Acquisitions - Summary of Intangible Assets Subject to Amortization Acquired (Detail) - Headway $ in Millions	Apr. 04, 2017 USD ($)
Existing Technology
Finite Lived Intangible Assets [Line Items]
Estimated Fair Value, Intangible Asset	$ 1.0
Weighted average life (in years), Intangible Assets	2 years
Publisher Relationships
Finite Lived Intangible Assets [Line Items]
Estimated Fair Value, Intangible Asset	$ 5.0
Weighted average life (in years), Intangible Assets	3 years
Advertiser Relationships
Finite Lived Intangible Assets [Line Items]
Estimated Fair Value, Intangible Asset	$ 4.8
Weighted average life (in years), Intangible Assets	5 years
MediaMath Agreement
Finite Lived Intangible Assets [Line Items]
Estimated Fair Value, Intangible Asset	$ 2.1
Weighted average life (in years), Intangible Assets	9 years
Non-Compete Agreements
Finite Lived Intangible Assets [Line Items]
Estimated Fair Value, Intangible Asset	$ 1.1
Weighted average life (in years), Intangible Assets	4 years
Trade Name
Finite Lived Intangible Assets [Line Items]
Estimated Fair Value, Intangible Asset	$ 1.9
Weighted average life (in years), Intangible Assets	5 years