Description of Business, Basis of Presentation, and Summary of Significant Accounting Policies - Property, Plant and Equipment Useful Life (Details)	12 Months Ended
	Dec. 31, 2017
Data Processing Equipment and Software [Member] | Minimum [Member]
Finite Lived Intangible Assets [Line Items]
Property and equipment, Useful life	3 years
Data Processing Equipment and Software [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Property and equipment, Useful life	7 years
Leasehold Improvements [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Property and equipment, Useful life	15 years
Furniture and Fixtures [Member] | Minimum [Member]
Finite Lived Intangible Assets [Line Items]
Property and equipment, Useful life	5 years
Furniture and Fixtures [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Property and equipment, Useful life	15 years