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Investment Information - Allowance for expected credit losses (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items] |  |  |  |  |
Additions for current-period provision for expected credit losses |  | $ 3,597 |  | $ 0 | $ 0
Fixed maturities |  |  |  |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items] |  |  |  |  |
Balance at beginning of period |  | 0 |  |  |
Cumulative effect of accounting change | [1],[2] | 634 |  |  |
Additions for current-period provision for expected credit losses |  | 10,653 |  |  |
Additions (reductions) for previously recognized expected credit losses |  | (7,030) |  |  |
Reductions due to disposals |  | (1,860) |  |  |
Write-offs charged against the allowance |  | 0 |  |  |
Balance at end of period |  | 2,397 |  | 0 |
Fixed maturities | Stuctured securities |  |  |  |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items] |  |  |  |  |
Balance at end of period | [3] | 1,090 |  |  |
Fixed maturities | Municipal bonds |  |  |  |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items] |  |  |  |  |
Balance at beginning of period |  | 0 |  |  |
Cumulative effect of accounting change | [1],[2] | 0 |  |  |
Additions for current-period provision for expected credit losses |  | 67 |  |  |
Additions (reductions) for previously recognized expected credit losses |  | 6 |  |  |
Reductions due to disposals |  | (62) |  |  |
Write-offs charged against the allowance |  | 0 |  |  |
Balance at end of period |  | 11 | [3] | 0 |
Fixed maturities | Corporate bonds |  |  |  |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items] |  |  |  |  |
Balance at beginning of period |  | 0 |  |  |
Cumulative effect of accounting change | [1],[2] | 117 |  |  |
Additions for current-period provision for expected credit losses |  | 7,644 |  |  |
Additions (reductions) for previously recognized expected credit losses |  | (5,638) |  |  |
Reductions due to disposals |  | (1,227) |  |  |
Write-offs charged against the allowance |  | 0 |  |  |
Balance at end of period |  | 896 |  | 0 |
Fixed maturities | Structured securities |  |  |  |  |
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items] |  |  |  |  |
Balance at beginning of period | [4] | 0 |  |  |
Cumulative effect of accounting change | [1],[2],[4] | 517 |  |  |
Additions for current-period provision for expected credit losses | [4] | 2,942 |  |  |
Additions (reductions) for previously recognized expected credit losses | [4] | (1,398) |  |  |
Reductions due to disposals | [4] | (571) |  |  |
Write-offs charged against the allowance | [4] | 0 |  |  |
Balance at end of period | [4] | $ 1,490 |  | $ 0 |
[1] | Adoption of ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326)”
[2] | Adoption of ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326)”
[3] | Effective January 1, 2020, the Company adopted ASU 2016-13 and as a result any credit impairment losses on the Company’s available-for-sale investments are recorded as an allowance, subject to reversal.
[4] | Includes asset backed securities, mortgage backed securities and commercial mortgage backed securities.

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- Definition Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922900-210455 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 9 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922900-210455 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aaa) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454 + Details
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- Definition Amount of expense for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), for which no credit loss was previously recorded. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922900-210455 + Details
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- Definition Amount of expense (reversal of expense) for allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), not intended to be sold and not more likely than not will be required to sell before recovery of amortized cost basis, with previously recorded allowance. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 9 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922900-210455 + Details
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