XML 53 R42.htm IDEA: XBRL DOCUMENT v3.19.2
Fair Value of Financial Instruments - Financial Assets Carried at Fair Value (Detail) - Money Market Funds - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Money market funds $ 491,413 $ 485,872
(Level 1)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Money market funds 491,413 485,872
(Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Money market funds 0 0
(Level 3)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Money market funds $ 0 $ 0