Investments - Unrealized Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Cost or amortized Cost
Total Cost or Amortized Cost	$ 2,032,827	$ 2,402,211
Fair value
Total Fair Value	1,872,031	2,187,815
Unrealized Loss
Total Unrealized Loss	$ (160,796)	$ (214,396)
Percent to Total	100.00%
NAIC Rating 1 | AAA/AA/A | Aaa/Aa/A
Cost or amortized Cost
Total Cost or Amortized Cost	$ 1,660,081
Fair value
Total Fair Value	1,517,662
Unrealized Loss
Total Unrealized Loss	$ (142,419)
Percent to Total	88.60%
NAIC Rating 2 | BBB | Baa
Cost or amortized Cost
Total Cost or Amortized Cost	$ 321,619
Fair value
Total Fair Value	305,816
Unrealized Loss
Total Unrealized Loss	$ (15,803)
Percent to Total	9.80%
NAIC Rating 3 | BB | Ba
Cost or amortized Cost
Total Cost or Amortized Cost	$ 25,671
Fair value
Total Fair Value	24,974
Unrealized Loss
Total Unrealized Loss	$ (697)
Percent to Total	0.40%
NAIC Rating 4 | B | B
Cost or amortized Cost
Total Cost or Amortized Cost	$ 21,703
Fair value
Total Fair Value	20,562
Unrealized Loss
Total Unrealized Loss	$ (1,141)
Percent to Total	0.70%
NAIC Rating 5 | CCC | Caa
Cost or amortized Cost
Total Cost or Amortized Cost	$ 2,933
Fair value
Total Fair Value	2,610
Unrealized Loss
Total Unrealized Loss	$ (323)
Percent to Total	0.20%
NAIC Rating 6 | CC Or Lower | Ca or lower
Cost or amortized Cost
Total Cost or Amortized Cost	$ 820
Fair value
Total Fair Value	407
Unrealized Loss
Total Unrealized Loss	$ (413)
Percent to Total	0.30%