Operating Segments - Narrative (Detail) $ in Millions	1 Months Ended
Jul. 31, 2018 USD ($)	Dec. 31, 2018 partner_company
Segment Reporting Information [Line Items]
Partner companies not consolidated \| partner_company		21
Media Math Inc [Member]
Segment Reporting Information [Line Items]
Ownership percent sold	39.13%
Proceeds from Sale of Equity Method Investments \| $	$ 45.0

The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

Name:	us-gaap_ProceedsFromSaleOfEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration