Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	2 years
Machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	10 years
Vehicles | Minimum
Property, Plant and Equipment [Line Items]
Useful life	2 years
Vehicles | Maximum
Property, Plant and Equipment [Line Items]
Useful life	5 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Useful life	2 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Useful life	5 years
Computer hardware and software | Minimum
Property, Plant and Equipment [Line Items]
Useful life	2 years
Computer hardware and software | Maximum
Property, Plant and Equipment [Line Items]
Useful life	5 years