Leases - Components of Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating lease cost:
Amortization of right-of-use assets	$ 1.0	$ 0.7	$ 2.1	$ 1.3
Interest on lease liabilities	0.3	0.2	0.6	0.3
Total operating lease cost	$ 1.3	$ 0.9	$ 2.7	$ 1.6