Business Combinations, Goodwill and Intangible Assets - Weighted Average Life of Intangible Assets (Details)	9 Months Ended
	Sep. 30, 2018
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life of intangible assets	7 years 10 months 20 days
Leasehold benefits
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life of intangible assets	8 months
Developed technology
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life of intangible assets	4 years 6 months 16 days
Non-compete agreements
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life of intangible assets	11 months 18 days
Trade names and trademarks (Finite lived)
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life of intangible assets	3 years 1 month 28 days