CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses:
Research and development	$ 22,324	$ 30,848	$ 43,225	$ 90,101
General and administrative	9,536	8,441	18,022	16,835
Total operating expenses	31,860	39,289	61,247	106,936
Loss from operations	(31,860)	(39,289)	(61,247)	(106,936)
Interest income	266	1,724	1,055	3,533
Loss before (provision) benefit for income taxes	(31,594)	(37,565)	(60,192)	(103,403)
(Provision) benefit for income taxes	(5,875)	374	(3,696)	391
Net loss	$ (37,469)	$ (37,191)	$ (63,888)	$ (103,012)
Net loss per share attributable to common shareholders-basic and diluted	$ (0.65)	$ (0.68)	$ (1.13)	$ (1.94)
Weighted average common shares outstanding-basic and diluted	57,914,105	54,475,476	56,618,397	53,225,710
Comprehensive loss:
Net loss	$ (37,469)	$ (37,191)	$ (63,888)	$ (103,012)
Other comprehensive income:
Unrealized gain (loss) on short-term investments and currency translation adjustments, net of tax	(231)	93	(24)	105
Total other comprehensive income	(231)	93	(24)	105
Total comprehensive loss	$ (37,700)	$ (37,098)	$ (63,912)	$ (102,907)