License Agreements - AstoZeneca Agreement (Details) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended
	May 31, 2017 shares	Oct. 31, 2016 USD ($) $ / shares shares	Feb. 29, 2016 $ / shares shares	Mar. 31, 2017 USD ($)	Jul. 31, 2016 $ / shares shares	Mar. 31, 2016 USD ($)
License agreements
Expiration period based on country by country basis after first commercial sale (in years)		10 years
Fair value of common share | $ / shares			$ 7.00		$ 7.70
Issuance of common shares | shares			429,000		1,090,500
Research and development				$ 10,740		$ 2,370
AstraZeneca | Product related collaborative arrangements
License agreements
Common stock value agreed to issue		$ 10,000
Common shares value issued		$ 5,000
Percentage of shares to be issued upon closing of the transaction		50
Percentage of remaining shares to be issued after contractual events		50
Fair value of common share | $ / shares		$ 9.2911
Preferred stock issued and sold | shares		538,150
Aggregate fair value		$ 5
Other expense for change in the fair value of the derivative liability				1,500
Reclassification of contingent equity to the carrying value		5
Fair value of derivative liability				6,375
Issuance of common shares | shares	538,149
Research and development				$ 0
AstraZeneca | Product related collaborative arrangements | Maximum
License agreements
Milestone payment to be paid		30,000
Milestone payment to be paid for any product other than Rett syndrome		60,000
Commercial milestone payment to be paid		$ 120,000
Right to purchase shares fully diluted (as a percent)		8
AstraZeneca | Product related collaborative arrangements | Minimum
License agreements
Minimum investment in equity		$ 30,000