Rental expense and commitments (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Operating Leased Assets [Line Items]
Operating Leases Future Minimum Payments Due Future Minimum Sublease Rental	$ 3.7

Contractually required future rental payments receivable on noncancelable subleasing arrangements.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717

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