Financial Instruments - Summary of Available-for-Sale Short-Term and Long-Term Investments (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 205.2	$ 159.2
Gross Unrealized Gains		0.1
Aggregate Fair Value	205.2	159.3
Long-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2.0
Aggregate Fair Value		2.0
Corporate Debt Securities [Member] \| Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	195.4	152.7
Gross Unrealized Gains		0.1
Aggregate Fair Value	195.4	152.8
Corporate Debt Securities [Member] \| Long-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2.0
Aggregate Fair Value		2.0
Foreign Certificates of Deposit and Time Deposits [Member] \| Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9.8	6.5
Aggregate Fair Value	$ 9.8	$ 6.5

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

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