Investments (Schedule of Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Due in one year or less	$ 117,306
Amortized Cost, Due after one year through five years	276,397
Amortized Cost, Due after five years through ten years	96,047
Amortized Cost, Amortized Cost Due after ten years	30,867
Debt Maturities, Amortized Cost	530,516	$ 550,268
Fair Value, Due in one year or less	117,293
Fair Value, Due after one year through five years	278,718
Fair Value, Due after five years through ten years	95,636
Fair Value, Due after ten years	31,645
Total debt securities	533,148	$ 545,870
Mortgage Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Debt Maturities, Amortized Cost	9,899
Total debt securities	$ 9,856