Regulatory Requirements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Regulatory Capital Requirements [Abstract]
Net assets held by regulated subsidiaries	$ 336.8us-gaap_NetRegulatoryAssets
Aggregate regulatory net capital	$ 156.4us-gaap_ExcessCapital

The amount by which the company's Total Capital exceeds the minimum required for capital adequacy purposes.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

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