Fair Value Measurements and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 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	1,357,614	1,357,614	$ 1,338,290
Trading securities	10,883	10,883	9,259
Liabilities [Abstract]
Collateral dependent impaired financing receivable with specific reserves	100	100	7,000
Allowance for loan losses for collateral dependent impaired loans with specific reserves	30	$ 30	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	139,418	$ 139,418	174,408
State & Municipal [Member]
AFS securities [Abstract]
AFS Securities	42,919	42,919	46,726
Other Securities [Member]
AFS securities [Abstract]
AFS Securities	19,739	19,739	20,739
Recurring Basis [Member]
AFS securities [Abstract]
AFS Securities	1,357,614	1,357,614	1,338,290
Trading securities	10,883	10,883	9,259
Derivatives	6,653	6,653	3,210
Total	1,375,150	1,375,150	1,350,759
Liabilities [Abstract]
Derivatives	4,128	4,128	506
Total	4,128	4,128	506
Recurring Basis [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	11,438	11,438	11,493
Trading securities	10,883	10,883	9,259
Derivatives	0	0	0
Total	22,321	22,321	20,752
Liabilities [Abstract]
Derivatives	0	0	0
Total	0	0	0
Recurring Basis [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	1,346,176	1,346,176	1,326,797
Trading securities	0	0	0
Derivatives	6,653	6,653	3,210
Total	1,352,829	1,352,829	1,330,007
Liabilities [Abstract]
Derivatives	4,128	4,128	506
Total	4,128	4,128	506
Recurring Basis [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0	0
Trading securities	0	0	0
Derivatives	0	0	0
Total	0	0	0
Liabilities [Abstract]
Derivatives	0	0	0
Total	0	0	0
Recurring Basis [Member] \| Federal Agency [Member]
AFS securities [Abstract]
AFS Securities	139,418	139,418	174,408
Recurring Basis [Member] \| Federal Agency [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	0	0	0
Recurring Basis [Member] \| Federal Agency [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	139,418	139,418	174,408
Recurring Basis [Member] \| Federal Agency [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0	0
Recurring Basis [Member] \| State & Municipal [Member]
AFS securities [Abstract]
AFS Securities	42,919	42,919	46,726
Recurring Basis [Member] \| State & Municipal [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	0	0	0
Recurring Basis [Member] \| State & Municipal [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	42,919	42,919	46,726
Recurring Basis [Member] \| State & Municipal [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0	0
Recurring Basis [Member] \| Mortgage-Backed [Member]
AFS securities [Abstract]
AFS Securities	584,226	584,226	529,844
Recurring Basis [Member] \| Mortgage-Backed [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	0	0	0
Recurring Basis [Member] \| Mortgage-Backed [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	584,226	584,226	529,844
Recurring Basis [Member] \| Mortgage-Backed [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0	0
Recurring Basis [Member] \| Collateralized Mortgage Obligations [Member]
AFS securities [Abstract]
AFS Securities	571,312	571,312	566,573
Recurring Basis [Member] \| Collateralized Mortgage Obligations [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	0	0	0
Recurring Basis [Member] \| Collateralized Mortgage Obligations [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	571,312	571,312	566,573
Recurring Basis [Member] \| Collateralized Mortgage Obligations [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0	0
Recurring Basis [Member] \| Other Securities [Member]
AFS securities [Abstract]
AFS Securities	19,739	19,739	20,739
Recurring Basis [Member] \| Other Securities [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	11,438	11,438	11,493
Recurring Basis [Member] \| Other Securities [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	8,301	8,301	9,246
Recurring Basis [Member] \| Other Securities [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	$ 0	$ 0	$ 0

Amount of allowance for loan losses for collateral dependent impaired loans with specific reserves.

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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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