Fair-Value Measurements - Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money-market funds classified as non-current restricted investments	$ 1,055	$ 1,154
Money-market funds classified as short-term investments	124,452	57,704
Fair Value, Measurements, Recurring \| Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money-market funds classified as non-current restricted investments	1,055	1,154
Money-market funds classified as short-term investments	124,452	57,704
Total	125,507	58,858
Fair Value, Measurements, Recurring \| Level 1 \| Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money-market funds classified as non-current restricted investments	1,055	1,154
Money-market funds classified as short-term investments	124,452	57,704
Total	$ 125,507	$ 58,858

Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, 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.

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Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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