Fair Value Measurements and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 1 to Level 2	$ 800	$ 0
Transfers from Level 2 to Level 1	4,000	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
AFS securities [Abstract]
AFS Securities	1,265,912	1,255,925
Equity securities	21,992	0
Trading securities	0	11,467
Liabilities [Abstract]
Collateral dependent impaired loans	100	100
Collateral dependent impaired loans, specific reserves	$ 100	100
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	$ 138,459	108,899
State & Municipal [Member]
AFS securities [Abstract]
AFS Securities	39,386	41,956
Equity Securities [Member]
AFS securities [Abstract]
AFS Securities		14,149
Recurring Basis [Member]
AFS securities [Abstract]
AFS Securities	1,265,912	1,255,925
Equity securities	21,992
Trading securities		11,467
Derivatives	13,414	3,732
Total	1,301,318	1,271,124
Liabilities [Abstract]
Derivatives	9,514	324
Total	9,514	324
Recurring Basis [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities	0	5,845
Equity securities	17,010
Trading securities		11,467
Derivatives	0	0
Total	17,010	17,312
Liabilities [Abstract]
Derivatives	0	0
Total	0	0
Recurring Basis [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities	1,265,912	1,250,080
Equity securities	4,982
Trading securities		0
Derivatives	13,414	3,732
Total	1,284,308	1,253,812
Liabilities [Abstract]
Derivatives	9,514	324
Total	9,514	324
Recurring Basis [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	0	0
Equity securities	0
Trading securities		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	138,459	108,899
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	138,459	108,899
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	39,386	41,956
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	39,386	41,956
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	544,031	554,927
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	544,031	554,927
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	544,036	535,994
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	544,036	535,994
Recurring Basis [Member] \| Collateralized Mortgage Obligations [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities	$ 0	0
Recurring Basis [Member] \| Equity Securities [Member]
AFS securities [Abstract]
AFS Securities		14,149
Recurring Basis [Member] \| Equity Securities [Member] \| Level 1 [Member]
AFS securities [Abstract]
AFS Securities		5,845
Recurring Basis [Member] \| Equity Securities [Member] \| Level 2 [Member]
AFS securities [Abstract]
AFS Securities		8,304
Recurring Basis [Member] \| Equity Securities [Member] \| Level 3 [Member]
AFS securities [Abstract]
AFS Securities		$ 0

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

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The percentage of liquidation expenses estimated with liquidating impaired collateral.

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Amount of impaired loans considered to be collateral dependent.

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Amount of specific reserves for impaired loans considered to be collateral dependent.

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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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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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