Securities purchased under agreements to resell (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Securities Purchased Under Agreements To Resell [Line Items]
Repledged	$ 145,866	$ 189,308
Not repledged	33,258	20,734
Total	$ 179,124	$ 210,042

Fair value of the collateral, or portion thereof, that has been re-pledged, delivered, or otherwise used.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=7523297&loc=SL6224234-111729

Name:	us-gaap_FairValueOfSecuritiesReceivedAsCollateralThatHaveBeenResoldOrRepledged
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant