Significant Accounting Policies - Summary of Result of Adopting ASC 606 on Financial Statement - Condensed Consolidated Statements of Operations and Comprehensive Loss (Detail) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Income Statements Captions [Line Items]
Revenue	$ 4,493,000	$ 1,315,000	$ 10,794,000	$ 2,795,000
Loss from operations	(38,232,000)	(26,353,000)	(110,580,000)	(71,233,000)
Income tax benefit (provision)	0	418,000	(172,000)	(1,035,000)
Net loss	$ (37,631,000)	$ (25,494,000)	$ (108,766,000)	$ (71,187,000)
Net loss per share attributable to ordinary shareholders—basic and diluted	$ (1.28)	$ (0.92)	$ (3.78)	$ (2.73)
As Originally Reported Under ASC 605 [Member] \| ASC 606 [Member]
Condensed Income Statements Captions [Line Items]
Revenue		$ 676,000		$ 2,028,000
Loss from operations		(26,992,000)		(72,000,000)
Income tax benefit (provision)		416,000		(905,000)
Net loss		$ (26,135,000)		$ (71,824,000)
Net loss per share attributable to ordinary shareholders—basic and diluted		$ (0.94)		$ (2.75)
Effect of Change [Member] \| ASC 606 [Member]
Condensed Income Statements Captions [Line Items]
Revenue		$ 639,000		$ 767,000
Loss from operations		639,000		767,000
Income tax benefit (provision)		2,000		(130,000)
Net loss		$ 641,000		$ 637,000
Net loss per share attributable to ordinary shareholders—basic and diluted		$ 0.02		$ 0.02