Common stock - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended		123 Months Ended	0 Months Ended
	Mar. 06, 2014 Directors	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 06, 2014 Non-employee Directors [Member]	Jan. 27, 2014 Equity Incentive Plan 2006 [Member]	Jan. 27, 2014 Equity Incentive Plan 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted		0			33,332	0
Maximum number of shares of common stock that may be issued							1,423,416
Common stock, shares outstanding							756,279
Shares of common stock reserved for issuance description		Additionally, the number of shares of common stock reserved for issuance under the 2014 Plan will automatically increase on January 1 of each year for a period of up to 10 years, beginning on January 1, 2015 and ending on and including January 1, 2024, by 4% of the total number of shares of capital outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the board of directors.
Shares of common stock reserved for issuance percentage		4.00%
Years of increase in shares of common stock reserved for issuance		10 years
Exercise price per share of options granted to non-employee directors					$ 11.00
Number of non-employee directors	4
Weighted average grant date fair value of stock options granted		$ 9.05	$ 0.00	$ 4.23
Stock-based compensation expense		$ 137,654	$ 54,674	$ 1,409,722
Unrecognized stock-based compensation cost		$ 1,485,971		$ 1,485,971
Unrecognized stock-based compensation cost, weighted-average period recognized		1 year 5 months 19 days