,949	2,932
Fair Market Value	1,995	2,901
Revenue Bonds [Member] | Lease [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,596	2,053
Fair Market Value	3,678	2,068
Revenue Bonds [Member] | Electricity [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,421	1,027
Fair Market Value	1,521	1,047
Revenue Bonds [Member] | Sewer [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,760	1,392
Fair Market Value	4,811	1,398
Revenue Bonds [Member] | Other Revenue Source [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,623	6,961
Fair Market Value	$ 4,879	$ 6,937