Summary of Significant Accounting Policies - Property Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Computer hardware | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	2 years
Computer hardware | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Computer software | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	2 years
Computer software | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years