Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Selected Quarterly Financial Data [Line Items]
Total revenue	$ 23,462	$ 30,033	$ 48,847	$ 50,573	$ 33,862	$ 29,218	$ 23,315	$ 28,222	$ 152,915	$ 114,617	$ 1,193,323
Cost of goods sold	4,323	5,570	5,773	3,811	5,989	4,927	5,018	5,440	19,477	21,374	24,412
Research and development expenses	102,724	100,531	96,436	108,987	110,369	99,048	106,686	118,463	408,678	434,566	399,536
Operating loss	(110,721)	(103,050)	(77,709)	(133,631)	(109,638)	(98,740)	(110,970)	(120,687)	(425,111)	(440,035)	687,932
Net income (loss)	$ (117,203)	$ (108,586)	$ (80,000)	$ (138,651)	$ (112,164)	$ (98,585)	$ (110,286)	$ (119,632)	$ (444,440)	$ (440,667)	$ 681,313
Net income (loss) per share
Basic ( in dollars per share)	$ (0.65)	$ (0.61)	$ (0.45)	$ (0.78)	$ (0.64)	$ (0.56)	$ (0.63)	$ (0.69)	$ (2.49)	$ (2.52)	$ 4.02
Diluted (in dollars per share)	$ (0.65)	$ (0.61)	$ (0.45)	$ (0.78)	$ (0.64)	$ (0.56)	$ (0.63)	$ (0.69)	$ (2.49)	$ (2.52)	$ 3.78
Product Sales
Selected Quarterly Financial Data [Line Items]
Total revenue	$ 2,884	$ 5,691	$ 5,485	$ 3,444	$ 5,815	$ 5,558	$ 4,346	$ 4,398	$ 17,504	$ 20,117	$ 20,774