Goodwill and Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Total gross amortizable intangible assets	$ 17,410	$ 17,410
Less accumulated amortization	(7,393)	(6,857)
Intangible assets, net	10,017	10,553
Customer and Publisher Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Total gross amortizable intangible assets	14,780	14,780
Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Total gross amortizable intangible assets	2,330	2,330
Trademark [Member]
Finite-Lived Intangible Assets [Line Items]
Total gross amortizable intangible assets	$ 300	$ 300