Investments - Maturity Table (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,440,204	$ 2,535,568
Estimated Fair Value	2,341,551	$ 2,517,956
2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	194,309
Estimated Fair Value	193,447
2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	162,595
Estimated Fair Value	159,383
2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	597,268
Estimated Fair Value	577,077
2025
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	297,077
Estimated Fair Value	293,021
2026
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	547,832
Estimated Fair Value	512,323
2038
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	73
Estimated Fair Value	76
2039
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	873
Estimated Fair Value	916
2042
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,912
Estimated Fair Value	2,768
2043
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,415
Estimated Fair Value	5,336
2044
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,015
Estimated Fair Value	6,959
2045
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,158
Estimated Fair Value	6,018
2046
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,374
Estimated Fair Value	9,085
2047
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,957
Estimated Fair Value	9,751
2048
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,427
Estimated Fair Value	2,437
2049
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	18,261
Estimated Fair Value	17,902
2050
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	127,490
Estimated Fair Value	116,445
2051
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	174,646
Estimated Fair Value	159,542
2052
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	40,972
Estimated Fair Value	38,693
2053
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	132,336
Estimated Fair Value	128,621
2054
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	103,214
Estimated Fair Value	$ 101,751