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Fair Value Measurement - Additional Information (Detail) - USD ($) $ in Millions | Mar. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Convertible debt [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Debt instrument, interest rate, stated percentage |  |  | 2.50%
Convertible debt [Member] | Convertibles and bonds with warrants attached [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Debt instrument, interest rate, stated percentage |  |  | 2.50%
Non-convertible debt [Member] | Convertibles and bonds with warrants attached [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Debt instrument, interest rate, stated percentage |  |  | 2.50%
Fair value, inputs, level 1 [Member] | Money market funds [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Cash Equivalents, at Carrying Value | $ 82.1 | $ 61.1 |
Fair value, inputs, level 1 [Member] | Korean market government bonds [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Cash Equivalents, at Carrying Value |  | $ 61.1 | $ 25.7
Fair value, inputs, level 3 [Member] | Convertible debt [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Debt instrument, interest rate, stated percentage |  |  | 2.50%
Convertible Debt, Fair Value Disclosures |  |  | $ 325.0
Fair value, inputs, level 3 [Member] | Non-convertible debt [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Debt instrument, interest rate, stated percentage |  |  | 2.50%
Convertible Debt, Fair Value Disclosures |  |  | $ 133.5

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- Definition Amount of 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock. + References No definition available. + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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