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Cash Equivalents and Investments - Schedule of Investments (Detail) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Available-for-sale [Line Items]    
Short-Term $ 78,371 $ 21,923
Long-Term   69,699
Municipal Debt Securities [Member]    
Available-for-sale [Line Items]    
Short-Term 36,256 18,473
Long-Term   30,841
Federal Home Loan Securities [Member]    
Available-for-sale [Line Items]    
Short-Term 23,825 2,000
Long-Term   34,393
Corporate Securities [member]    
Available-for-sale [Line Items]    
Short-Term 13,823  
Certificates of Deposit [Member]    
Available-for-sale [Line Items]    
Short-Term $ 4,467 1,450
Long-Term   $ 4,465