Cash, Cash Equivalents and Investments - Components of Cash, Cash Equivalents and Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cash	$ 266,609	$ 155,498
Money market instruments	2,464	15,933
Cash and cash equivalents	269,073	171,431
Current investments, amortized cost of $102,258 and $235,610 in 2020 and 2019, respectively, allowance for credit losses of $0 in 2020 and 2019	103,240	240,470
Non-current investments	395,125	433,452
Total	767,438	845,353
Treasury Bills [Member]
Debt Securities, Available-for-sale [Line Items]
Current investments, amortized cost of $102,258 and $235,610 in 2020 and 2019, respectively, allowance for credit losses of $0 in 2020 and 2019	35,403	92,914
Long-term investments	96,458	216,334
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Current investments, amortized cost of $102,258 and $235,610 in 2020 and 2019, respectively, allowance for credit losses of $0 in 2020 and 2019	25,160	66,680
Long-term investments	67,058	46,403
Corporate Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Current investments, amortized cost of $102,258 and $235,610 in 2020 and 2019, respectively, allowance for credit losses of $0 in 2020 and 2019	32,714	65,624
Long-term investments	203,428	146,474
Sovereign Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Current investments, amortized cost of $102,258 and $235,610 in 2020 and 2019, respectively, allowance for credit losses of $0 in 2020 and 2019	8,660	6,294
Long-term investments	3,440	16,005
Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Current investments, amortized cost of $102,258 and $235,610 in 2020 and 2019, respectively, allowance for credit losses of $0 in 2020 and 2019	1,303	4,630
Long-term investments	5,735	2,322
Certificates of Deposit [Member]
Debt Securities, Available-for-sale [Line Items]
Current investments, amortized cost of $102,258 and $235,610 in 2020 and 2019, respectively, allowance for credit losses of $0 in 2020 and 2019	0	4,328
Agency Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Long-term investments	$ 19,006	$ 5,914

Cash, cash equivalents, short term and long term investments.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as noncurrent.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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