Commitments and Contingencies - Lease costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Lease cost
Operating lease cost	$ 1.3	$ 1.4
Variable lease cost	0.4	0.5
Operating cash flows from operating leases	$ 1.7	$ 1.3