Financial instruments - Fair Value of Significant Unobservable Inputs (Detail) (Level 3 [Member], USD $)	3 Months Ended
	Mar. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 1,021,526
Change in fair value of derivative liabilities	(113,723)
Derecognition of liabilities upon preferred stock conversion to common stock conversion	(800,206)
Ending balance	107,597
Warrant Derivative Liabilities [Member] | Bank Loan [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	221,320
Change in fair value of derivative liabilities	(113,723)
Derecognition of liabilities upon preferred stock conversion to common stock conversion
Ending balance	107,597
Embedded Derivative Liabilities [Member] | Preferred Stock [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	800,206
Change in fair value of derivative liabilities
Derecognition of liabilities upon preferred stock conversion to common stock conversion	(800,206)
Ending balance