Investments (Schedule of Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Due in one year or less, Amortized Cost	$ 122,350
Due after one year through five years, Amortized Cost	264,476
Due after five years through ten years, Amortized Cost	92,907
Due after ten years, Amortized Cost	31,074
Debt securities, available-for-sale, cost (in dollars)	523,745	$ 550,268
Due in one year or less, Fair Value	121,972
Due after one year through five years, Fair Value	265,022
Due after five years through ten years, Fair Value	91,964
Due after ten years, Fair Value	31,285
Debt Securities, Fair Value	522,977	545,870
Mortgage Backed [Member]
Schedule of Investments [Line Items]
Debt securities, available-for-sale, cost (in dollars)	12,938
Debt Securities, Fair Value	$ 12,734	$ 13,557