Stock-based Compensation Plans and Awards - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock-based Compensation Plans and Awards
Stock-based compensation expense	$ 2,460	$ 2,502	$ 6,590	$ 7,386
Service costs
Stock-based Compensation Plans and Awards
Stock-based compensation expense	315	189	758	515
Sales and marketing
Stock-based Compensation Plans and Awards
Stock-based compensation expense	269	292	520	760
Product development
Stock-based Compensation Plans and Awards
Stock-based compensation expense	635	603	1,791	1,762
General and administrative
Stock-based Compensation Plans and Awards
Stock-based compensation expense	$ 1,241	$ 1,418	$ 3,521	$ 4,349