Borrowings (Short-Term Borrowings) (Details) - Federal Funds Purchased And Repurchase Agreements [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Year End Weighted Rate	0.40%	0.20%	0.10%
Average Weighted Rate	0.30%	0.10%	0.10%
Average Balance Outstanding	$ 1,266,093	$ 1,654,860	$ 1,119,578
Maximum Outstanding at any Month End	1,723,905	2,193,197	1,862,518
Balance at December 31	$ 1,723,905	$ 1,963,552	$ 1,862,518