Investment Securities - Income Earned on Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest Income, Securities, Operating, by Taxable Status [Abstract]
Total	$ 57,318	$ 40,115	$ 33,479
Held-to-maturity
Interest Income, Securities, Operating, by Taxable Status [Abstract]
Taxable	2,157	2,521	3,778
Non-taxable	7,424	8,693	10,641
Available-for-sale
Interest Income, Securities, Operating, by Taxable Status [Abstract]
Taxable	40,926	25,996	17,928
Non-taxable	$ 6,811	$ 2,905	$ 1,132

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Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities exempt from state, federal and other income tax.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.2)
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Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities subject to state, federal and other income tax.

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(b))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (c)
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