Fair Value Measurement - Financial Assets and Liabilities Measured at Fair Value by Hierarchy Level (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Financial Assets:
Available-for-sale investments:	$ 3.5	$ 4.5
Total financial assets	40.9	35.4
Fair Value, Measurements, Recurring
Financial Assets:
Total financial assets	3.6	4.5
Residential Mortgage-Backed Securities — Agencies \| Fair Value, Measurements, Recurring
Financial Assets:
Available-for-sale investments:	3.0	3.6
Asset-Backed and Other Securities
Financial Assets:
Available-for-sale investments:	0.5	0.9
Asset-Backed and Other Securities \| Fair Value, Measurements, Recurring
Financial Assets:
Available-for-sale investments:	0.5	0.9
Forward Contracts \| Fair Value, Measurements, Recurring
Financial Assets:
Forward contracts	0.1	0.0
Financial Liabilities:
Forward contracts	2.2	0.8
Level 2 \| Fair Value, Measurements, Recurring
Financial Assets:
Total financial assets	3.1	3.6
Level 2 \| Residential Mortgage-Backed Securities — Agencies \| Fair Value, Measurements, Recurring
Financial Assets:
Available-for-sale investments:	3.0	3.6
Level 2 \| Asset-Backed and Other Securities \| Fair Value, Measurements, Recurring
Financial Assets:
Available-for-sale investments:	0.0	0.0
Level 2 \| Forward Contracts \| Fair Value, Measurements, Recurring
Financial Assets:
Forward contracts	0.1	0.0
Financial Liabilities:
Forward contracts	2.2	0.8
Level 3 \| Fair Value, Measurements, Recurring
Financial Assets:
Total financial assets	0.5	0.9
Level 3 \| Residential Mortgage-Backed Securities — Agencies \| Fair Value, Measurements, Recurring
Financial Assets:
Available-for-sale investments:	0.0	0.0
Level 3 \| Asset-Backed and Other Securities \| Fair Value, Measurements, Recurring
Financial Assets:
Available-for-sale investments:	0.5	0.9
Level 3 \| Forward Contracts \| Fair Value, Measurements, Recurring
Financial Assets:
Forward contracts	0.0	0.0
Financial Liabilities:
Forward contracts	$ 0.0	$ 0.0

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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-Publisher FASB
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Publisher FASB
-Name Accounting Standards Codification
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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