Stock-Based Compensation Expense (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,810,000	$ 1,583,000	$ 2,998,000	$ 2,887,000
Product and content development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	626,000	619,000	1,069,000	1,175,000
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	488,000	476,000	727,000	817,000
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 696,000	$ 488,000	$ 1,202,000	$ 895,000