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Long-Term Investments - Summary of Available-for-Sale Securities (Detail) - Failed Auction Security [Member] - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]    
Cost $ 3,000 $ 3,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses 474 475
Estimated Fair Value $ 2,526 $ 2,525