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Marketable Securities and Fair Value Measurements - Securities in Unrealized Loss Position (Details) - USD ($)
Mar. 31, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Continuous loss position, fair value $ 58,922,000 $ 53,351,000
Continuous loss position, Unrealized losses (60,000) (64,000)
Continuous loss position, fair value, more than 12 months 0  
Certificates of deposit    
Schedule of Available-for-sale Securities [Line Items]    
Continuous loss position, fair value 3,493,000  
Continuous loss position, Unrealized losses (7,000)  
Corporate securities    
Schedule of Available-for-sale Securities [Line Items]    
Continuous loss position, fair value 32,236,000 28,537,000
Continuous loss position, Unrealized losses (32,000) (42,000)
U.S. Treasury and agency securities    
Schedule of Available-for-sale Securities [Line Items]    
Continuous loss position, fair value 5,181,000 5,176,000
Continuous loss position, Unrealized losses (10,000) (14,000)
Commercial paper    
Schedule of Available-for-sale Securities [Line Items]    
Continuous loss position, fair value 5,482,000 8,974,000
Continuous loss position, Unrealized losses 0 (2,000)
Asset-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Continuous loss position, fair value 12,530,000 10,664,000
Continuous loss position, Unrealized losses $ (11,000) $ (6,000)