Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Quarterly Financial Information Disclosure [Abstract]
Net revenues	$ 15,993	$ 14,595	$ 15,002	$ 17,448	$ 16,031	$ 4,469	$ 3,893	$ 3,465	$ 63,038	$ 27,859
Net loss	$ (14,263)	$ (10,370)	$ (12,387)	$ (14,883)	$ (9,747)	$ (24,168)	$ (22,675)	$ (30,385)	$ (51,903)	$ (86,975)
Net loss per share — basic and diluted	$ (0.07)	$ (0.05)	$ (0.07)	$ (0.08)	$ (0.06)	$ (0.16)	$ (0.16)	$ (0.25)	$ (0.27)	$ (0.60)
Weighted average common shares used to compute net loss per share — basic and diluted	206,689	199,906	188,054	187,434	161,397	153,597	140,054	120,911	195,584	144,136