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Equity - Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			9 Months Ended
	Mar. 05, 2018	Feb. 01, 2018	Sep. 30, 2018
Stockholders Equity Note [Line Items]
Net proceeds from public offering			$ 70,007
American Depositary Shares
Stockholders Equity Note [Line Items]
Issuance of stock (shares)		19,178,082
Over allotment option, exercisable period		30 days
Sale of stock price per share		$ 3.41
Net proceeds from public offering		$ 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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