Goodwill and Intangible Assets - Estimated Useful lives of the Acquired Identifiable Intangible Assets (Detail)	12 Months Ended
	Dec. 31, 2017
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives	3 years
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives	6 years
Customer Relationships [Member] | Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives	4 years
Customer Relationships [Member] | Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives	6 years
Capitalized Product Development Costs [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful lives	3 years