| **Fair Value Measurements - Level 3 unobservable inputs (Details 3) - Recurring basis - USD ($) $ in Thousands**                                  | 9 Months Ended | 12 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------------------------------|----------------|-----------------|
||
| **Significant unobservable inputs used during the valuation of assets categorized within Level 3 of the recurring fair value measurements table** |           |            |
| Embedded derivatives - GLWB                                                                                                                       | $ 31,277       | $ 11,257        |
| Level 3                                                                                                                                           |           |            |
| **Significant unobservable inputs used during the valuation of assets categorized within Level 3 of the recurring fair value measurements table** |           |            |
| Embedded derivatives - GLWB                                                                                                                       | $ 31,277       | $ 11,257        |
| Level 3 | Internal model pricing | Minimum                                                                                                        |           |            |
| **Unobservable Input**                                                                                                                            |           |            |
| Equity Volatility                                                                                                                                 | 15.00%         | 15.00%          |
| Swap Curve                                                                                                                                        | 0.50%          | 0.75%           |
| Lapse Rate                                                                                                                                        | 1.00%          | 1.00%           |
| Level 3 | Internal model pricing | Maximum                                                                                                        |           |            |
| **Unobservable Input**                                                                                                                            |           |            |
| Equity Volatility                                                                                                                                 | 28.00%         | 28.00%          |
| Swap Curve                                                                                                                                        | 2.50%          | 3.00%           |
| Lapse Rate                                                                                                                                        | 15.00%         | 15.00%          |
| Derivative Financial Instruments, Liabilities | Level 3 | Internal model pricing                                                                  |           |            |
| **Significant unobservable inputs used during the valuation of assets categorized within Level 3 of the recurring fair value measurements table** |           |            |
| Embedded derivatives - GLWB                                                                                                                       | $ 31,277       | $ 11,257        |

| X                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Equity Volatility
+ References
No definition available.
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| X                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Lapse Rate
+ References
No definition available.
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| X                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Swap Curve
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as a liability.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624163-113959
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| X                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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