Investments - Maturity Table (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,535,568	$ 1,986,957
Estimated Fair Value	2,517,956	$ 1,996,634
Maturity 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	850,032
Estimated Fair Value	850,326
Maturity 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	162,617
Estimated Fair Value	162,003
Maturity 2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	398,583
Estimated Fair Value	394,941
Maturity 2026
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	547,712
Estimated Fair Value	540,382
Maturity 2038
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	74
Estimated Fair Value	79
Maturity 2039
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,029
Estimated Fair Value	1,120
Maturity 2042
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,183
Estimated Fair Value	3,175
Maturity 2043
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,599
Estimated Fair Value	5,797
Maturity 2044
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,620
Estimated Fair Value	7,881
Maturity 2045
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,764
Estimated Fair Value	6,968
Maturity 2046
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,629
Estimated Fair Value	10,818
Maturity 2047
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	12,611
Estimated Fair Value	12,822
Maturity 2048
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,961
Estimated Fair Value	3,025
Maturity 2049
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19,828
Estimated Fair Value	20,458
Maturity 2050
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	134,707
Estimated Fair Value	131,063
Maturity 2051
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	178,250
Estimated Fair Value	174,853
Maturity 2053
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	141,251
Estimated Fair Value	140,260
Maturity 2054
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	52,118
Estimated Fair Value	$ 51,985