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Note 4 - Fair Value of Financial Instruments Assets Measured at Fair Value by Hierarchy Level (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Other Investments |  | $ 3,585,000 |  |  | $ 3,585,000 |  |  | $ 334,000 |
Reinvested cash collateral held under securities lending agreements |  | 31,800,000 |  |  | 31,800,000 |  |  | 19,357,000 |
Loaned securities |  | 34,364,000 |  |  | 34,364,000 |  |  | 27,964,000 |
Carrying (Reported) Amount, Fair Value Disclosure |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Other Investments |  | 3,600,000 |  |  | 3,600,000 |  |  |  |
Cost Method Investments | [1] | 0 |  |  | 0 |  |  | 334,000 |
Fair Value, Measurements, Recurring |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 5,059,014,000 | [2],[3] |  | 5,059,014,000 | [2],[3] |  | 4,671,572,000 | [4],[5]
Total Assets at Fair Value |  | 5,059,014,000 | [3] |  | 5,059,014,000 | [3] |  | 4,671,572,000 | [5]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount |  | 0 |  | $ 0 | 0 |  | $ 0 |  |
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount |  | 0 |  | 0 | 0 |  | 0 |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net |  | 0 |  | 0 | 0 |  | 0 |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfers, Net |  | 0 |  | $ 0 | 0 |  | $ 0 |  |
Fair Value, Measurements, Recurring | US government and agency securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 256,052,000 |  |  | 256,052,000 |  |  | 132,992,000 |
Fair Value, Measurements, Recurring | State and municipal obligations |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 345,029,000 |  |  | 345,029,000 |  |  | 386,111,000 |
Fair Value, Measurements, Recurring | Money market instruments |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 156,396,000 |  |  | 156,396,000 |  |  | 213,357,000 |
Fair Value, Measurements, Recurring | Corporate bonds and notes |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 2,480,097,000 |  |  | 2,480,097,000 |  |  | 2,304,017,000 |
Fair Value, Measurements, Recurring | RMBS |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 272,125,000 |  |  | 272,125,000 |  |  | 216,749,000 |
Fair Value, Measurements, Recurring | CMBS |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 576,829,000 |  |  | 576,829,000 |  |  | 503,955,000 |
Fair Value, Measurements, Recurring | Other ABS |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 674,509,000 |  |  | 674,509,000 |  |  | 676,158,000 |
Fair Value, Measurements, Recurring | Foreign government securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  |  |  |  |  |  |  | 36,448,000 |
Fair Value, Measurements, Recurring | Equity securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 148,712,000 |  |  | 148,712,000 |  |  | 176,065,000 |
Fair Value, Measurements, Recurring | Other investments |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 149,265,000 | [6] |  | 149,265,000 | [6] |  | 25,720,000 | [7]
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 536,101,000 | [2] |  | 536,101,000 | [2] |  | 513,531,000 | [4]
Total Assets at Fair Value |  | 536,101,000 |  |  | 536,101,000 |  |  | 513,531,000 |
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | US government and agency securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 234,507,000 |  |  | 234,507,000 |  |  | 124,969,000 |
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | State and municipal obligations |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 0 |  |  | 0 |  |  | 0 |
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Money market instruments |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 156,396,000 |  |  | 156,396,000 |  |  | 213,357,000 |
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Corporate bonds and notes |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 0 |  |  | 0 |  |  | 0 |
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | RMBS |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 0 |  |  | 0 |  |  | 0 |
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | CMBS |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 0 |  |  | 0 |  |  | 0 |
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Other ABS |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 0 |  |  | 0 |  |  | 0 |
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Foreign government securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  |  |  |  |  |  |  | 0 |
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Equity securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 145,198,000 |  |  | 145,198,000 |  |  | 175,205,000 |
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Other investments |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 0 | [6] |  | 0 | [6] |  | 0 | [7]
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 4,522,913,000 | [2] |  | 4,522,913,000 | [2] |  | 4,158,041,000 | [4]
Total Assets at Fair Value |  | 4,522,913,000 |  |  | 4,522,913,000 |  |  | 4,158,041,000 |
