Segment and Geographic Information - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment									1
Number of operating segments | segment									1
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue | $	$ 34,775	$ 31,678	$ 31,932	$ 31,574	$ 34,789	$ 32,324	$ 32,660	$ 31,445	$ 129,959	$ 131,218	$ 122,535
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue | $									$ 13,000	$ 12,300	$ 11,700