Investment in Securities (Schedule of Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Marketable Securities [Line Items]
Fair Value	$ 422,665	$ 441,534
Gross Unrealized Gains	14,234	3,877
Gross Unrealized Losses	169	3,223
Amortized Cost	408,600	440,880
State and Political Subdivisions [Member]
Marketable Securities [Line Items]
Fair Value	324,447	334,717
Gross Unrealized Gains	13,727	3,791
Gross Unrealized Losses		1,806
Amortized Cost	310,720	332,732
U.S. government agencies [Member]
Marketable Securities [Line Items]
Fair Value	97,718	104,822
Gross Unrealized Gains	507	86
Gross Unrealized Losses	169	1,417
Amortized Cost	97,380	106,153
Certificates of Deposit [Member]
Marketable Securities [Line Items]
Fair Value	500	1,995
Gross Unrealized Gains
Gross Unrealized Losses
Amortized Cost	$ 500	$ 1,995

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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