Revenue from Contracts with Customers - Disaggregation of Revenue (Detail) - USD ($) $ 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	Dec. 31, 2017
Disaggregation of Revenue [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
Marketplaces
Disaggregation of Revenue [Line Items]
Revenue									95,757	96,321	93,020
Digital Marketing
Disaggregation of Revenue [Line Items]
Revenue									19,683	18,919	18,076
Other
Disaggregation of Revenue [Line Items]
Revenue									$ 14,519	$ 15,978	$ 11,439