v3.10.0.1
Significant Accounting Policies (Details) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Restricted Cash and Investments [Abstract]      
Restricted cash $ 0.1 $ 101.0 $ 0.0
Non-Cash Long-Lived Asset Additions      
Capital asset additions during the period $ 55.2 31.6  
Minimum      
Amortizable Intangible Assets      
Useful life of capitalized content development costs 4 years    
Maximum      
Amortizable Intangible Assets      
Useful life of capitalized content development costs 5 years    
Accounts payable and accrued expenses      
Marketing and Sales Costs      
Accrued marketing costs $ 12.3   $ 11.7
Leasehold improvements      
Non-Cash Long-Lived Asset Additions      
Capital asset additions during the period   $ 5.3  
Landlord funded leasehold improvements      
Non-Cash Long-Lived Asset Additions      
Non-cash capital expenditure $ 10.0    
Graduate Program Segment | Minimum      
Performance Obligations      
Period of contract with university clients 10 years    
Graduate Program Segment | Maximum      
Performance Obligations      
Period of contract with university clients 15 years    
Short Course Segment | Minimum      
Performance Obligations      
Period of contract with university clients 42 days    
Short Course Segment | Maximum      
Performance Obligations      
Period of contract with university clients 112 days