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Cash, Cash Equivalents and Investments - Additional Information (Detail)
12 Months Ended
Dec. 31, 2016
USD ($)
Cash Cash Equivalents And Short Term Investments [Line Items]  
Bank accounts $ 24,000,000
Available-for-sale securities, realized gains or losses 0
Investment in continuous unrealized loss position for more than one year $ 0
Maximum [Member]  
Cash Cash Equivalents And Short Term Investments [Line Items]  
Available for sale securities contractual maturity period 1 year