Investments - Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
AFS fixed maturities, Amortized cost
Due in one year or less	$ 161,459
Due after one year through five years	445,698
Due after five years through ten years	127,632
Total before securities without single maturities, Amortized cost	734,789
Original or amortized cost	1,258,915	$ 1,813,426
AFS fixed maturities, Fair value
Due in one year or less	160,918
Due after one year through five years	459,737
Due after five years through ten years	131,972
Total before securities without single maturities, Fair value	752,627
Total AFS fixed maturities, Fair value	1,287,967	1,835,518
U.S. agency bonds – mortgage-backed
AFS fixed maturities, Amortized cost
Amortized cost of securities without single maturities	339,144
Original or amortized cost	339,144	533,296
AFS fixed maturities, Fair value
Fair value of securities without single maturities	350,350
Total AFS fixed maturities, Fair value	350,350	538,722
Asset-backed securities
AFS fixed maturities, Amortized cost
Amortized cost of securities without single maturities	184,982
Original or amortized cost	184,982	187,881
AFS fixed maturities, Fair value
Fair value of securities without single maturities	184,990
Total AFS fixed maturities, Fair value	$ 184,990	$ 188,170