Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Software development
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Program development
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Program development | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Restatement Adjustment | Program development | Other assets
Property, Plant and Equipment [Line Items]
Work in process		$ (2.9)
Restatement Adjustment | Program development | Property and equipment, net
Property, Plant and Equipment [Line Items]
Work in process		$ 2.9