Investments - Unrealized Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Cost or amortized Cost
Total Cost or Amortized Cost	$ 2,731,357	$ 2,402,211
Fair value
Total Fair Value	2,495,691	2,187,815
Unrealized Loss
Total Unrealized Loss	$ (235,666)	$ (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	$ 2,292,580
Fair value
Total Fair Value	2,086,894
Unrealized Loss
Total Unrealized Loss	$ (205,686)
Percent to Total	87.30%
NAIC Rating 2 | BBB | Baa
Cost or amortized Cost
Total Cost or Amortized Cost	$ 388,103
Fair value
Total Fair Value	361,830
Unrealized Loss
Total Unrealized Loss	$ (26,273)
Percent to Total	11.10%
NAIC Rating 3 | BB | Ba
Cost or amortized Cost
Total Cost or Amortized Cost	$ 30,171
Fair value
Total Fair Value	28,674
Unrealized Loss
Total Unrealized Loss	$ (1,497)
Percent to Total	0.60%
NAIC Rating 4 | B | B
Cost or amortized Cost
Total Cost or Amortized Cost	$ 16,562
Fair value
Total Fair Value	15,259
Unrealized Loss
Total Unrealized Loss	$ (1,303)
Percent to Total	0.60%
NAIC Rating 5 | CCC | Caa
Cost or amortized Cost
Total Cost or Amortized Cost	$ 3,121
Fair value
Total Fair Value	2,646
Unrealized Loss
Total Unrealized Loss	$ (475)
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	388
Unrealized Loss
Total Unrealized Loss	$ (432)
Percent to Total	0.20%