Stock-Based Compensation Expense - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock-Based Compensation Expense
Stock-based compensation expense	$ 3,900	$ 4,007	$ 4,622
Technology and development
Stock-Based Compensation Expense
Stock-based compensation expense	931	854	907
Sales and marketing
Stock-Based Compensation Expense
Stock-based compensation expense	1,415	1,445	1,506
Sales and marketing | Non employee stock option
Stock-Based Compensation Expense
Stock-based compensation expense	0	5	15
General and administrative
Stock-Based Compensation Expense
Stock-based compensation expense	$ 1,554	$ 1,708	$ 2,209