Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
 12 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2013
Segment
Customer
Dec. 31, 2012
Customer
Dec. 31, 2011
Customer
May 31, 2013
Nov. 30, 2012
Patents
Mar. 31, 2013
License Agreements [Member]
Dec. 31, 2013
Massachusetts [Member]
Apr. 30, 2012
Massachusetts [Member]
Dec. 31, 2013
Massachusetts [Member]
Internally Developed Software [Member]
Dec. 31, 2013
Minimum [Member]
Dec. 31, 2013
Maximum [Member]
Dec. 31, 2013
Maximum [Member]
Internally Developed Software [Member]
Dec. 31, 2013
Weighted Average [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]                          
Cash equivalents maturity period Less than three months                        
Marketable securities, maturities remaining 2 years                        
Marketable securities, amortized cost $ 100,300,000 $ 100,100,000                      
Marketable securities 100,299,000 100,161,000                      
Marketable securities, unrealized gains 67,000 83,000                      
Marketable securities, unrealized losses 28,000 5,000                      
Restricted cash associated with expiration of the lease       125,000                  
Security deposit             3,300,000 3,300,000          
Bank deposit             3,500,000 3,500,000          
Bank deposit percentage             105.00% 105.00%          
Number of reporting unit 1                        
Impairments occurred 0                        
Intangible assets, estimated useful lives                 3 years 1 year 7 years 3 years  
Long-lived asset impairment 0                        
Revenue subscription period                   1 month 5 years   1 year
Accounts receivable, customers accounted description More than 10% of accounts receivable More than 10% of accounts receivable                      
Revenue, customers accounted description 10% or more of revenue 10% or more of revenue 10% or more of revenue                    
Accounts receivable, number of customers accounted 0 0                      
Revenue, number of customers accounted 0 0 0                    
Foreign currency losses 89,000 641,000 565,000                    
Uncertain tax positions 304,000 251,000 198,000                    
Advertising expense 27,800,000 23,800,000 20,500,000                    
Accumulated other comprehensive loss (1,186,000) (400,000)                      
Foreign currency translation adjustments 1,200,000 450,000                      
Unrealized (losses) gains, net of tax on available-for-sale securities 25,000 50,000                      
Number of patents involved in infringement lawsuit         3                
General and administrative expense $ 29,181,000 $ 21,338,000 $ 19,975,000     $ 1,200,000