Securities (Amortized Cost and Fair Value of Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Securities [Abstract]
Debt Securities Available for Sale, Due in one year or less, Amortized Cost	$ 1,862
Debt Securities Available for Sale, Due after one year through five years, Amortized Cost	105,364
Debt Securities Available for Sale, Due after five years through ten years, Amortized Cost	1,200,188
Debt Securities Available for Sale, Due after ten years, Amortized Cost	1,448,392
Total available for sale debt securities, Amortized Cost	2,755,806
Debt Securities Available for Sale, Due in one year or less, Fair Value	1,868
Debt Securities Available for Sale, Due after one year through five years, Fair Value	106,255
Debt Securities Available for Sale, Due after five years through ten years, Fair Value	1,163,870
Debt Securities Available for Sale, Due after ten years, Fair Value	1,419,044
Total available for sale debt securities, Fair Value	2,691,037
Debt Securities Held to Maturity, Due in one year or less, Amortized Cost	18,654
Debt Securities Held to Maturity, Due after one year through five years, Amortized Cost	127,861
Debt Securities Held to Maturity, Due after five years through ten years, Amortized Cost	1,425,846
Debt Securities Held to Maturity, Due after ten years, Amortized Cost	1,407,186
Total held to maturity debt securities, Amortized Cost	2,979,547	$ 2,977,511
Debt Securities Held to Maturity, Due in one year or less, Fair Value	18,676
Debt Securities Held to Maturity, Due after one year through five years, Fair Value	126,495
Debt Securities Held to Maturity, Due after five years through ten years, Fair Value	1,405,836
Debt Securities Held to Maturity, Due after ten years, Fair Value	1,384,849
Total held to maturity debt securities, Fair Value	$ 2,935,856	$ 2,962,010