Commitments and Contingencies - Lease Cost and Terms (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Lease Cost
Operating lease cost	$ 0.6	$ 0.5
Short-term lease cost (2)	0.2	0.1
Total lease cost	0.8	0.5
Cash paid for amounts included in the measurement of lease liabilities:
Cash paid for operating leases	0.6	0.4
Variable lease cost	0.1	0.1
Sublease income	$ 0.1	$ 0.1