Investments - Maturity Table (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 485,756	$ 182,325
Estimated Fair Value	487,669	$ 176,245
Maturity 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	77,240
Estimated Fair Value	77,385
Maturity 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	138,157
Estimated Fair Value	138,640
Maturity 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	34,997
Estimated Fair Value	34,983
Maturity 2038
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	176
Estimated Fair Value	191
Maturity 2039
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,597
Estimated Fair Value	2,778
Maturity 2042
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,196
Estimated Fair Value	7,050
Maturity 2043
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	11,661
Estimated Fair Value	11,813
Maturity 2044
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17,300
Estimated Fair Value	17,487
Maturity 2045
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	18,280
Estimated Fair Value	18,332
Maturity 2046
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	28,892
Estimated Fair Value	28,822
Maturity 2047
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	45,411
Estimated Fair Value	45,353
Maturity 2048
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	12,154
Estimated Fair Value	12,478
Maturity 2049
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	91,695
Estimated Fair Value	$ 92,357