Revenues - Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Nov. 30, 2018	Nov. 30, 2017	Nov. 30, 2018	Nov. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues		$ 604.7	$ 598.3	$ 823.1	$ 787.5
Children's Book Publishing and Distribution
Disaggregation of Revenue [Line Items]
Revenues		417.9	413.7	513.6	482.6
Children's Book Publishing and Distribution | Book Clubs
Disaggregation of Revenue [Line Items]
Revenues		101.3	99.9	110.4	107.9
Children's Book Publishing and Distribution | Book Fairs
Disaggregation of Revenue [Line Items]
Revenues		220.7	231.0	245.9	243.1
Children's Book Publishing and Distribution | Trade
Disaggregation of Revenue [Line Items]
Revenues		95.9	82.8	157.3	131.6
Education
Disaggregation of Revenue [Line Items]
Revenues		71.5	69.0	119.4	111.9
International
Disaggregation of Revenue [Line Items]
Revenues		115.3	115.6	190.1	193.0
International | Major Markets
Disaggregation of Revenue [Line Items]
Revenues	[1]	87.9	88.6	138.2	140.3
International | Other Markets
Disaggregation of Revenue [Line Items]
Revenues	[2]	$ 27.4	$ 27.0	$ 51.9	$ 52.7

[1] Includes Canada, UK, Australia and New Zealand.

[2] Primarily includes markets in Asia.