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Marketable Investments - Summary of Gross Unrealized Losses and Market Value of Available-for-Sale Securities with Unrealized Losses (Detail) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Available for sale securities, Less Than 12 Months, Market Value $ 55,675 $ 55,440
Available for sale securities, Less Than 12 Months, Unrealized Losses 106 136
Available for sale securities, 12 Months or Greater, Market Value 1,000  
Available for sale securities, 12 Months or Greater, Unrealized Losses 1  
Federal Agency Obligations [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available for sale securities, Less Than 12 Months, Market Value 1,795 1,793
Available for sale securities, Less Than 12 Months, Unrealized Losses 5 7
Corporate Obligations [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available for sale securities, Less Than 12 Months, Market Value 53,880 53,647
Available for sale securities, Less Than 12 Months, Unrealized Losses 101 $ 129
Available for sale securities, 12 Months or Greater, Market Value 1,000  
Available for sale securities, 12 Months or Greater, Unrealized Losses $ 1