Investment Securities - Held-To-Maturity Investment (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Held-to-maturity Securities
Amortized Cost	$ 602,687	$ 677,093
Unrealized Gains	2,112	3,856
Unrealized Losses	12,501	18,043
Held-to-maturity, fair value	592,298	662,906
State and political subdivisions
Held-to-maturity Securities
Amortized Cost	602,187	676,593
Unrealized Gains	2,112	3,856
Unrealized Losses	12,426	17,933
Held-to-maturity, fair value	591,873	662,516
Trust preferred securities
Held-to-maturity Securities
Amortized Cost	500	500
Unrealized Gains	0	0
Unrealized Losses	75	110
Held-to-maturity, fair value	$ 425	$ 390

Amount of investment in debt security measured at amortized cost (held-to-maturity).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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-Publisher FASB
-Name Accounting Standards Codification
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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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