Investments (Schedule of Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Due in one year or less, Amortized Cost	$ 163,460
Due after one year through five years, Amortized Cost	254,385
Due after five years through ten years, Amortized Cost	134,207
Due after ten years, Amortized Cost	45,376
Debt securities, available-for-sale, cost (in dollars)	616,885	$ 597,784
Due in one year or less, Fair Value	163,697
Due after one year through five years, Fair Value	255,618
Due after five years through ten years, Fair Value	134,902
Due after ten years, Fair Value	44,664
Debt Securities, Fair Value	618,234	597,457
Mortgage Backed [Member]
Schedule of Investments [Line Items]
Debt securities, available-for-sale, cost (in dollars)	19,457
Debt Securities, Fair Value	$ 19,353	$ 59,469