Property and Equipment - Estimated useful lives (Details)	12 Months Ended
	Dec. 31, 2018
Minimum | Computer equipment and software
Property, Plant and Equipment [Line Items]
Estimated useful life	2 years
Minimum | Buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Minimum | Furniture, fixtures, vehicles and equipment
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Minimum | Assets under capital leases
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Maximum | Computer equipment and software
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Maximum | Buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated useful life	40 years
Maximum | Furniture, fixtures, vehicles and equipment
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Maximum | Assets under capital leases
Property, Plant and Equipment [Line Items]
Estimated useful life	8 years