Segment Reporting (Schedule Of Net Revenues Earned On Major Geographical Areas) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Total net revenues	[1]	$ 652,145	$ 597,751	$ 1,272,119	$ 1,158,733
United States [Member]
Segment Reporting Information [Line Items]
Total net revenues		611,984	564,731	1,193,721	1,087,347
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total net revenues		37,844	30,562	73,592	65,848
Other European [Member]
Segment Reporting Information [Line Items]
Total net revenues		$ 2,317	$ 2,458	$ 4,806	$ 5,538

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