Commitments and Contingencies - Lease Cost and Terms (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Lease Cost
Operating lease cost	$ 0.4	$ 0.5		$ 1.0	$ 1.0
Short-term lease cost	0.1	0.0	$ 0.1	0.3	0.1
Variable lease cost	0.1	0.1		0.1	0.1
Total lease cost	0.5	0.5		1.4	1.1
Cash paid for amounts included in the measurement of lease liabilities:
Cash paid for operating leases	0.4	0.4		1.0	0.8
Sublease income	$ 0.1	$ 0.1		$ 0.1	$ 0.1