Accumulated Other Comprehensive Income (Schedule Of Accumulated Other Comprehensive Income Reclassifications) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues	$ 1,458,977	$ 1,102,593	$ 3,863,914	$ 3,735,702
Reclassification for the period, net of tax			14,193	(5,352)
Net unrealized losses on available for sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification for the period, tax			37	14
Net unrealized foreign exchange losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification for the period, tax			(16)	1,086
Net unrealized losses on instrument specific credit risk
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification for the period, tax			126	0
Amortization of defined benefit pension plan actuarial gains (losses)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification for the period, net of tax			(1,398)	(1,297)
Reclassification for the period, tax			(508)	(604)
Other pension
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification for the period, net of tax			(5,344)	1,231
Reclassification for the period, tax			0	(1,231)
Reclassification out of Accumulated Other Comprehensive Income | Net unrealized foreign exchange losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income and other expenses			20,459	(5,310)
Other
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues	296,548	67,811	440,537	366,335
Other | Reclassification out of Accumulated Other Comprehensive Income | Net unrealized losses on available for sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues			105	24
Principal transactions
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues	$ 116,204	$ 84,143	315,622	725,780
Principal transactions | Reclassification out of Accumulated Other Comprehensive Income | Net unrealized losses on instrument specific credit risk
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues			$ 371	$ 0