Segment Reporting (Schedule Of Net Revenues Earned On Major Geographical Areas) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Total net revenues	[1]	$ 641,986	$ 591,575	$ 1,914,105	$ 1,750,308
United States [Member]
Segment Reporting Information [Line Items]
Total net revenues		602,422	567,153	1,796,143	1,654,500
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total net revenues		37,139	22,174	110,731	88,022
Other European [Member]
Segment Reporting Information [Line Items]
Total net revenues		$ 2,425	$ 2,248	$ 7,231	$ 7,786

[1] No individual client accounted for more than 10 percent of total net revenues for the three and nine months ended September 30, 2016 or 2015.