Stock option activities (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options Outstanding, at begining of period	3,040,000
Number of options Exercisable	1,676,250
Number of options Outstanding, at end of period	3,040,000	3,040,000
Number of options Exercisable	883,125	1,676,250
Weighted Average Exercise Price Outstanding, at beginning of period	$ 1.95
Weighted Average Exercise Price Exercisable	$ 2.09
Weighted Average Exercise Price Outstanding, at end of period	$ 1.95	$ 1.95
Weighted Average Exercise Price Exercisable	$ 2.43	$ 2.09
Weighted Average Remaining Life in Years Outstanding	7 years 10 months 10 days	8 years 7 months 10 days
Weighted Average Remaining Life in Years Exercisable	7 years 9 months 14 days	8 years 4 months 6 days
Fair Value Outstanding, at begining of period	3,635,372
Fair Value Exercisable	2,024,969
Fair Value Outstanding, at end of period	3,635,372
Fair Value Exercisable	1,082,249	2,024,969