Stock-Based Compensation Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,449	$ 1,665	$ 4,447	$ 4,552
Product and content development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	382	536	1,451	1,711
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	338	362	1,065	1,179
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 729	$ 767	$ 1,931	$ 1,662