Accumulated Other Comprehensive Loss - Changes in accumulated other comprehensive loss (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Currency translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity beginning balance	$ (16.8)	$ (19.8)
Other comprehensive income (loss), net of tax, before reclassifications	0.4	0.5
Reclassification from accumulated other comprehensive income, current period, net of tax	0.0	0.0
Reclassification from AOCI, current period, tax	0.0	0.0
Other comprehensive income (loss)	0.4	0.5
Equity ending balance	(16.4)	(19.3)
Unrealized loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity beginning balance	(0.9)	0.0
Other comprehensive income (loss), net of tax, before reclassifications	(2.8)	0.0
Reclassification from accumulated other comprehensive income, current period, net of tax	0.1	0.0
Reclassification from AOCI, current period, tax	0.0	0.0
Other comprehensive income (loss)	(2.7)	0.0
Equity ending balance	(3.6)	0.0
Accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity beginning balance	(17.7)	(19.8)
Other comprehensive income (loss), net of tax, before reclassifications	(2.4)	0.5
Reclassification from accumulated other comprehensive income, current period, net of tax	0.1	0.0
Reclassification from AOCI, current period, tax	0.0	0.0
Other comprehensive income (loss)	(2.3)	0.5
Equity ending balance	$ (20.0)	$ (19.3)