Selected quarterly financial data (unaudited) - Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 1,606	$ 1,019	$ 143	$ 894	$ 0	$ 0	$ 0	$ 0	$ 3,662	$ 0	$ 0
Total operating expenses	137,273	155,468	154,844	146,988	139,387	131,743	143,650	144,479	594,573	559,259	562,963
Loss from operations	(135,667)	(154,449)	(154,701)	(146,094)	(139,387)	(131,743)	(143,650)	(144,479)	(590,911)	(559,259)	(562,963)
Net loss from continuing operations	(132,327)	(152,834)	(155,973)	(121,504)	(136,321)	(137,678)	(140,665)	(146,392)	(562,638)	(561,056)	(555,022)
Net income (loss) from discontinued operations	(22,725)	(63,982)	(85,729)	(84,304)	(63,553)	(57,067)	119,200	(56,219)	(256,740)	(57,639)	(234,586)
Net loss	$ (155,052)	$ (216,816)	$ (241,702)	$ (205,808)	$ (199,874)	$ (194,745)	$ (21,465)	$ (202,611)	$ (819,378)	$ (618,695)	$ (789,608)
Net loss per share from continuing operations - basic (in dollars per share)	$ (1.83)	$ (2.23)	$ (2.31)	$ (1.81)	$ (2.05)	$ (2.08)	$ (2.33)	$ (2.63)	$ (8.16)	$ (9.02)	$ (10.06)
Net loss per share from continuing operations - diluted (in dollars per share)	(1.83)	(2.23)	(2.31)	(1.81)	(2.05)	(2.08)	(2.33)	(2.63)	(8.16)	(9.02)	(10.06)
Net income (loss) per share from discontinued operations - basic	(0.31)	(0.93)	(1.27)	(1.26)	(0.96)	(0.86)	1.97	(1.01)	(3.73)	(0.93)
Net income (loss) per share from discontinued operations - diluted	(0.31)	(0.93)	(1.27)	(1.26)	(0.96)	(0.86)	1.97	(1.01)	(3.73)	(0.93)
Net loss per share - basic (in dollars per share)	(2.14)	(3.16)	(3.58)	(3.07)	(3.01)	(2.94)	(0.36)	(3.64)	(11.89)	(9.95)	(14.31)
Net loss per share - diluted (in dollars per share)	$ (2.14)	$ (3.16)	$ (3.58)	$ (3.07)	$ (3.01)	$ (2.94)	$ (0.36)	$ (3.64)	$ (11.89)	$ (9.95)	$ (14.31)