Investments (Schedule of Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Due in one year or less	$ 121,593
Amortized Cost, Due after one year through five years	309,542
Amortized Cost, Due after five years through ten years	94,338
Amortized Cost, Amortized Cost Due after ten years	30,282
Debt Maturities, Amortized Cost	564,602	$ 550,268
Fair Value, Due in one year or less	121,977
Fair Value, Due after one year through five years	312,076
Fair Value, Due after five years through ten years	94,489
Fair Value, Due after ten years	31,553
Total debt securities	568,831	$ 545,870
Mortgage Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Maturities, Amortized Cost	8,847
Total debt securities	$ 8,736