Fair Value of Financial Instruments - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Thousands	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed maturity securities	$ 6,021,983	$ 5,791,676
Equity securities at fair value	90,338	101,864
Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed maturity securities	1,805,550	1,686,203
Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed maturity securities	1,862,440	1,581,424
Other asset-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed maturity securities	1,216,588	1,295,492
Government mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed maturity securities	718,974	$ 724,319
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities at fair value	115
Derivatives embedded in fixed indexed annuity products	$ 93,619
Level 3 | discounted cash flow | lapse rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products, measurement input	0.0525
Level 3 | discounted cash flow | mortality multiplier | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products, measurement input	0.6100
Level 3 | discounted cash flow | option budget | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products, measurement input	0.0100
Level 3 | discounted cash flow | option budget | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products, measurement input	0.0250
Level 3 | discounted cash flow | Non-Performance Adjustment | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives embedded in fixed indexed annuity products, measurement input	0.0500
Level 3 | Black Scholes | equity value | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities, measurement input	43.27
Level 3 | Black Scholes | equity value | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity securities, measurement input	44.53
Level 3 | Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed maturity securities	$ 73,171
Level 3 | Municipal bonds | discounted cash flow | I Spread | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0578
Level 3 | Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed maturity securities	$ 126,292
Level 3 | Corporate bonds | discounted cash flow | I Spread | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0495
Level 3 | Corporate bonds | discounted cash flow | N Spread | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0762
Level 3 | Corporate bonds | discounted cash flow | T Spread | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0378
Level 3 | Corporate bonds | market comparable | EV / TTM EBITDA (x) | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	5.11
Level 3 | Other asset-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed maturity securities	$ 175,685
Level 3 | Other asset-backed securities | discounted cash flow | N Spread | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0732
Level 3 | Other asset-backed securities | discounted cash flow | constant prepayment yield | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.200
Level 3 | Other asset-backed securities | discounted cash flow | PDI Interest Margin | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0713
Level 3 | Other asset-backed securities | discounted cash flow | SBL Interest Margin | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0450
Level 3 | Other asset-backed securities | vendor price | haircut | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.030
Level 3 | Other asset-backed securities | market comparable | EV / TTM EBITDA (x) | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	5.11
Level 3 | Government mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fixed maturity securities	$ 24,461
Level 3 | Government mortgage-backed securities | discounted cash flow | N Spread | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0109
Level 3 | Government mortgage-backed securities | discounted cash flow | constant prepayment yield | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.0100
Level 3 | Government mortgage-backed securities | discounted cash flow | Constant Default Rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0
Level 3 | Government mortgage-backed securities | vendor price | haircut | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, measurement input	0.030