Investments (Schedule of Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Due in one year or less	$ 255,768
Amortized Cost, Due after one year through five years	200,343
Amortized Cost, Due after five years through ten years	28,632
Amortized Cost, Amortized Cost Due after ten years	12,665
Debt Maturities, Amortized Cost	502,167	$ 569,498
Fair Value, Due in one year or less	257,246
Fair Value, Due after one year through five years	203,625
Fair Value, Due after five years through ten years	28,363
Fair Value, Due after ten years	13,202
Fair Value	507,279	$ 574,279
Mortgage Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Maturities, Amortized Cost	4,759
Fair Value	$ 4,843