Stock-based Compensation Plans and Awards - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock-based Compensation Plans and Awards
Stock-based compensation expense	$ 2,166	$ 2,519	$ 4,244	$ 4,438
Service costs
Stock-based Compensation Plans and Awards
Stock-based compensation expense	143	650	298	912
Sales and marketing
Stock-based Compensation Plans and Awards
Stock-based compensation expense	176	233	377	441
Product development
Stock-based Compensation Plans and Awards
Stock-based compensation expense	481	517	877	916
General and administrative
Stock-based Compensation Plans and Awards
Stock-based compensation expense	$ 1,366	$ 1,119	$ 2,692	$ 2,169