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Fair Value Measurements - Summary of Fair Value Measurements of Company's Financial Assets (Detail) - Fair Value, Recurring [Member] - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Assets:    
Assets at fair value $ 172,339 $ 197,185
Level 1 [Member]    
Assets:    
Assets at fair value 70,129 68,561
Level 2 [Member]    
Assets:    
Assets at fair value 102,210 128,624
Money Market Funds [Member]    
Assets:    
Assets at fair value 70,129 68,561
Money Market Funds [Member] | Level 1 [Member]    
Assets:    
Assets at fair value 70,129 68,561
Corporate Bonds [Member]    
Assets:    
Assets at fair value 46,067 58,410
Corporate Bonds [Member] | Level 2 [Member]    
Assets:    
Assets at fair value 46,067 58,410
Commercial Paper [Member]    
Assets:    
Assets at fair value 41,787 65,330
Commercial Paper [Member] | Level 2 [Member]    
Assets:    
Assets at fair value 41,787 65,330
Asset-Backed Securities [Member]    
Assets:    
Assets at fair value 14,356 4,884
Asset-Backed Securities [Member] | Level 2 [Member]    
Assets:    
Assets at fair value $ 14,356 $ 4,884