Commitments and Contingencies (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Remaining aggregate obligation under the agreements with Nielsen Audio		$ 94.6
Loss contingency accrual, provision	$ 1.7

Amount charged against operating income increasing loss contingency liability, after adjustments to reduce previously estimated charges.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration