Leases - Lease cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lease cost:
Operating lease cost	$ 2.1	$ 1.9
Short-term lease cost		0.1
Sublease income	(1.1)	(1.2)
Total lease cost	$ 1.0	$ 0.8