Consolidated Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Collaboration and license revenue	$ 0	$ 33,558,000	$ 11,442,000
Operating expenses:
Repurchase of royalty rights	80,000,000
Research and development	146,171,000	68,774,000	48,136,000
Selling, general and administrative	61,663,000	38,435,000	21,973,000
Total operating expenses	287,834,000	107,209,000	70,109,000
Loss from operations	(287,834,000)	(73,651,000)	(58,667,000)
Interest and other income, net	11,621,000	5,953,000	1,657,000
Net loss	(276,213,000)	(67,698,000)	(57,010,000)
Other comprehensive income (loss)	616,000	125,000	(200,000)
Comprehensive loss	$ (275,597,000)	$ (67,573,000)	$ (57,210,000)
Net loss per share, basic and diluted	$ (6.17)	$ (1.76)	$ (1.74)
Weighted average number of shares used to compute net loss per share, basic and diluted	44,765,496	38,386,906	32,832,514