Accumulated Other Comprehensive Loss (Reclassifications Out of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense)/benefit	$ (61,234)	$ (10,253)	$ (23,036)	$ (12,257)	$ (18,969)	$ (2,848)	$ (10,532)	$ (9,757)	$ (10,200)	$ (9,600)	$ (9,100)	$ (8,100)	$ (106,780)	$ (42,106)	$ (37,000)
Net (loss) gain on sale of investment securities													(7,388)	129	630
Net Income													(7,002)	(1,395)	(2,247)
Interest on short-term borrowings													20,321	1,660	453
Net Income	$ 9,446	$ 40,459	$ 52,014	$ 47,604	$ 47,168	$ 11,484	$ 25,775	$ 23,605	$ 25,504	$ 24,467	$ 19,024	$ 17,835	149,523	108,032	86,830
Unrealized gains (losses) on securities available-for-sale, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income													(4,802)	84	409
Unrealized gains (losses) on securities available-for-sale, net of tax | Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains and losses on available-for-sale securities													(7,388)	129	630
Income tax (expense)/benefit													2,586	(45)	(221)
Net Income													(4,802)	84	409
Amortization of defined benefit pension plan items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries, wages and employee benefits (operating expenses)													(1,752)	(2,276)	(4,086)
Income tax (expense)/benefit													613	797	1,430
Net Income													(1,139)	(1,479)	(2,656)
Unrealized gains (losses) on cash flow hedges, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income													(1,061)	0	0
Unrealized gains (losses) on cash flow hedges, net of tax | Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense)/benefit													(572)	0	0
Interest on short-term borrowings													1,633	0	0
Net Income													$ 1,061	$ 0	$ 0