Securities (Schedule of Contractual Maturities of Investment Securities Available for Sale) (Details) $ in Thousands	Sep. 30, 2017 USD ($)
Available-for-sale Securities [Abstract]
Due within one year, Amortized Cost	$ 108,477
Due after one year through five years, Amortized Cost	506,439
Due after five years through ten years, Amortized Cost	672,288
Due after ten years, Amortized Cost	922,847
No stated maturity date, Amortized Cost Basis	5,284
Total investment securities available-for-sale, Amortized Cost	2,215,335
Due within one year, Fair Value	108,462
Due after one year through five years, Fair Value	509,784
Due after five years through ten years, Fair Value	671,188
Due after ten years, Fair Value	913,325
No stated maturity date, Fair Value	5,114
Total investment securities available-for-sale, Fair Value	$ 2,207,873