Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total fixed maturity securities, available-for-sale	$ 1,813,471	$ 1,433,626
Equity securities	79,896	80,735
Recurring basis | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities	308
Common stock | Recurring basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities	14,320	17,988
Common stock | Recurring basis | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities	$ 0	$ 43	$ 44
Market approach | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total fixed maturity securities, available-for-sale				$ 4,200