Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 1 to Level 2	$ 0	$ 0
Transfers from Level 2 to Level 1	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
AFS securities [Abstract]
AFS Securities	1,255,925	1,338,290
Trading securities	11,467	9,259
Liabilities [Abstract]
Collateral dependent impaired financing receivable with specific reserves	100	7,000
Reserves on collateral dependent impaired loans	$ 100	1,500
Minimum [Member]
Liabilities [Abstract]
Liquidation expense ratio on impaired collateral	10.00%
Maximum [Member]
Liabilities [Abstract]
Liquidation expense ratio on impaired collateral	35.00%
Federal Agency [Member]
AFS securities [Abstract]
AFS Securities	$ 108,899	174,408
State & Municipal [Member]
AFS securities [Abstract]
AFS Securities	41,956	46,726
Other Securities [Member]
AFS securities [Abstract]
AFS Securities	14,149	20,739
Recurring Basis [Member]
AFS securities [Abstract]
AFS Securities	1,255,925	1,338,290
Trading securities	11,467	9,259
Derivatives	3,732	3,210
Total	1,271,124	1,350,759
Liabilities [Abstract]
Derivatives	324	506
Total	324	506
Recurring Basis [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	5,845	11,493
Trading securities	11,467	9,259
Derivatives	0	0
Total	17,312	20,752
Liabilities [Abstract]
Derivatives	0	0
Total	0	0
Recurring Basis [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	1,250,080	1,326,797
Trading securities	0	0
Derivatives	3,732	3,210
Total	1,253,812	1,330,007
Liabilities [Abstract]
Derivatives	324	506
Total	324	506
Recurring Basis [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0
Trading securities	0	0
Derivatives	0	0
Total	0	0
Liabilities [Abstract]
Derivatives	0	0
Total	0	0
Recurring Basis [Member] \| Federal Agency [Member]
AFS securities [Abstract]
AFS Securities	108,899	174,408
Recurring Basis [Member] \| Federal Agency [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	0	0
Recurring Basis [Member] \| Federal Agency [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	108,899	174,408
Recurring Basis [Member] \| Federal Agency [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0
Recurring Basis [Member] \| State & Municipal [Member]
AFS securities [Abstract]
AFS Securities	41,956	46,726
Recurring Basis [Member] \| State & Municipal [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	0	0
Recurring Basis [Member] \| State & Municipal [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	41,956	46,726
Recurring Basis [Member] \| State & Municipal [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0
Recurring Basis [Member] \| Mortgage-Backed [Member]
AFS securities [Abstract]
AFS Securities	554,927	529,844
Recurring Basis [Member] \| Mortgage-Backed [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	0	0
Recurring Basis [Member] \| Mortgage-Backed [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	554,927	529,844
Recurring Basis [Member] \| Mortgage-Backed [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0
Recurring Basis [Member] \| Collateralized Mortgage Obligations [Member]
AFS securities [Abstract]
AFS Securities	535,994	566,573
Recurring Basis [Member] \| Collateralized Mortgage Obligations [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	0	0
Recurring Basis [Member] \| Collateralized Mortgage Obligations [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	535,994	566,573
Recurring Basis [Member] \| Collateralized Mortgage Obligations [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0
Recurring Basis [Member] \| Other Securities [Member]
AFS securities [Abstract]
AFS Securities	14,149	20,739
Recurring Basis [Member] \| Other Securities [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	5,845	11,493
Recurring Basis [Member] \| Other Securities [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	8,304	9,246
Recurring Basis [Member] \| Other Securities [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	$ 0	$ 0

Collateral dependent impaired loans with specific reserves included in the allowance for loan losses.

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Collateral dependent impaired loans which had specific reserves.

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The percentage of liquidation expenses estimated with liquidating impaired collateral.

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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

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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.

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Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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Fair value of financial and nonfinancial obligations.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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