Revenues - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Deferred commission	$ 2.8	$ 2.5
Recognized service revenue	10.8	9.0
Refund liability	0.1
Prepaid expenses and other current assets
Disaggregation of Revenue [Line Items]
Deferred commission	1.9	1.8
Other long-term assets
Disaggregation of Revenue [Line Items]
Deferred commission	$ 0.9	$ 0.7