Selected quarterly financial data (unaudited) - Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 9,997	$ 8,910	$ 13,296	$ 12,471	$ 19,243	$ 11,528	$ 7,851	$ 15,957	$ 44,674	$ 54,579	$ 35,427
Total operating expenses	240,531	219,326	215,998	183,645	176,204	161,347	156,465	132,586	859,500	626,602	367,592
Loss from operations	(230,534)	(210,416)	(202,702)	(171,174)	(156,961)	(149,819)	(148,614)	(116,629)	(814,826)	(572,023)	(332,165)
Net loss	$ (223,347)	$ (206,033)	$ (195,782)	$ (164,446)	$ (149,023)	$ (145,480)	$ (145,996)	$ (115,126)	$ (789,608)	$ (555,625)	$ (335,643)
Net loss per share applicable to common stockholders - basic and diluted:	$ (4.04)	$ (3.73)	$ (3.55)	$ (2.99)	$ (2.72)	$ (2.73)	$ (2.91)	$ (2.31)	$ (14.31)	$ (10.68)	$ (7.71)

Total costs of sales and operating expenses for the period.

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