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Investments - Investments Classified as Short-Term Available-for-Sale Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	$ 44,326	$ 73,826
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	101	102
Bankers' Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	1,722	989
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments		9,113
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	33,509	19,359
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments	$ 8,994	9,352
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments		13,298
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value of available-for-sale investments		$ 21,613

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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No definition available.

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- Definition

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+ References

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