Investments (Schedule of Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Due in one year or less, Amortized Cost	$ 153,323
Due after one year through five years, Amortized Cost	231,340
Due after five years through ten years, Amortized Cost	143,558
Due after ten years, Amortized Cost	42,884
Debt securities, available-for-sale, cost (in dollars)	605,986	$ 597,784
Due in one year or less, Fair Value	153,486
Due after one year through five years, Fair Value	232,487
Due after five years through ten years, Fair Value	144,413
Due after ten years, Fair Value	42,915
Debt Securities, Fair Value	608,074	597,457
Mortgage Backed [Member]
Schedule of Investments [Line Items]
Debt securities, available-for-sale, cost (in dollars)	34,881
Debt Securities, Fair Value	$ 34,773	$ 59,469