Description of Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended
	Oct. 24, 2017	Sep. 30, 2017	Mar. 31, 2017
Significant Accounting Policies [Line Items]
Accumulated deficit		$ (235,230)	$ (193,301)
Cash holdings and short-term investments		19,500
Expected proceeds receivable from exercise of warrants		$ 48,800
Warrant exercisable date		Jul. 31, 2018
Subsequent Event [Member]
Significant Accounting Policies [Line Items]
Gross proceeds of the private placement	$ 40,200
Private Placement [Member] | Subsequent Event [Member]
Significant Accounting Policies [Line Items]
Issue of shares, shares	7,874,683
Subscription price per share	$ 4.64
Warrants price per warrant	$ 0.125
Issued warrants to acquire ordinary shares	8,414,683
Exercise price of warrants	$ 5.80
Private Placement [Member] | Pre-Funded Warrants [Member] | Subsequent Event [Member]
Significant Accounting Policies [Line Items]
Warrants price per warrant	$ 4.755
Issued warrants to acquire ordinary shares	550,000
Exercise price of warrants	$ 0.01