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Note 5 - Investments Schedule of Unrealized Losses (Details) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 USD ($) security | Dec. 31, 2017 USD ($) security | Dec. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items] |  |  |
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net | $ 844 | $ (1,400) |
Continuous Loss Position Less Than Twelve Months [Abstract] |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security | 612 | 332 |
Fair value available-for-sale securities | $ 2,417,708 | $ 1,338,867 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | $ 46,167 | $ 9,827 |
Continuous Unrealized Loss Position, Twelve Months Or Greater |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security | 68 | 72 |
Fair value available-for-sale securities | $ 223,335 | $ 262,531 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ 11,699 | $ 6,607 |
Continuous Loss Position, Total |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security | 680 | 404 |
Fair value available-for-sale securities | $ 2,641,043 | $ 1,601,398 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | 57,866 | 16,434 |
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held | $ 0 | $ 0 |
US government and agency securities |  |  |
Continuous Loss Position Less Than Twelve Months [Abstract] |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security | 7 | 6 |
Fair value available-for-sale securities | $ 41,246 | $ 23,309 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | $ 1,116 | $ 129 |
Continuous Unrealized Loss Position, Twelve Months Or Greater |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security | 3 | 3 |
Fair value available-for-sale securities | $ 9,520 | $ 9,799 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ 506 | $ 238 |
Continuous Loss Position, Total |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security | 10 | 9 |
Fair value available-for-sale securities | $ 50,766 | $ 33,108 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | $ 1,622 | $ 367 |
US States and Political Subdivisions Debt Securities [Member] |  |  |
Continuous Loss Position Less Than Twelve Months [Abstract] |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security | 28 | 21 |
Fair value available-for-sale securities | $ 79,897 | $ 65,898 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | $ 1,729 | $ 699 |
Continuous Unrealized Loss Position, Twelve Months Or Greater |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security | 0 | 0 |
Fair value available-for-sale securities | $ 0 | $ 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ 0 | $ 0 |
Continuous Loss Position, Total |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security | 28 | 21 |
Fair value available-for-sale securities | $ 79,897 | $ 65,898 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | $ 1,729 | $ 699 |
Corporate bonds and notes |  |  |
Continuous Loss Position Less Than Twelve Months [Abstract] |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security | 344 | 152 |
Fair value available-for-sale securities | $ 1,348,488 | $ 672,318 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | $ 32,623 | $ 4,601 |
Continuous Unrealized Loss Position, Twelve Months Or Greater |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security | 28 | 32 |
Fair value available-for-sale securities | $ 127,265 | $ 139,105 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ 7,267 | $ 3,451 |
Continuous Loss Position, Total |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security | 372 | 184 |
Fair value available-for-sale securities | $ 1,475,753 | $ 811,423 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | $ 39,890 | $ 8,052 |
RMBS |  |  |
Continuous Loss Position Less Than Twelve Months [Abstract] |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security | 20 | 8 |
Fair value available-for-sale securities | $ 112,041 | $ 19,943 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | $ 1,606 | $ 204 |
Continuous Unrealized Loss Position, Twelve Months Or Greater |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security | 27 | 26 |
Fair value available-for-sale securities | $ 79,087 | $ 101,812 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ 3,626 | $ 2,658 |
Continuous Loss Position, Total |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security | 47 | 34 |
Fair value available-for-sale securities | $ 191,128 | $ 121,755 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | $ 5,232 | $ 2,862 |
CMBS |  |  |
Continuous Loss Position Less Than Twelve Months [Abstract] |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security | 67 | 35 |
Fair value available-for-sale securities | $ 375,353 | $ 139,353 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | $ 6,592 | $ 1,395 |
Continuous Unrealized Loss Position, Twelve Months Or Greater |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security | 5 | 4 |
Fair value available-for-sale securities | $ 2,814 | $ 3,518 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ 260 | $ 215 |
Continuous Loss Position, Total |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security | 72 | 39 |
Fair value available-for-sale securities | $ 378,167 | $ 142,871 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | $ 6,852 | $ 1,610 |
Other ABS |  |  |
Continuous Loss Position Less Than Twelve Months [Abstract] |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security | 127 | 92 |
Fair value available-for-sale securities | $ 439,883 | $ 260,864 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | $ 2,228 | $ 777 |
Continuous Unrealized Loss Position, Twelve Months Or Greater |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security | 5 | 7 |
Fair value available-for-sale securities | $ 4,649 | $ 8,297 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ 40 | $ 45 |
Continuous Loss Position, Total |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security | 132 | 99 |
Fair value available-for-sale securities | $ 444,532 | $ 269,161 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | $ 2,268 | $ 822 |
Foreign government securities |  |  |
Continuous Loss Position Less Than Twelve Months [Abstract] |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security | 19 | 5 |
Fair value available-for-sale securities | $ 20,800 | $ 7,397 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | $ 273 | $ 33 |
Continuous Unrealized Loss Position, Twelve Months Or Greater |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security | 0 | 0 |
Fair value available-for-sale securities | $ 0 | $ 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $ 0 | $ 0 |
Continuous Loss Position, Total |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security | 19 | 5 |
Fair value available-for-sale securities | $ 20,800 | $ 7,397 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | $ 273 | 33 |
Debt Securities |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net |  | $ 400 |
Equity securities |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net |  |  | $ (500)
Continuous Loss Position Less Than Twelve Months [Abstract] |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | security |  | 13 |
Fair value available-for-sale securities |  | $ 149,785 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | $ 1,989 |
Continuous Unrealized Loss Position, Twelve Months Or Greater |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security |  | 0 |
Fair value available-for-sale securities |  | $ 0 |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | $ 0 |
Continuous Loss Position, Total |  |  |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security |  | 13 |
Fair value available-for-sale securities |  | $ 149,785 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 1,989 |
Debt and Equity Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net |  | 1,000 |
Convertible Debt Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net |  | $ 500 |

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