Leases - Lease Expense and Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lease expense
Amortization of finance lease right of use assets	$ 6.3	$ 4.9
Interest on finance lease liabilities	2.5	3.3
Capital lease expense			$ 7.7
Operating lease expense	5.4	5.5	5.6
Short-term lease expense	0.3	0.6	1.5
Lease expense	14.5	14.3	14.8
Other information
Operating cash flows from finance/capital leases	2.5	3.3	7.7
Operating cash flows from operating leases	6.7	6.0	$ 6.5
Financing cash flows from finance leases	6.3	4.9
Right-of-use asset obtained in exchange for finance lease liabilities	22.8	27.2
Right of use assets obtained in exchange for operating lease liabilities	$ 0.0	$ 49.0
Weighted average remaining lease term - finance leases	41 years 6 months	31 years 6 months
Weighted average remaining lease term - operating leases	13 years	12 years 10 months 24 days
Weighted average discount rate - finance leases	4.90%	6.70%
Weighted average discount rate - operating leases	3.40%	4.40%