Investments (Schedule of Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Due in one year or less	$ 212,895
Amortized Cost, Due after one year through five years	319,397
Amortized Cost, Due after five years through ten years	38,117
Amortized Cost, Amortized Cost Due after ten years	19,196
Debt Maturities, Amortized Cost	597,170	$ 569,498
Fair Value, Due in one year or less	213,273
Fair Value, Due after one year through five years	314,222
Fair Value, Due after five years through ten years	35,813
Fair Value, Due after ten years	18,512
Fair Value	589,383	$ 574,279
Mortgage Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Maturities, Amortized Cost	7,565
Fair Value	$ 7,563