Stock-based compensation (Details 2) (USD $)	1 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended				0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended	0 Months Ended
	Nov. 30, 2011 Former employee 2011 Plan	Dec. 31, 2011 Stock options	Dec. 31, 2012 Stock options	Dec. 31, 2011 Stock options Minimum	Dec. 31, 2012 Stock options Minimum	Dec. 31, 2011 Stock options Maximum	Dec. 31, 2012 Stock options Maximum	Dec. 31, 2011 Stock options Employees	Dec. 31, 2012 Stock options Employees	Dec. 31, 2011 Stock options Non-employees	Dec. 31, 2012 Stock options Non-employees	Dec. 31, 2012 Restricted stock	Dec. 31, 2012 Restricted stock Employees	Dec. 31, 2012 Restricted stock units	Dec. 05, 2012 Restricted stock units CEO	Dec. 31, 2012 Restricted stock units CEO	Dec. 31, 2012 Time based restricted stock units	Dec. 05, 2012 Time based restricted stock units CEO	Dec. 31, 2012 Time based restricted stock units CEO	Dec. 05, 2012 Performance based restricted stock units CEO
Shares
Outstanding at the beginning of the period (in shares)			617,633
Granted (in shares)		452,294	718,936						679,251	165,339	39,685
Exercised (in shares)			(5,792)
Forfeited (in shares)			(112,624)
Outstanding at the end of the period (in shares)		617,633	1,218,153
Exercisable at the end of the period (in shares)			175,814
Vested and expected to vest at the end of the period (in shares)			1,114,651
Weighted average exercise price per share
Outstanding at the beginning of the period (in dollars per share)			$ 0.04
Granted (in dollars per share)			$ 6.49						$ 6.59	$ 0.04	$ 4.81
Exercised (in dollars per share)			$ 0.04
Forfeited (in dollars per share)			$ 0.26
Outstanding at the end of period (in dollars per share)		$ 0.04	$ 3.83
Exercisable at the end of the period (in dollars per share)			$ 0.44
Vested and expected to vest at the end of the period (in dollars per share)			$ 3.78
Weighted average remaining contractual term
Outstanding at the end of the period		9 years 9 months 18 days	9 years 4 months 2 days
Exercisable at the end of the period			8 years 10 months 2 days
Vested and expected to vest at the end of the period			8 years 10 months 2 days
Outstanding at the end of the period		9 years 9 months 18 days	9 years 4 months 2 days
Aggregate intrinsic value
Outstanding at the end of period			$ 2,162,000
Exercisable at the end of period			1,394,000
Vested and expected to vest at the end of the period			5,123,000
Outstanding at the end of period		2,162,000	5,535,000
Shares
Unvested at the beginning of the period (in shares)												2,319,646
Granted (in shares)														192,308	192,308			128,205		64,103
Vested (in shares)												674,505
Unvested at the end of the period (in shares)												1,645,141		192,308
Weighted-Average Grant Date Fair Value
Granted (in dollars per share)													$ 7.80	$ 7.80				$ 7.80
Unvested at the end of the period (in dollars per share)														$ 7.80
Vested (in dollars per share)												$ 0.002
Weighted-average purchase price per share
Outstanding at the beginning of the period (in dollars per share)												$ 0.002
Vested (in dollars per share)												$ 0.002
Outstanding at the end of the period (in dollars per share)												$ 0.002
Weighted Average Remaining Contractual Term
Non-vested at the beginning of the period														2 years
Granted														2 years
Non-vested at the end of the period														2 years
Aggregate Intrinsic Value
Granted														$ 1,500,000
Non-vested at the end of the period														$ 1,500,000
Assumptions used to estimate fair value of each stock-based award on the grant date using the Black-Scholes option pricing model
Risk free interest rate (as a percent)				1.20%	0.80%	1.84%	1.78%
Volatility (as a percent)				79.00%	79.00%	79.00%	89.00%
Expected term				6 years	5 years 1 month 6 days	9 years 9 months	9 years 11 months 5 days
Additional disclosures
Weighted average grant-date fair value of options granted (in dollars per share)									$ 4.82
weighted average exercise price (in dollars per share)																$ 0.001
Issue price (in dollars per share)	$ 0.002
Shares issued	19,772
Stock-based compensation expense								26,000	346,000	320,000	999,000								36,000
Total unrecognized compensation cost related to non-vested stock options and restricted stock (in dollars)			$ 7,118,000														$ 964,000
Weighted average period for recognition of compensation cost related to unvested stock awards			2 years 10 months 24 days														2 years		2 years
Future quarterly restricted stock unit award grant																		16,025