Segment Reporting - Net Revenues by Geographic Locations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]
Net revenues	$ 159,426	$ 128,314	$ 497,590	$ 337,619
United States
Segment Reporting Information [Line Items]
Net revenues	153,375	126,458	486,251	329,379
Europe
Segment Reporting Information [Line Items]
Net revenues	$ 6,051	$ 1,856	$ 11,339	$ 8,240

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income after deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration