Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Revenue recognition
Amounts recorded as revenues and school operating expenses	$ 81.4	$ 75.1	$ 221.0	$ 212.5
Reduction in school operating losses included in the entity's revenue	$ 18.7	$ 12.5	$ 50.2	$ 40.8
Minimum
Revenue recognition
Duration of contracts providing access to curriculum via the entity's Web site			1 year
Maximum
Revenue recognition
Duration of contracts providing access to curriculum via the entity's Web site			2 years