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Note 6 - Investments in Affordable Housing and Alternative Energy Partnerships (Details Textual) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Number Of Limited Partnerships In Housing Investments | 8 | 8 |
Increase in Total Assets and Liabilities from Consolidating Affordable Housing Equity Interest |  | $ 23.6 | $ 23.7
Low income Housing Tax Credit Investments, Pretax Write-down | $ 2.6 | 2.6 |
Affordable Housing Limited Partnerships [Member] | Domestic Tax Authority [Member] |  |  |
Remaining and Future Available Tax Credit | 190.6 | 190.6 |
Affordable Housing Limited Partnerships [Member] | State and Local Jurisdiction [Member] |  |  |
Remaining and Future Available Tax Credit | $ 2.7 | $ 2.7 |

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- Definition The amount pretax write-down of low income housing tax credit investment. + References No definition available. + Details
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