Summary of significant accounting policies - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Significant Accounting Policies [Line Items]
Entity Incorporation Date Of Incorporation	Jan. 11, 1991
Concentration risk, customer	two customers each accounted for 10% or more of the Company’s revenues	three customers each accounted for 10% or more of the Company’s revenues
Aggregate percentage of revenue the from customers accounted for more than 10%	42.00%	44.00%
Deferred tax asset	$ 5,263,000	$ 6,428,000
Operating loss carryforwards, limitations on use	Approximately $8,000,000 of the Company’s $16,000,000 of NOLs are subject to annual limitations of $1,300,000
Options and warrants excluded from the calculation of diluted shares	75,000	50,000
Production and importation permission description	22 million pounds in 2015 and reduces by approximately 4.5 million pounds each year and end at zero in 2020
Customer
Significant Accounting Policies [Line Items]
Accounts receivable, net	$ 2,325,000	$ 6,337,000