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | US government and agency securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 21,545,000 |  |  | 21,545,000 |  |  | 8,023,000 |
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | State and municipal obligations |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 345,029,000 |  |  | 345,029,000 |  |  | 386,111,000 |
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Money market instruments |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 0 |  |  | 0 |  |  | 0 |
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Corporate bonds and notes |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 2,480,097,000 |  |  | 2,480,097,000 |  |  | 2,304,017,000 |
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | RMBS |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 272,125,000 |  |  | 272,125,000 |  |  | 216,749,000 |
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | CMBS |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 576,829,000 |  |  | 576,829,000 |  |  | 503,955,000 |
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Other ABS |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 674,509,000 |  |  | 674,509,000 |  |  | 676,158,000 |
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Foreign government securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  |  |  |  |  |  |  | 36,448,000 |
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Equity securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 3,514,000 |  |  | 3,514,000 |  |  | 860,000 |
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Other investments |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Investments at Fair Value |  | 149,265,000 | [6] |  | 149,265,000 | [6] |  | 25,720,000 | [7]
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Total Assets at Fair Value |  | 0 |  |  | 0 |  |  | 0 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value |  | 0 |  |  | 0 |  |  | 0 |
Securities Financing Transaction, Fair Value |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Reinvested cash collateral held under securities lending agreements | [8] | 31,799,000 |  |  | 31,799,000 |  |  | 19,357,000 |
Loaned securities | [9] | 34,364,000 |  |  | 34,364,000 |  |  | 27,964,000 |
Securities Financing Transaction, Fair Value | Corporate bonds and notes |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Loaned securities | [9] | 7,427,000 |  |  | 7,427,000 |  |  | 13,862,000 |
Securities Financing Transaction, Fair Value | Foreign government securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Loaned securities | [9] | 0 |  |  | 0 |  |  | 867,000 |
Securities Financing Transaction, Fair Value | Equity securities |  |  |  |  |  |  |  |  |
Fair Value by Hierarchy Level [Line Items] |  |  |  |  |  |  |  |  |
Loaned securities | [9] | $ 26,847,000 |  |  | $ 26,847,000 |  |  | $ 13,235,000 |
[1] | As a result of implementing the update to the standard for the accounting of financial instruments effective January 1, 2018, other invested assets are no longer carried at amortized cost.
[2] | Does not include certain other invested assets ($3.6 million), primarily invested in limited partnership investments valued using the net asset value as a practical expedient. Includes cash collateral held under securities lending agreements ($31.8 million) reinvested in money market instruments.
[3] | Includes $34.4 million of securities loaned to third-party Borrowers under securities lending agreements, classified as other assets in our consolidated balance sheets. See Note 5 for more information.
[4] | Does not include certain other invested assets ($0.3 million), primarily invested in limited partnerships, accounted for as cost-method investments and not measured at fair value. Includes cash collateral held under securities lending agreements ($19.4 million) reinvested in money market instruments.
[5] | Includes $28.0 million of securities loaned to third-party Borrowers under securities lending agreements, classified as other assets in our consolidated balance sheets. See Note 5 for more information.
[6] | Comprising short-term certificates of deposit and commercial paper.
[7] | Comprising short-term certificates of deposit and commercial paper.
[8] | All cash collateral received has been reinvested in accordance with the securities lending agreements and is included in short-term investments in our condensed consolidated balance sheets. Amounts payable on the return of cash collateral under securities lending agreements are included within other liabilities in our condensed consolidated balance sheets.
[9] | Our securities loaned under securities lending agreements are reported at fair value within other assets in our condensed consolidated balance sheets. All of our securities lending agreements are classified as overnight and revolving. None of the amounts are subject to offsetting.

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- Definition Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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