Organization and basis of presentation - Additional Information (Detail) (Contran Corporation [Member])	Sep. 30, 2012
Contran Corporation [Member]
Noncontrolling Interest [Line Items]
Ownership Percentage	88.00%

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

No definition available.

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant