Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development (includes $1,041 and $1,060 of share-based compensation expense for the three months ended December 31, 2017 and 2016 and $2,580 and $2,849 for the nine months ended December 31, 2017 and 2016, respectively)	$ 34,875	$ 6,158	$ 76,753	$ 24,484
General and administrative (includes $2,252 and $950 of share-based compensation expense for the three months ended December 31, 2017 and 2016 and $5,663 and $3,932 for the nine months ended December 31, 2017 and 2016, respectively)	6,640	2,898	16,963	8,427
Total operating expenses	41,515	9,056	93,716	32,911
Other expenses:
Changes in the fair value of the Takeda warrant liability	0	(1,002)	0	28,815
Interest expense	904	0	904	0
Other income	(429)	0	(225)	0
Loss before provision for income taxes	(41,990)	(8,054)	(94,395)	(61,726)
Income tax (benefit) expense	(213)	29	607	40
Net loss	$ (41,777)	$ (8,083)	$ (95,002)	$ (61,766)
Net loss per common share — basic and diluted (in USD per share)	$ (0.70)	$ (0.15)	$ (1.60)	$ (1.34)
Weighted average common shares outstanding — basic and diluted (in shares)	59,629,486	54,447,203	59,446,140	45,929,021