Investments - Net Investment Income (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Investments, Debt and Equity Securities [Abstract] | |||
| Investment income | $ 31,332 | $ 24,342 | $ 17,046 |
| Investment expenses | (476) | (804) | (773) |
| Net investment income | $ 30,856 | $ 23,538 | $ 16,273 |