Securities (Schedule of Contractual Maturities of Investment Securities Available for Sale) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available-for-sale Securities [Abstract]
Due within one year, Amortized Cost	$ 161,538
Due after one year through five years, Amortized Cost	635,254
Due after five years through ten years, Amortized Cost	756,950
Due after ten years, Amortized Cost	1,129,912
Securities available-for-sale, amortized cost	2,683,654	$ 2,763,321
Due within one year, Fair Value	161,314
Due after one year through five years, Fair Value	626,693
Due after five years through ten years, Fair Value	737,927
Due after ten years, Fair Value	1,098,111
Total investment securities available-for-sale, Fair Value	$ 2,624,045	$ 2,737,751