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Marketable Investments - Summary of Company's Marketable Investments (Detail) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 58,224 $ 61,281
Gross Unrealized Gains 1 2
Gross Unrealized Losses (96) (136)
Market Value 58,129 61,147
Federal Agency Obligations [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,800 1,800
Gross Unrealized Losses (8) (7)
Market Value 1,792 1,793
Corporate Obligations [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 56,424 59,481
Gross Unrealized Gains 1 2
Gross Unrealized Losses (88) (129)
Market Value $ 56,337 $ 59,354