Investments (Schedule of Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Due in one year or less	$ 211,915
Amortized Cost, Due after one year through five years	281,761
Amortized Cost, Due after five years through ten years	36,751
Amortized Cost, Amortized Cost Due after ten years	14,715
Debt Maturities, Amortized Cost	552,266	$ 569,498
Fair Value, Due in one year or less	213,229
Fair Value, Due after one year through five years	282,740
Fair Value, Due after five years through ten years	34,845
Fair Value, Due after ten years	15,247
Fair Value	553,322	$ 574,279
Mortgage Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Maturities, Amortized Cost	7,124
Fair Value	$ 7,261