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.

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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