Accumulated Other Comprehensive Loss (Reclassifications Out of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense)/benefit	$ (5,200)	$ (11,312)	$ (12,434)	$ (12,955)	$ (61,234)	$ (10,253)	$ (23,036)	$ (12,257)	$ (18,969)	$ (2,848)	$ (10,532)	$ (9,757)	$ (41,901)	$ (106,780)	$ (42,106)
Net (income) loss													10,613	(7,002)	(1,395)
Interest on short-term borrowings													37,510	19,052	1,357
Net income	$ 73,039	$ 70,397	$ 68,988	$ 71,596	$ 9,446	$ 40,459	$ 52,014	$ 47,604	$ 47,168	$ 11,484	$ 25,775	$ 23,605	284,020	149,523	108,032
Unrealized gains (losses) on securities carried at fair value, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net (income) loss													177	(4,802)	84
Unrealized gains (losses) on securities carried at fair value, 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													224	(7,388)	129
Income tax (expense)/benefit													(47)	2,586	(45)
Net income													177	(4,802)	84
Amortization of defined benefit pension plan items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries, wages and employee benefits (operating expenses)													11,339	(1,752)	(2,276)
Income tax expense/(benefit)													(2,381)	613	797
Net (income) loss													8,958	(1,139)	(1,479)
Unrealized gains (losses) on cash flow hedges, net of tax
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net (income) loss													1,478	(1,061)	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)													393	(572)	0
Interest on short-term borrowings													(1,871)	1,633	0
Net income													$ (1,478)	$ 1,061	$ 0