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Long-Lived Assets - Textbook Library (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Property, Plant and Equipment [Line Items]      
Property and equipment, gross $ 224,417 $ 154,955  
Less accumulated depreciation and amortization (98,610) (67,596)  
Textbook library, net 34,149 0  
Print textbook depreciation expense 15,397 0 $ 0
Gain on textbook library, net   $ 0 $ 0
Textbook Library      
Property, Plant and Equipment [Line Items]      
Property and equipment, gross 47,293    
Less accumulated depreciation and amortization (13,144)    
Textbook library, net 34,149    
Print textbook depreciation expense 15,400    
Gain on textbook library, net $ (1,453)