Regulatory Requirements - Additional Information (Detail) $ in Millions	Jun. 30, 2015 USD ($)
Regulatory Capital Requirements [Abstract]
Net assets held by regulated subsidiaries	$ 514.1
Amount of capital in excess of aggregate regulatory requirements	$ 243.7

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