Debt and Financing - Schedule of Carrying Values and Estimated Fair Values of Debt Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Book Value
Debt Instrument [Line Items]
Long-term debt, fair value	$ 1,225.4	$ 862.2
Fair Value
Debt Instrument [Line Items]
Long-term debt, fair value	1,226.6	864.7
UST Loan | Book Value
Debt Instrument [Line Items]
Long-term debt, fair value	349.2
UST Loan | Fair Value
Debt Instrument [Line Items]
Long-term debt, fair value	322.0
Term Loan | Book Value
Debt Instrument [Line Items]
Long-term debt, fair value	582.7	559.9
Term Loan | Fair Value
Debt Instrument [Line Items]
Long-term debt, fair value	611.0	559.3
Lease financing obligations | Book Value
Debt Instrument [Line Items]
Long-term debt, fair value	225.7	231.3
Lease financing obligations | Fair Value
Debt Instrument [Line Items]
Long-term debt, fair value	225.8	233.7
Second A&R CDA | Book Value
Debt Instrument [Line Items]
Long-term debt, fair value	67.8	71.0
Second A&R CDA | Fair Value
Debt Instrument [Line Items]
Long-term debt, fair value	$ 67.8	$ 71.7