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Fair Value Measurements - Nonrecurring Fair Value Measurements (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Assets and liabilities measured at estimated fair value on a recurring basis        
Asset impairments $ 4.7 $ 18.6   $ 18.6
Nonrecurring Fair Value Measurements        
Assets and liabilities measured at estimated fair value on a recurring basis        
Asset impairments     $ 4.7