Short-Term Borrowings (Short-Term Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Amount outstanding at period end	$ 2,714,872	$ 1,589,128
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Amount outstanding at period end	195,450	425
Average amount outstanding during period	49,297	39,968
Maximum amount at any month end during period	$ 202,933	$ 100,925
Weighted-average interest at period end	1.60%	2.00%
Weighted-average interest rate during period	2.30%	2.11%
Securities Sold Under Agreements to Repurchase [Member]
Short-term Debt [Line Items]
Amount outstanding at period end	$ 484,422	$ 428,599
Average amount outstanding during period	493,344	456,000
Maximum amount at any month end during period	$ 518,042	$ 500,345
Weighted-average interest at period end	0.54%	0.32%
Weighted-average interest rate during period	0.52%	0.23%
FHLB Borrowings [Member]
Short-term Debt [Line Items]
Amount outstanding at period end	$ 2,035,000	$ 1,160,104
Average amount outstanding during period	1,399,503	1,694,804
Maximum amount at any month end during period	$ 1,941,774	$ 2,410,258
Weighted-average interest at period end	1.17%	2.48%
Weighted-average interest rate during period	1.96%	2.02%