Nature of Business and Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Furniture and equipment | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment useful life	7 years
Furniture and equipment | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment useful life	10 years
Computers and software | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment useful life	3 years
Computers and software | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment useful life	5 years
Buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment useful life	40 years