Investments, Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2020 USD ($) Secutrity	Dec. 31, 2019 USD ($) Secutrity
Available-for-sale Securities Continuous Unrealized Loss Positions [Abstract]
Number of securities, 12 months or less | Secutrity	155	88
Number of securities, Greater than 12 months | Secutrity	25	69
Number of securities, total | Secutrity	180	157
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, 12 months or less	$ 149,489	$ 108,387
Fair value, Greater than 12 months	28,495	66,860
Fair value, total	177,984	175,247
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, 12 months or less	(8,214)	(2,452)
Gross unrealized loss, Greater than 12 months	(3,493)	(1,100)
Gross unrealized loss, total	(11,707)	(3,552)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
One year or less, Fair Value	92,882
Excess of one year to five years, Fair Value	337,419
Excess of five years to ten years, Fair Value	144,672
Excess of ten years, Fair Value	22,781
Total contractual maturities, Fair Value	597,754
Asset-backed securities, Fair Value	254,183
Total, Fair Value	851,937	795,538
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
One year or less, Cost or Amortized Cost	92,080
Excess of one year to five years, Cost or Amortized Cost	324,886
Excess of five years to ten years, Cost or Amortized Cost	135,091
Excess of ten years, Cost or Amortized Cost	22,550
Total contractual maturities, Cost or Amortized Cost	574,607
Asset-backed securities, Cost or Amortized Cost	258,354
Cost or amortized cost	$ 832,961	$ 783,047