Revenues (Revenue from the Rendering of Services) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues [Abstract]
Commissions	$ 96,110	$ 83,648	$ 314,084	$ 301,379
Fees	32,766	25,670	105,542	79,034
Total revenues	$ 128,876	$ 109,318	$ 419,626	$ 380,413

Aggregate revenue during the period for services rendered in the normal course of business (before deducting allowances and discounts) which are not otherwise defined in the taxonomy.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(d))
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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