Nature of Operations and Summary of Significant Accounting Policies - Recent Accounting Changes (Details) - ASU 2017-12 - State and municipal securities	9 Months Ended
Sep. 30, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassificaton of investment securities held to maturity	$ (30,800,000)
Reclassification of held to maturity, gross unrealized gains	$ (450,000)

Amount of investment in debt security, measured at amortized cost, transferred to investment in debt security, measured at fair value, with change in fair value recognized in other comprehensive income (available-for-sale) and net income (trading).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27405-111563

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- Definition

Amount of unrealized gain (loss) from transfer of investment in debt security measured at amortized cost (held-to-maturity), to investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27405-111563

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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

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