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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

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