Investments - Schedule of Available-for-Sale Fixed Maturity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	$ 1,398,533	$ 1,199,409
Fair Value	1,433,626	1,184,202
Fixed maturity securities:
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	1,398,533	1,199,409
Gross Unrealized Gains	37,691	6,060
Gross Unrealized Losses	(2,598)	(21,267)
Fair Value	1,433,626	1,184,202
State and municipal
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	159,894	147,160
Gross Unrealized Gains	7,949	3,422
Gross Unrealized Losses	(742)	(1,287)
Fair Value	167,101	149,295
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	261,524	208,869
Gross Unrealized Gains	3,244	577
Gross Unrealized Losses	(622)	(5,337)
Fair Value	264,146	204,109
Corporate
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	611,304	534,024
Gross Unrealized Gains	21,306	1,516
Gross Unrealized Losses	(389)	(10,772)
Fair Value	632,221	524,768
Commercial mortgage and asset-backed
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	249,309	199,528
Gross Unrealized Gains	3,954	310
Gross Unrealized Losses	(806)	(2,813)
Fair Value	252,457	197,025
U.S. Treasury securities and obligations guaranteed by the U.S. government
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	114,477	107,803
Gross Unrealized Gains	1,229	235
Gross Unrealized Losses	(39)	(845)
Fair Value	115,667	107,193
Redeemable preferred stock
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	2,025	2,025
Gross Unrealized Gains	9	0
Gross Unrealized Losses	0	(213)
Fair Value	$ 2,034	$ 1,812