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Equity - Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				6 Months Ended
	Nov. 29, 2018	Mar. 05, 2018	Feb. 01, 2018	Jun. 30, 2019	Jun. 30, 2018
Stockholders Equity Note [Line Items]
Net proceeds from public offering				$ 837	$ 70,430
American Depositary Shares
Stockholders Equity Note [Line Items]
Issuance of stock (shares)	11,111,112		19,178,082
Over allotment option, exercisable period			30 days
Sale of stock price per share	$ 17.575		$ 3.41
Net proceeds from public offering	$ 194,800		$ 70,000
American Depositary Shares | Over-Allotment Option
Stockholders Equity Note [Line Items]
Issuance of stock (shares)			2,876,712
Issuance of stock (shares), exercised		1,438,356

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