Revenue from Contract with Customer (Narrative 2) (Details) - Long-term Contract with Customer [Member] $ in Millions	Dec. 31, 2020 USD ($)
Kaplan International [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 8.8
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Supplemental Education [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 8.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months