Segment Reporting (Schedule Of Net Revenues Earned On Major Geographical Areas) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Total net revenues	$ 578,076	$ 523,455	$ 560,147	$ 546,746	$ 562,526	$ 478,639	$ 493,678	$ 438,604	$ 2,208,424	[1]	$ 1,973,446	[1]	$ 1,594,113	[1]
United States [Member]
Segment Reporting Information [Line Items]
Total net revenues									2,082,876		1,894,300		1,561,665
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total net revenues									113,943		67,394		23,140
Other European [Member]
Segment Reporting Information [Line Items]
Total net revenues									$ 11,605		$ 11,752		$ 9,308

[1] No individual client accounted for more than 10 percent of total net revenues for the years ended December 31, 2014, 2013, or 2012.