Description of Business, Basis of Presentation and Summary of Significant Accounting Policies - Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2018
Minimum | Trademarks
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	5 years
Minimum | Domain names
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	5 years
Minimum | Mobile applications, purchased and internally developed
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	1 year
Minimum | Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	1 year
Maximum | Trademarks
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	10 years
Maximum | Domain names
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	10 years
Maximum | Mobile applications, purchased and internally developed
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	5 years
Maximum | Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	10 years