Stock-based Compensation Plans and Awards - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation included in net loss	$ 1,680	$ 1,559	$ 6,118	$ 5,683
Accelerated compensation cost			800
Service Costs
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation included in net loss	142	182	1,054	806
Sales and Marketing
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation included in net loss	145	159	586	511
Product Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation included in net loss	290	397	1,206	1,576
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation included in net loss	$ 1,103	$ 821	$ 3,272	$ 2,790