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Reinsurance - Narrative (Details) - USD ($) |  | 3 Months Ended | 6 Months Ended
--- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Effects of Reinsurance [Line Items] |  |  |  |  |
Ceded |  | $ 41,096,000 | $ 21,378,000 | $ 71,820,000 | $ 54,643,000
Quota Share Reinsurance Agreement, 2019 |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |
Contingent termination fee |  |  |  | $ 0 |
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent) |  |  |  | 90.00% |
Quota share for all policies covered (as a percent) |  |  |  | 30.00% |
Cede rate, option 1 (as a percent) |  |  |  | 25.00% |
Cede rate, option 2 (as a percent) |  |  |  | 20.00% |
Ceding commission, percentage (as a percent) |  |  |  | 20.00% |
Loss ratio threshold for profit commissions (as a percent) |  |  |  | 62.00% |
Quota Share Reinsurance Agreement, 2015 |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |
Contingent termination fee | $ 0 | 6,800,000 |  |  |
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent) |  |  |  | 90.00% |
Quota share for all policies covered (as a percent) | 15.00% |  |  | 30.00% |
Loss ratio threshold for profit commissions (as a percent) | 68.00% |  |  |  |
Excess of Loss Reinsurance Agreement, Home Re |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |
Ceded |  | $ 4,500,000 |  | $ 7,000,000.0 |

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