Investments - Maturity Table (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,524,634	$ 2,554,332
Estimated Fair Value	2,315,978	$ 2,342,089
2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	25,000
Estimated Fair Value	24,767
2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	699,111
Estimated Fair Value	677,812
2025
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	298,564
Estimated Fair Value	285,252
2026
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	548,563
Estimated Fair Value	492,182
2027
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	98,511
Estimated Fair Value	92,979
2038
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	69
Estimated Fair Value	68
2039
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	663
Estimated Fair Value	622
2042
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,439
Estimated Fair Value	2,008
2043
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,209
Estimated Fair Value	3,573
2044
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,945
Estimated Fair Value	4,302
2045
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,163
Estimated Fair Value	4,337
2046
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,841
Estimated Fair Value	6,540
2047
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,917
Estimated Fair Value	6,658
2048
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,032
Estimated Fair Value	1,790
2049
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	15,899
Estimated Fair Value	13,366
2050
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	109,845
Estimated Fair Value	82,601
2051
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	156,133
Estimated Fair Value	116,543
2052
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	54,219
Estimated Fair Value	44,328
2053
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	163,617
Estimated Fair Value	150,202
2054
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	75,509
Estimated Fair Value	67,142
2055
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	90,148
Estimated Fair Value	86,125
2056
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	105,584
Estimated Fair Value	104,292
2058
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	48,653
Estimated Fair Value	$ 48,489