The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Formation and Business of the Company - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Jun. 30, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Formation and Business of the Company [Line Items]
Net loss		$ 9,607	$ 11,265	$ 10,620	$ 17,713	$ 4,311	$ 6,230	$ 11,610	$ 14,507	$ 49,205	$ 36,658	$ 31,778
Cash used in operations										5,708	14,273	$ 58,503
Accumulated deficit		$ 306,082				$ 257,844				$ 306,082	$ 257,844
1.75% Convertible Senior Notes due 2021 [Member]
Formation and Business of the Company [Line Items]
Debt instrument due year	2021									2021