Investment in Securities (Schedule of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Fair Value	$ 454,981	$ 470,523
Gross Unrealized Gains	3,582	9,528
Gross Unrealized Losses	5,224	1,383
Amortized Cost	456,623	462,378
State and Political Subdivisions [Member]
Investment [Line Items]
Fair Value	395,340	417,032
Gross Unrealized Gains	3,582	9,528
Gross Unrealized Losses	3,681	661
Amortized Cost	395,439	408,165
U.S. government agencies [Member]
Investment [Line Items]
Fair Value	52,400	45,500
Gross Unrealized Gains
Gross Unrealized Losses	1,543	722
Amortized Cost	53,943	46,222
Certificates of Deposit [Member]
Investment [Line Items]
Fair Value	7,241	7,991
Gross Unrealized Gains
Gross Unrealized Losses
Amortized Cost	$ 7,241	$ 7,991

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- Definition

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

+ References

No definition available.

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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=82897076&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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