Annual report pursuant to Section 13 and 15(d)

Marketable Securities - Marketable Available-for-Sale Securities (Detail)

v3.10.0.1
Marketable Securities - Marketable Available-for-Sale Securities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 129,727 $ 74,200
Gross Unrealized Gains 0 0
Gross Unrealized Losses (58) (44)
Estimated Fair Value 129,669 74,156
U.S. and Foreign Commercial Paper [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 51,627 35,886
Estimated Fair Value 51,627 35,886
U.S. and Foreign Corporate Debt Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 34,668 19,785
Gross Unrealized Losses (34) (25)
Estimated Fair Value 34,634 19,760
Asset-backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 25,494 11,070
Gross Unrealized Gains 0  
Gross Unrealized Losses (22) (10)
Estimated Fair Value 25,472 11,060
U.S. Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 17,938 7,459
Gross Unrealized Gains 0  
Gross Unrealized Losses (2) (9)
Estimated Fair Value $ 17,936 $ 7,450