Investments, Continuous Unrealized Loss Position (Details) $ in Thousands	Jun. 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	149	88
Number of securities, Greater than 12 months | Secutrity	23	69
Number of securities, total | Secutrity	172	157
Available-for-sale Securities Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair value, 12 months or less	$ 130,567	$ 108,387
Fair value, Greater than 12 months	25,739	66,860
Fair value, total	156,306	175,247
Available-for-sale Securities Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross unrealized loss, 12 months or less	(14,097)	(2,452)
Gross unrealized loss, Greater than 12 months	(3,936)	(1,100)
Gross unrealized loss, total	(18,033)	(3,552)
Available-for-sale Securities Debt Maturities Fair Value [Abstract]
One year or less, Fair Value	96,464
Excess of one year to five years, Fair Value	319,395
Excess of five years to ten years, Fair Value	132,463
Excess of ten years, Fair Value	15,781
Total contractual maturities, Fair Value	564,103
Asset-backed securities, Fair Value	247,898
Total, Fair Value	812,001	795,538
Available-for-sale Securities Debt Maturities Amortized Cost Basis [Abstract]
One year or less, Cost or Amortized Cost	95,568
Excess of one year to five years, Cost or Amortized Cost	306,894
Excess of five years to ten years, Cost or Amortized Cost	124,972
Excess of ten years, Cost or Amortized Cost	15,805
Total contractual maturities, Cost or Amortized Cost	543,239
Asset-backed securities, Cost or Amortized Cost	257,280
Cost or amortized cost	$ 800,519	$ 783,047