Segment Reporting (Schedule Of Net Revenues Earned On Major Geographical Areas) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Total net revenues	[1]	$ 725,647	$ 652,145	$ 1,401,178	$ 1,272,119
United States [Member]
Segment Reporting Information [Line Items]
Total net revenues		690,930	611,984	1,339,261	1,193,721
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total net revenues		32,771	37,844	57,290	73,592
Other European [Member]
Segment Reporting Information [Line Items]
Total net revenues		$ 1,946	$ 2,317	$ 4,627	$ 4,806

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