Marketable Securities - Schedule of Marketable Securities (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Market value, available for sale securities, current	$ 2.1	$ 2.5
Market value, available for sale securities, noncurrent	6.2	4.8
Non Current Assets
Schedule Of Available For Sale Securities [Line Items]
Market value, available for sale securities, noncurrent	6.2	4.8
Cost basis	6.2	5.2
Unrealized gains (losses), net	0.0	(0.4)
Current Assets
Schedule Of Available For Sale Securities [Line Items]
Cost basis	2.1	2.5
Unrealized gains (losses), net	$ 0.0	$ 0.0

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of investment in marketable security, classified as current.

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Amount of unrealized gain (loss) on investment in marketable security.

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