Accumulated Other Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net			$ 2,132	$ (11)
Total before tax	$ 63,818	$ 51,748	120,474	98,533
Income tax provision	(12,094)	(9,999)	(22,879)	(16,814)
Compensation and employee benefits	52,015	48,949	104,100	99,519
Net income	51,724	41,749	97,595	81,719
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains and Losses on Available-for-Sale Debt Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net	285	5	2,132	107
Total before tax	285	5	2,132	107
Income tax provision	(66)	(1)	(496)	(25)
Net income	219	4	1,636	82
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains and Losses on Pension Plan Liability [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(80)	(80)	(159)	(160)
Income tax provision	19	19	37	38
Compensation and employee benefits	(80)	(80)	(159)	(160)
Net income	$ (61)	$ (61)	$ (122)	$ (122)