Segment Reporting (Schedule of Net Revenues Earned on Major Geographical Areas) (Details) (USD $) In Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Net revenues	$ 334,214	[1]	$ 340,388	[1]	$ 1,059,684	[1]	$ 980,427	[1]
Net revenues	334,214		340,388		1,059,684		980,427
United States [Member]
Net revenues	324,519		329,350		1,019,328		955,938
Canada [Member]
Net revenues	3,261		4,870		16,522		4,870
United Kingdom [Member]
Net revenues	4,318		4,073		16,455		12,790
Other European [Member]
Net revenues	$ 2,116		$ 2,095		$ 7,379		$ 6,829

[1] No individual client accounted for more than 10 percent of total net revenues for the three and nine months ended September 30, 2011 or 2010.