Segment Information - Schedule of segment reporting information (Details) $ in Millions	3 Months Ended				9 Months Ended
	Feb. 28, 2021 USD ($)	Nov. 30, 2020 USD ($)	Aug. 31, 2020 USD ($)	Feb. 29, 2020 USD ($)	Feb. 28, 2021 USD ($) segment	Feb. 29, 2020 USD ($)	May 31, 2020 USD ($)	May 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment					3
Revenues	$ 277.5			$ 373.3	$ 898.9	$ 1,203.1
Bad debt expense	(0.1)	$ 2.1	$ 1.4	3.0	3.4	7.3
Depreciation and amortization	22.2			22.7	68.3	67.8
Asset impairments and write downs	10.9			40.0	10.9	40.0
Segment operating income (loss)	(24.2)			(60.0)	(32.4)	(42.3)
Segment assets	2,035.0			1,948.4	2,035.0	1,948.4
Goodwill	126.0			125.3	126.0	125.3	$ 124.9	$ 125.2
Expenditures for other non-current assets	24.3			41.7	77.8	110.9
Other non-current assets	864.0			881.8	$ 864.0	881.8
Children's Book Publishing and Distribution
Segment Reporting Information [Line Items]
Number of operating segments | segment					3
Revenues	141.3			220.2	$ 472.5	743.4
Bad debt expense	(0.5)			1.2	(0.4)	2.8
Asset impairments and write downs				0.0		0.0
Segment assets	562.0			594.1	562.0	594.1
Goodwill	47.6			47.1	47.6	47.1
Expenditures for other non-current assets	9.3			11.5	31.0	40.2
Other non-current assets	168.7			183.0	$ 168.7	183.0
Education
Segment Reporting Information [Line Items]
Number of operating segments | segment					3
Revenues	66.3			74.3	$ 187.4	192.6
Bad debt expense	0.3			0.7	1.7	1.5
Asset impairments and write downs				0.0		0.0
Segment assets	206.8			208.5	206.8	208.5
Goodwill	68.3			68.2	68.3	68.2
Expenditures for other non-current assets	3.7			5.4	10.0	15.0
Other non-current assets	124.1			123.1	124.1	123.1
Overhead
Segment Reporting Information [Line Items]
Revenues	0.0			0.0	0.0	0.0
Bad debt expense	0.0			0.0	0.0	0.0
Asset impairments and write downs				40.0		40.0
Segment assets	953.3			853.9	953.3	853.9
Goodwill	0.0			0.0	0.0	0.0
Expenditures for other non-current assets	8.8			19.4	27.7	37.6
Other non-current assets	482.9			499.1	482.9	499.1
Total Domestic
Segment Reporting Information [Line Items]
Revenues	207.6			294.5	659.9	936.0
Bad debt expense	(0.2)			1.9	1.3	4.3
Asset impairments and write downs				40.0
Segment assets	1,722.1			1,656.5	1,722.1	1,656.5
Goodwill	115.9			115.3	115.9	115.3
Expenditures for other non-current assets	21.8			36.3	68.7	92.8
Other non-current assets	775.7			805.2	$ 775.7	805.2
International
Segment Reporting Information [Line Items]
Number of operating segments | segment					3
Revenues	69.9			78.8	$ 239.0	267.1
Bad debt expense	0.1			1.1	2.1	3.0
Asset impairments and write downs				0.0
Goodwill	10.1			10.0	10.1	10.0
Expenditures for other non-current assets	2.5			5.4	9.1	18.1
Expenditures to acquire long-lived assets	1.4			4.3	4.9	14.2
Long-lived assets	46.5			44.1	46.5	44.1
Operating Segments | Children's Book Publishing and Distribution
Segment Reporting Information [Line Items]
Depreciation and amortization	6.2			6.7	19.4	19.9
Asset impairments and write downs	2.4				2.4
Segment operating income (loss)	(6.6)			2.2	1.9	70.1
Operating Segments | Education
Segment Reporting Information [Line Items]
Depreciation and amortization	3.1			3.3	9.5	9.8
Asset impairments and write downs	0.0				0.0
Segment operating income (loss)	10.1			9.8	19.8	2.6
Operating Segments | Overhead
Segment Reporting Information [Line Items]
Depreciation and amortization	11.2			10.8	34.6	32.7
Asset impairments and write downs	8.5				8.5
Segment operating income (loss)	(26.6)			(68.3)	(77.4)	(119.3)
Operating Segments | Total Domestic
Segment Reporting Information [Line Items]
Depreciation and amortization	20.5			20.8	63.5	62.4
Asset impairments and write downs	10.9				10.9	40.0
Segment operating income (loss)	(23.1)			(56.3)	(55.7)	(46.6)
Operating Segments | International
Segment Reporting Information [Line Items]
Depreciation and amortization	1.7			1.9	4.8	5.4
Asset impairments and write downs	0.0				0.0	0.0
Segment operating income (loss)	(1.1)			(3.7)	23.3	4.3
Segment assets	312.9			291.9	312.9	291.9
Other non-current assets	$ 88.3			$ 76.6	$ 88.3	$ 76.6