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Note 2 - Investments - Security Holdings in an Unrealized Loss Position (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items] |  |
Less than 12 Months, fair value | $ 104,105 | $ 354,769
Less than 12 Months, Accumulated Loss | (2,482) | (8,726)
12 Months or Longer, fair value | 264,694 | 309,203
12 Months or Longer, Accumulated Loss | (18,523) | (28,531)
Fair value | 368,799 | 663,972
Accumulated Loss | (21,005) | (37,257)
US Government Agencies Debt Securities [Member] |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items] |  |
Less than 12 Months, fair value | 1,600 | 16,507
Less than 12 Months, Accumulated Loss | (45) | (65)
12 Months or Longer, fair value | 8,161 | 14,291
12 Months or Longer, Accumulated Loss | (234) | (584)
Fair value | 9,761 | 30,798
Accumulated Loss | (279) | (649)
US States and Political Subdivisions Debt Securities [Member] |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items] |  |
Less than 12 Months, fair value | 5,181 | 2,614
Less than 12 Months, Accumulated Loss | (541) | (419)
12 Months or Longer, fair value | 9,342 | 5,076
12 Months or Longer, Accumulated Loss | (637) | (438)
Fair value | 14,523 | 7,690
Accumulated Loss | (1,178) | (857)
Special Revenue Excluding Asset Backed Securities [Member] |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items] |  |
Less than 12 Months, fair value | 230 | 2,182
Less than 12 Months, Accumulated Loss | (7) | (426)
12 Months or Longer, fair value | 14,939 | 21,733
12 Months or Longer, Accumulated Loss | (2,118) | (3,308)
Fair value | 15,169 | 23,915
Accumulated Loss | (2,125) | (3,734)
Corporate Debt Securities and Other Debt Obligations [Member] |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items] |  |
Less than 12 Months, fair value | 61,100 | 181,179
Less than 12 Months, Accumulated Loss | (1,392) | (4,996)
12 Months or Longer, fair value | 143,594 | 176,531
12 Months or Longer, Accumulated Loss | (7,134) | (13,353)
Fair value | 204,694 | 357,710
Accumulated Loss | (8,526) | (18,349)
Asset-Backed Securities [Member] |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position [Line Items] |  |
Less than 12 Months, fair value | 35,994 | 152,287
Less than 12 Months, Accumulated Loss | (497) | (2,820)
12 Months or Longer, fair value | 88,658 | 91,572
12 Months or Longer, Accumulated Loss | (8,400) | (10,848)
Fair value | 124,652 | 243,859
Accumulated Loss | $ (8,897) | $ (13,668)

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