Background and Organization - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Net loss	$ (8,353)	$ (12,115)	$ (36,314)	$ (25,483)
Net cash used from operations			(23,883)	(20,570)
Cash and cash equivalents	$ 53,927	$ 9,429	53,927	$ 9,429	$ 14,198	$ 20,667
Proceed from private placement and equity issuances, gross			$ 65,600