Segment Reporting (Schedule of Net Revenues Earned on Major Geographical Areas) (Details) (USD $) In Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Net revenues	$ 358,857	[1]	$ 328,009	[1]	$ 725,470	[1]	$ 640,039	[1]
Net revenues	358,857		328,009		725,470		640,039
United States [Member]
Net revenues	343,800		320,933		694,809		626,588
Canada [Member]
Net revenues	6,813		0		13,261		0
United Kingdom [Member]
Net revenues	6,088		4,826		12,137		8,717
Other European [Member]
Net revenues	$ 2,156		$ 2,250		$ 5,263		$ 4,734

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