Net Capital Requirements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Brokers And Dealers [Abstract]
Aggregate net capital and financial resources in excess of required level	$ 81.1us-gaap_AlternativeExcessNetCapital
Aggregate net capital and financial resources, minimum capital requirement	$ 12.4

Amount of net capital requirement computed under the alternative method allowed under regulatory reporting requirements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Rule 15c3

-Number 240

-Section 1

-Paragraph 1

-Subparagraph ii

-Article 15c3

-Subsection a

Name:	us-gaap_AlternativeNetCapitalRequirement1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant