Summary of Significant Accounting Policies - Performance Obligations (Details) - Machinio - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01 $ in Millions	3 Months Ended
	Dec. 31, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	$ 2.8
Remaining performance obligation, period	1 year