Accumulated Other Comprehensive Loss - Changes in accumulated other comprehensive loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Currency translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity beginning balance	$ (16.3)	$ (16.8)
Other comprehensive income (loss), net of tax, before reclassifications	(1.1)	0.3
Reclassification from accumulated other comprehensive income, current period, net of tax	0.0	0.0
Reclassification from AOCI (net tax benefit of)	0.0	0.0
Other comprehensive income (loss)	(1.1)	0.3
Equity ending balance	(17.4)	(16.5)
Unrealized loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity beginning balance	(3.4)	(0.9)
Other comprehensive income (loss), net of tax, before reclassifications	(3.4)	(1.0)
Reclassification from accumulated other comprehensive income, current period, net of tax	0.2	0.1
Reclassification from AOCI (net tax benefit of)	(0.1)	0.0
Other comprehensive income (loss)	(3.2)	(0.9)
Equity ending balance	(6.6)	(1.8)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity beginning balance	(19.7)	(17.7)
Other comprehensive income (loss), net of tax, before reclassifications	(4.5)	(0.7)
Reclassification from accumulated other comprehensive income, current period, net of tax	0.2	0.1
Reclassification from AOCI (net tax benefit of)	(0.1)	0.0
Other comprehensive income (loss)	(4.3)	(0.6)
Equity ending balance	$ (24.0)	$ (18.3)