Commitments and Contingencies - Lease Cost and Terms (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Lease Cost
Operating lease cost	$ 0.6	$ 0.5	$ 1.6	$ 1.5
Short-term lease cost	0.1	0.1	0.3	0.2
Variable lease cost	0.0	0.0	0.1	0.1
Sublease income	0.0	(0.1)	0.0	(0.2)
Total lease cost	0.6	0.5	2.0	1.6
Cash paid for amounts included in the measurement of lease liabilities:
Cash paid for operating leases	$ 0.5	$ 0.4	$ 1.5	$ 1.1