Short-Term Borrowings (Short-Term Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Amount outstanding at period-end	$ 1,225,406	$ 1,423,644
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Amount outstanding at period-end	2,275	10,100
Average amount outstanding during period	14,052	15,992
Maximum amount at any month-end during period	$ 59,475	$ 13,675
Weighted-average interest at period-end	0.38%	0.13%
Weighted-average interest rate during period	0.50%	0.26%
Securities Sold Under Agreements to Repurchase [Member]
Short-term Debt [Line Items]
Amount outstanding at period-end	$ 358,131	$ 513,544
Average amount outstanding during period	454,571	539,169
Maximum amount at any month-end during period	$ 579,099	$ 609,671
Weighted-average interest at period-end	0.04%	0.03%
Weighted-average interest rate during period	0.03%	0.03%
FHLB Borrowings [Member]
Short-term Debt [Line Items]
Amount outstanding at period-end	$ 865,000	$ 900,000
Average amount outstanding during period	943,570	469,973
Maximum amount at any month-end during period	$ 1,175,000	$ 900,000
Weighted-average interest at period-end	0.54%	0.32%
Weighted-average interest rate during period	0.41%	0.18%