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Goodwill and Other Intangible Assets - Changes in Carrying Amount of Definite-Lived Intangible Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]      
Gross carrying value $ 113.0 $ 112.8  
Accumulated amortization (31.9) (22.1)  
Net carrying value 81.1 90.7  
Total intangible assets (excluding goodwill), gross carrying value 185.4 185.0  
Total intangible assets (excluding goodwill), net $ 153.5 162.9  
Definite-lived intangible asset, useful life 12 years    
Amortization expense $ 9.6 8.8 $ 8.0
Estimated amortization of intangibles, year one 9.6    
Estimated amortization of intangibles, year two 9.5    
Estimated amortization of intangibles, year three 9.3    
Estimated amortization of intangibles, year four 9.3    
Estimated amortization of intangibles, year five 9.3    
Estimated amortization of intangibles, thereafter 34.1    
Customer Relationships      
Finite-Lived Intangible Assets [Line Items]      
Gross carrying value [1] 108.6 108.6  
Accumulated amortization [1] (29.6) (20.5)  
Net carrying value [1] $ 79.0 88.1  
Customer Relationships | TBEI      
Finite-Lived Intangible Assets [Line Items]      
Definite-lived intangible asset, useful life 12 years    
Other Intangible Assets      
Finite-Lived Intangible Assets [Line Items]      
Gross carrying value [1] $ 4.4 4.2  
Accumulated amortization [1] (2.3) (1.6)  
Net carrying value [1] $ 2.1 $ 2.6  
Definite-lived intangible asset, useful life 8 years    
[1] Average useful life of customer relationships and other definite-lived intangible assets are estimated to be approximately 12 years and eight years, respectively. The average useful life across all definite-lived intangible assets is estimated to be approximately 12 years.