Investments - Net Realized and Unrealized Gains (Losses) on Investments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Gain (Loss) on Securities [Line Items]
Other investments, gross gains		$ 98
Other investments, gross losses		0
Other investments, net		98
Net realized gains (losses) on investment, gross gains	$ 4,663	13,604	$ 24,761	$ 41,615
Net realized gains (losses) on investment, gross losses	(530)	(904)	(715)	(15,930)
Net realized gains (losses) on investment, net	4,133	12,700	24,046	25,685
Proceeds from sales of fixed maturities classified as available-for-sale	71,857	136,347	477,358	845,962
Deferred income tax	(114)		(114)		$ (96)
Net unrealized gains, net of deferred income tax	28,938		28,938		21,996
Change, net of deferred income tax			6,942		81,758
Fixed maturities
Gain (Loss) on Securities [Line Items]
AFS fixed maturities, gross gains	3,948	13,506	23,939	41,366
AFS fixed maturities, gross losses	0	(904)	(1)	(15,785)
AFS fixed maturities, net	3,948	$ 12,602	23,938	25,581
Other Debt Obligations
Gain (Loss) on Securities [Line Items]
Other investments, gross gains	715		822	249
Other investments, gross losses	(530)		(714)	(145)
Other investments, net	185		108	$ 104
Available-for-sale securities | Fixed maturities
Gain (Loss) on Securities [Line Items]
Fixed maturities	$ 29,052		$ 29,052		$ 22,092