Segment Reporting (Schedule Of Net Revenues Earned On Major Geographical Areas) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Total net revenues	[1]	$ 1,134,789	$ 913,034
United States [Member]
Segment Reporting Information [Line Items]
Total net revenues		1,015,895	860,132
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total net revenues		61,218	37,738
Canada [Member]
Segment Reporting Information [Line Items]
Total net revenues		42,356	3,543
Other [Member]
Segment Reporting Information [Line Items]
Total net revenues		$ 15,320	$ 11,621

[1] No individual client accounted for more than 10 percent of total net revenues for the three months ended March 31, 2021 or 2020.