Revenues - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Deferred commission	$ 2.9	$ 2.5	$ 2.9	$ 2.5
Recognized service revenue	8.8	7.2	19.7	16.2
Refund liability	0.1	0.1	0.1	0.1
Prepaid expenses and other current assets
Disaggregation of Revenue [Line Items]
Deferred commission	2.0	1.8	2.0	1.8
Other long-term assets
Disaggregation of Revenue [Line Items]
Deferred commission	$ 0.9	$ 0.7	$ 0.9	$ 0.7