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Revenues - Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disaggregation of Revenue [Line Items]      
Contract with customer, liability, revenue recognized $ 32.6 $ 18.3 $ 17.0
Contract with customer, liability, revenue recognized, prior period 4.9   $ 3.4
Textbook Library      
Disaggregation of Revenue [Line Items]      
Operating lease income $ 34.6 $ 50.8