Investments - Unrealized Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Cost or amortized Cost
Total Cost or Amortized Cost	$ 2,584,921	$ 2,402,211
Fair value
Total Fair Value	2,357,051	2,187,815
Unrealized Loss
Total Unrealized Loss	$ (227,870)	$ (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	$ 2,137,898
Fair value
Total Fair Value	1,941,077
Unrealized Loss
Total Unrealized Loss	$ (196,821)
Percent to Total	86.40%
NAIC Rating 2 | BBB | Baa
Cost or amortized Cost
Total Cost or Amortized Cost	$ 397,220
Fair value
Total Fair Value	369,097
Unrealized Loss
Total Unrealized Loss	$ (28,123)
Percent to Total	12.30%
NAIC Rating 3 | BB | Ba
Cost or amortized Cost
Total Cost or Amortized Cost	$ 31,428
Fair value
Total Fair Value	29,952
Unrealized Loss
Total Unrealized Loss	$ (1,476)
Percent to Total	0.70%
NAIC Rating 4 | B | B
Cost or amortized Cost
Total Cost or Amortized Cost	$ 14,826
Fair value
Total Fair Value	14,073
Unrealized Loss
Total Unrealized Loss	$ (753)
Percent to Total	0.30%
NAIC Rating 5 | CCC | Caa
Cost or amortized Cost
Total Cost or Amortized Cost	$ 2,730
Fair value
Total Fair Value	2,421
Unrealized Loss
Total Unrealized Loss	$ (309)
Percent to Total	0.10%
NAIC Rating 6 | CC Or Lower | Ca or lower
Cost or amortized Cost
Total Cost or Amortized Cost	$ 819
Fair value
Total Fair Value	431
Unrealized Loss
Total Unrealized Loss	$ (388)
Percent to Total	0.20%