Significant accounting policies - Amortization of Intangible Assets Estimated Economic Lives (Detail)	9 Months Ended
Sep. 30, 2013
Trademark [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life	4 years 8 months 12 days
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable Life	7 years

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration