Summary of Significant Accounting Policies (Estimated Useful Lives of Property and Equipment) (Details)	3 Months Ended
	Mar. 31, 2019
Transportation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	Lesser of useful life or lease term
Minimum [Member] | Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	3 years
Minimum [Member] | Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	5 years
Minimum [Member] | Computer Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	3 years
Maximum [Member] | Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	5 years
Maximum [Member] | Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	7 years
Maximum [Member] | Computer Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment useful life	10 years