Securities (Schedule of Contractual Maturities of Investment Securities Available for Sale) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Available-for-sale Securities [Abstract]
Due within one year, Amortized Cost	$ 15,480
Due after one year through five years, Amortized Cost	404,752
Due after five years through ten years, Amortized Cost	526,230
Due after ten years, Amortized Cost	1,030,231
No stated maturity date, Amortized Cost Basis	5,284
Total investment securities available-for-sale, Amortized Cost	1,981,977
Due within one year, Fair Value	15,601
Due after one year through five years, Fair Value	406,989
Due after five years through ten years, Fair Value	534,584
Due after ten years, Fair Value	1,044,773
No stated maturity date, Fair Value	5,212
Total investment securities available-for-sale, Fair Value	$ 2,007,159