Long-term debt - CompX - Additional Information (Detail) (CompX [Member], Promissory Note [Member])	Mar. 31, 2013
CompX [Member] \| Promissory Note [Member]
Line of Credit Facility [Line Items]
Average interest rate on long-term debt	1.30%

Reflects the calculation as of the balance sheet date of the average interest rate weighted by the amount of long-term debt outstanding by type or by instrument at that time.

No definition available.

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