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Equity - Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Nov. 29, 2018	Mar. 05, 2018	Feb. 01, 2018	Dec. 31, 2018	Dec. 31, 2016
Stockholders Equity Note [Line Items]
Net proceeds from public offering				$ 264,840	$ 64,613
American Depositary Shares
Stockholders Equity Note [Line Items]
Issuance of stock (shares)	11,111,112		19,178,082
Sale of stock price per share	$ 17.575		$ 3.41
Net proceeds from public offering	$ 194,800		$ 70,000
Over allotment option, exercisable period			30 days
American Depositary Shares | Over-Allotment Option
Stockholders Equity Note [Line Items]
Issuance of stock (shares)			1,438,356
Issuance of stock (shares), exercised		2,876,712

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