Common stock (Details) (USD $)	1 Months Ended		3 Months Ended	24 Months Ended			0 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended			1 Months Ended
	Aug. 31, 2012	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2013	Dec. 31, 2012	Aug. 13, 2012 item	Mar. 18, 2013 Common stock	Mar. 31, 2013 Common stock	Sep. 13, 2012 Issuance under private placement	Mar. 31, 2013 Issuance under private placement	Aug. 31, 2012 Issuance under private placement	Aug. 13, 2012 Issuance under private placement	Aug. 31, 2012 Series A Preferred Stock Issuance under private placement	Aug. 31, 2012 Series B Preferred Stock Issuance under private placement
Common stock
Reverse stock split conversion ratio		2.023
Common stock
Number of common stock issued (in shares)											897,554
Common stock issue price (in dollars per share)								$ 9.00				$ 5.50
Aggregate purchase price											$ 4,039,000
Preferred stock conversion ratio													2.023
Number of shares of common stock in which preferred stock is convertible													3,064,753	6,770,563
Number of common shares to be included in the Resale S-1									7,630,683		897,554			6,770,563
Number of classes of board of directors						3
Staggered term of board of directors	3 years
Percentage of the shares of capital stock, whose holders' affirmative vote is required to remove directors	75.00%
Outstanding stock options and outstanding restricted stock units (in shares)			2,663,595	2,663,595	1,410,461
Common stock issued in a private placement (in shares)								3,888,880
Net proceeds from issuance of common stock			32,652,000	36,693,000						32,652,000
Aggregate purchase price for common stock issued in a private placement							$ 34,999,920