Equity - Common Stock - Additional Information (Detail) $ / shares in Units, $ in Thousands, £ in Millions	Dec. 13, 2019 GBP (£) shares	Jul. 29, 2019 USD ($)	Jul. 18, 2019 $ / shares shares	Nov. 29, 2018 USD ($) $ / shares shares	Mar. 05, 2018 shares	Feb. 01, 2018 USD ($) $ / shares shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 13, 2019 $ / shares
Stockholders Equity Note [Line Items]
Accrued expenses and other current liabilities | $							$ 198,641	$ 139,826
American Depositary Shares
Stockholders Equity Note [Line Items]
Issuance of stock (shares) | shares			22,222,223			19,178,082
Sale of stock price per share | $ / shares			$ 18.00
Commissions, price per share | $ / shares			$ 17.235			$ 3.41
Over allotment option, exercisable period			30 days			30 days
American Depositary Shares | Over-Allotment Option
Stockholders Equity Note [Line Items]
Issuance of stock (shares) | shares				11,111,112
Commissions, price per share | $ / shares				$ 17.575
Issuance of stock (shares), exercised | shares			3,333,333		1,438,356	2,876,712
Gross proceeds from public offering including exercised option | $		$ 460,000
Net proceeds from public offering including exercised option | $		$ 440,100		$ 194,800		$ 70,000
Food and Drug Administration
Stockholders Equity Note [Line Items]
Milestone payment achieved | £	£ 5
Issuance of common stock for milestone payment (in shares) | shares	257,713
Shares issued, price per share | $ / shares									$ 24.12
Accrued expenses and other current liabilities | $								$ 2,200