Investments - Narrative (Details)		3 Months Ended				9 Months Ended
	Sep. 30, 2019 USD ($) issuer	Sep. 30, 2019 USD ($) issuer	Mar. 31, 2019 USD ($) security	Sep. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) loan issuer	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Gain (Loss) on Securities [Line Items]
Number of issuers | issuer	76	76				76
Total fair value	$ 232,726,000	$ 232,726,000				$ 232,726,000
Gross unrealized losses	1,763,000	1,763,000				1,763,000
Fixed maturity securities, available-for-sale	1,377,323,000	1,377,323,000				$ 1,377,323,000		$ 1,184,202,000
Number of impaired loans | loan						5
Carrying value of impaired loans	6,400,000	6,400,000				$ 6,400,000
Unpaid principal on impaired loans	12,300,000	12,300,000				12,300,000
Allowance for credit losses on impaired loans	5,900,000	5,900,000				5,900,000			$ 3,200,000
Net realized and unrealized (losses) gains on investments		(2,357,000)		$ 467,000		331,000	$ (407,000)
Average recorded investment in impaired bank loans						3,200,000	2,600,000
Investment income during period loans were impaired						23,000	125,000
Net realized gain (loss) on changes in fair value of impaired bank loans		(5,900,000)		$ 42,000		(7,700,000)	$ (851,000)
Carrying value of collateralized loan obligation held	3,400,000	3,400,000				3,400,000
Fixed maturity securities
Gain (Loss) on Securities [Line Items]
Total fair value								852,854,000
Gross unrealized losses								21,267,000
Fixed maturity securities, available-for-sale	$ 1,377,323,000	$ 1,377,323,000				$ 1,377,323,000		$ 1,184,202,000
Number of impaired fixed maturities | security			3
Impairment losses			$ 271,000
Bank Loan Portfolio
Gain (Loss) on Securities [Line Items]
Number of issuers | issuer	4	4				4
Loans from Issuer Experiencing Liquidity Concerns
Gain (Loss) on Securities [Line Items]
Number of issuers | issuer	1	1				1
Number of impaired loans | loan						2
Allowance for credit losses on impaired loans	$ 4,200,000	$ 4,200,000				$ 4,200,000
Puerto Rico loan
Gain (Loss) on Securities [Line Items]
Carrying value of impaired loans									0
Unpaid principal on impaired loans									$ 807,000
Net realized and unrealized (losses) gains on investments					$ 807,000
BBB- or better | Fixed maturity securities
Gain (Loss) on Securities [Line Items]
Percentage of available for sale securities	99.60%	99.60%				99.60%
Below BBB-
Gain (Loss) on Securities [Line Items]
Fixed maturity securities, available-for-sale	$ 5,300,000	$ 5,300,000				$ 5,300,000
Aggregate net unrealized gain (loss)	$ 79,000