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Investments (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Short-term investments    
Fair Value $ 37.2 $ 10.0
Long-term investments    
Cost Basis 10.3 21.4
Certificates of deposit    
Short-term investments    
Cost Basis 37.2 10.0
Unrealized Gain 0.0 0.0
Fair Value 37.2 10.0
Assets held in rabbi trusts    
Long-term investments    
Cost Basis 5.2 5.5
Unrealized Gain 1.4 0.7
Fair Value $ 6.6 $ 6.2