Securities (Schedule of Contractual Maturities of Investment Securities Available for Sale) (Details) $ in Thousands	Mar. 31, 2017 USD ($)
Available-for-sale Securities [Abstract]
Due within one year, Amortized Cost	$ 53,518
Due after one year through five years, Amortized Cost	502,633
Due after five years through ten years, Amortized Cost	731,123
Due after ten years, Amortized Cost	1,056,591
No stated maturity date, Amortized Cost Basis	5,284
Total investment securities available-for-sale, Amortized Cost	2,349,149
Due within one year, Fair Value	53,606
Due after one year through five years, Fair Value	505,398
Due after five years through ten years, Fair Value	724,361
Due after ten years, Fair Value	1,042,923
No stated maturity date, Fair Value	5,071
Total investment securities available-for-sale, Fair Value	$ 2,331,359