Cash, Cash Equivalents and Short-Term Investments - Cash, Cash Equivalents and Short-Term Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Cash And Cash Equivalents [Abstract]
Cash	$ 5,147	$ 6,780
Cash equivalents	1,616	3,225
Restricted cash	600	263
Restricted cash, long-term		263
Total cash and cash equivalents	7,363	10,531	$ 11,392	$ 12,859
Short-term investments	4,247	6,409
Total cash, cash equivalents and short-term investments	$ 11,610	$ 16,940