Investments (Schedule of Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Due in one year or less, Amortized Cost	$ 136,191
Due after one year through five years, Amortized Cost	231,940
Due after five years through ten years, Amortized Cost	135,743
Due after ten years, Amortized Cost	48,113
Debt securities, available-for-sale, cost (in dollars)	605,438	$ 597,784
Due in one year or less, Fair Value	136,140
Due after one year through five years, Fair Value	231,331
Due after five years through ten years, Fair Value	136,674
Due after ten years, Fair Value	47,886
Debt Securities, Fair Value	605,333	597,457
Mortgage Backed [Member]
Schedule of Investments [Line Items]
Debt securities, available-for-sale, cost (in dollars)	53,451
Debt Securities, Fair Value	$ 53,302	$ 59,469