Receivable from and Payable to Customers (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Receivables and Payable to Customers [Abstract]
Receivables from customers, net of allowance of $570 and $1,550, respectively	$ 45,966	$ 49,891
Payables to customers	$ 412,646	$ 352,467

Amounts payable to customers at the balance sheet date. The term customers generally excludes other broker-dealers; persons who are principal officers, directors, and stockholders; and persons whose securities or funds are part of the regulatory net capital of the broker-dealer. Another broker-dealer's account can be classified as a customer if the account is carried as an omnibus account in compliance with certain regulations. The accounts of principal officers, directors and stockholders may be combined in the customer captions if they are not material and the combination is disclosed in the oath that is required to accompany the annual audited FOCUS Report.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Name:	us-gaap_PayablesToCustomers
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant