Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total fixed maturity securities, available-for-sale		$ 1,332,042		$ 1,184,202
Equity securities		87,528		78,385
Principal payment received		64,905	$ 81,138
Market approach | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total fixed maturity securities, available-for-sale				4,200
Principal payment received	$ 456
Nonrecurring basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired bank loan participations held for investment		3,359		0
Nonrecurring basis | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired bank loan participations held for investment		3,359		0
Nonrecurring basis | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Impaired bank loan participations held for investment		0		0
Common stock | Recurring basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities		20,273		17,645
Common stock | Recurring basis | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities		3,099		214
Common stock | Recurring basis | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities		$ 1,761		$ 757