Segment Reporting (Schedule Of Net Revenues Earned On Major Geographical Areas) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Total net revenues	[1]	$ 721,169	$ 641,986	$ 2,122,347	$ 1,914,105
United States [Member]
Segment Reporting Information [Line Items]
Total net revenues		681,337	602,422	2,020,598	1,796,143
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total net revenues		38,103	37,139	95,393	110,731
Other European [Member]
Segment Reporting Information [Line Items]
Total net revenues		$ 1,729	$ 2,425	$ 6,356	$ 7,231

[1] No individual client accounted for more than 10 percent of total net revenues for the three and nine months ended September 30, 2017 or 2016.