Business Combinations, Goodwill and Intangible Assets - Weighted Average Life of Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2018
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life of intangible assets	7 years 11 months 4 days
Leasehold benefits
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life of intangible assets	4 months 28 days
Developed technology
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life of intangible assets	4 years 4 months 2 days
Non-compete agreements
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life of intangible assets	8 months 19 days
Trade names and trademarks
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average life of intangible assets	3 years 1 month 9 days