Stockholders' equity - Additional Information (Detail) (USD $)	1 Months Ended		9 Months Ended			9 Months Ended			3 Months Ended	9 Months Ended	12 Months Ended
	Aug. 26, 2011	Apr. 29, 2011	Sep. 30, 2012	Dec. 31, 2011	Sep. 01, 2011	Sep. 30, 2012 Stock Purchase Agreement [Member]	Sep. 30, 2012 Roth Warrant [Member]	Sep. 01, 2011 Roth Warrant [Member]	Sep. 30, 2012 Private Placement [Member]	Sep. 30, 2012 Private Placement [Member]	Dec. 31, 2011 Private Placement [Member]	Apr. 29, 2011 Private Placement [Member]
Sale Of Stock [Line Items]
Common stock, shares authorized			50,000,000	50,000,000
Common stock, par value			$ 0.001	$ 0.001
Common stock, shares issued			9,909,212	9,895,462
Common stock, shares outstanding		10,000,000	9,078,287
Private Placement proceeds allocated to preferred stock and Private Placement Warrants		$ 18,000,000
Common equity value as adjusted for the Reverse Split		$ 10.08
Number of converted shares of preferred stock issued in Private Placement		1,500,009
Price per warrant		$ 3.85
Shares of common stock issuable upon exercise of the Private Placement Warrant			736,252							750,002
Preferred equity value		9,700,000
Value assigned to the Company preferred stock												15,100,000
Amount of preferred stock converted into common stock			1,000
Preferred stock conversion price per share	$ 12.00		$ 12.00
Warrants expiry date							Apr. 29, 2016		Apr. 29, 2016	Apr. 29, 2016
Aggregate sale of shares		18,000	18,000
Estimated fair value		2,887,000
Volatility factor		50.00%	55.00%								60.00%
Risk-free interest rate		2.10%
Private Placement Warrants term										5 years
Exercise price per share							$ 13.20		$ 13.00	$ 13.00
Dividend yield			0.00%
Private placement warrants exercised									13,750
Adjusted shares of common stock		3,360,000			105,000		62,116	62,116
Estimated fair value of the Roth Warrant		400,000
Share price for warrant issuable		$ 3.80
Warrant shares issuable			42,884
Common stock repurchased by the company, shares			830,925	830,925		830,925
Common stock repurchased by the company, value			4,250,000	4,250,000		4,250,000
Common stock repurchased by the company, per share value						$ 5.11
Repurchase of common stock						830,925
Transaction costs incurred in connection with the Reverse Recapitalization and the Private Placement consist of cash costs			5,700,000
Allocated equity			4,900,000
Costs allocated to the Private Placement Warrants			800,000
Costs for filing registration statements				600,000
Gross proceeds from issuance of common stock and additional warrant			5,000,000
Eligible period to use a registration statement			30 days
Filing registration, condition for suspension, description			(which period may not be for more than 20 consecutive days or for a total of more than 45 days in any 12-month period)
Payment to investors			1.50%
Liquidated damages			$ 300,000