Net Loss per Share - Schedule of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss	$ (11,856)	$ (12,833)	$ (20,018)	$ (14,418)	$ (16,900)	$ (18,428)	$ (15,478)	$ (11,026)	$ (59,125)	$ (61,832)
Denominator:
Weighted average common shares outstanding—basic and diluted	51,351,763	51,099,307	51,097,456	50,976,907	46,687,910	36,694,957	36,009,109	34,474,004	51,139,531	38,495,103
Net loss per share—basic and diluted	$ (0.23)	$ (0.25)	$ (0.39)	$ (0.28)	$ (0.36)	$ (0.50)	$ (0.43)	$ (0.32)	$ (1.16)	$ (1.61)