Quarterly Financial Information (Unaudited) - Summary of Condensed Consolidated Balance Sheets (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
Statement Of Financial Position [Abstract]
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
Total current assets	20,515	21,442	22,897	26,428	29,996	32,102	35,514	39,913
Total assets	23,055	23,056	24,967	29,673	31,994	37,648	41,000	45,110
Total current liabilities	11,200	11,226	11,882	12,464	12,466	12,744	14,189	15,289
Total shareholders' equity	$ 9,696	$ 10,888	$ 11,835	$ 15,673	$ 18,341	$ 23,858	$ 25,635	$ 29,340	$ 31,430