Borrowings (Short-term borrowings) (Details 1) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Short-term Borrowings
Securities Sold Under Agreements to Repurchase	$ 505,293	$ 523,378
Funds Purchased
Short-term Borrowings
Amounts Outstanding	$ 0	$ 9,616
Weighted Average Interest Rate (as a percent)	0.00%	0.15%
Securities Sold Under Agreements to Repurchase
Short-term Borrowings
Amounts Outstanding	$ 1,603	$ 23,278
Weighted Average Interest Rate (as a percent)	0.14%	0.31%
Long-term Repurchase Agreements with Government Entities
Short-term Borrowings
Securities Sold Under Agreements to Repurchase	$ 3,700	$ 100
Long-term Repurchase Agreements with Private Institutions
Short-term Borrowings
Securities Sold Under Agreements to Repurchase	$ 500,000	$ 500,000