Shareholders' Equity - Narrative (Details) $ / shares in Units, $ in Thousands			1 Months Ended		2 Months Ended	12 Months Ended
	Nov. 01, 2016 USD ($) $ / shares shares	Oct. 18, 2016	Aug. 31, 2016 shares	Jun. 30, 2016 shares	Mar. 31, 2016 USD ($) $ / shares shares	Mar. 31, 2017 USD ($) bank $ / shares shares	Feb. 02, 2016 class
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of classes of shares | class							1
Common shares authorized (in shares)					564,111,242	564,111,242
Common shares par value (in USD per share) | $ / shares					$ 0.000017727	$ 0.000017727
Options granted (in shares)						1,525,857
Reverse stock split ratio		0.5641
Shares sold, price (in USD per share) | $ / shares						$ 15.00
Gross proceeds on sale of shares | $						$ 199,964
Net proceeds on sale of shares | $					$ 0	$ 202,275
Number of banking institutions | bank						1
Shares issued to settle the warrant liability to Takeda (in shares)						2,339,192
Initial Public Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares sold (in shares)	14,500,000
Shares sold, price (in USD per share) | $ / shares	$ 15.00
Gross proceeds on sale of shares | $	$ 217,500
Net proceeds on sale of shares | $	200,000
Underwriting discounts and commissions | $	15,200
Offering expenses | $	$ 2,300
Shares issued to settle the warrant liability to Takeda (in shares)						1,977,269
Restricted Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards granted (in shares)				1,128,222		1,128,222
Shares issued to settle the warrant liability to Takeda (in shares)						153,846
Employee and Non-employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)			602,743			1,525,857
Shares issued to settle the warrant liability to Takeda (in shares)						208,077