Commitments and contingencies - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Commitments and Contingencies Disclosure [Line Items]
Gain Loss On Liquidations Of Subsidiary	$ 149,000	$ 0
Selling, General and Administrative Expenses [Member]
Commitments and Contingencies Disclosure [Line Items]
Settlement of trade debt	374,000
Adjustment of an accrual based upon actual reduced liability	$ 44,000