Accrued liabilities - Additional Information (Detail) (AA And Saba Consultants [Member], USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2014
AA And Saba Consultants [Member]
Accrued Liabilities And Other Liabilities [Line Items]
Settlement amount paid	$ 4.5
Reduction in accrued judgements and settlements	$ 1

The amount of cash paid for the settlement of litigation or for other legal issues during the period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

Name:	us-gaap_PaymentsForLegalSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration