Stockholders' Equity (Summary of Stock-Based Compensation Expense Related to Employee Stock Options) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 3,112	$ 3,207	$ 5,906	$ 5,904
Cost of revenue [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	476	484	804	844
Sales and marketing expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	937	923	1,532	1,737
Product development expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	953	931	1,892	1,611
General and administrative expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 746	$ 869	$ 1,678	$ 1,712