Cash and Investments - Cash, Cash Equivalents, Restricted Cash, and Short-Term Investments (Detail) - USD ($) $ in Thousands	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, 2017
Cash And Cash Equivalents [Abstract]
Cash	$ 4,092				$ 6,780
Cash equivalents	3,620				3,225
Restricted cash	600				263
Restricted cash, long-term					263
Total cash, cash equivalents and restricted cash as presented in the statement of cash flows	8,312				10,531				$ 12,859
Short-term investments	2,249				6,409
Total cash, cash equivalents, restricted cash and short-term investments	$ 10,561	$ 11,610	$ 12,560	$ 15,000	$ 16,940	$ 17,271	$ 17,861	$ 21,435