Segment Information - Schedule of segment reporting information (Details) $ in Millions		3 Months Ended
		Aug. 31, 2017 USD ($) segment		Aug. 31, 2016 USD ($)		May 31, 2017 USD ($)	May 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment		3
Revenues		$ 189.2		$ 282.7
Bad debt expense		1.9		2.9
Depreciation and amortization		15.4	[1]	15.3	[2]
Asset impairments		6.7		0.0
Segment operating income (loss)		(101.8)		(62.5)
Segment assets		1,759.6		1,774.7
Goodwill		119.2		116.3		$ 118.9	$ 116.2
Expenditures for other non-current assets (3)	[3]	45.3		39.8
Other non-current assets at 8/31/17 (3)	[3]	$ 732.4		674.9
Children's Book Publishing and Distribution
Segment Reporting Information [Line Items]
Number of operating segments | segment		3
Education
Segment Reporting Information [Line Items]
Number of operating segments | segment		2
International
Segment Reporting Information [Line Items]
Number of operating segments | segment		3
Operating Segments | Children's Book Publishing and Distribution
Segment Reporting Information [Line Items]
Revenues		$ 66.8		137.8
Bad debt expense		0.5		1.3
Depreciation and amortization		5.2	[1]	5.6	[2]
Asset impairments		0.0
Segment operating income (loss)		(58.9)		(36.2)
Segment assets		476.9		534.5
Goodwill		40.9		40.9
Expenditures for other non-current assets (3)	[3]	9.9		25.9
Other non-current assets at 8/31/17 (3)	[3]	140.2		144.6
Operating Segments | Education
Segment Reporting Information [Line Items]
Revenues		45.0		55.2
Bad debt expense		(0.1)		(0.1)
Depreciation and amortization		2.2	[1]	2.0	[2]
Asset impairments		0.0
Segment operating income (loss)		(12.5)		(4.4)
Segment assets		176.1		167.1
Goodwill		68.3		65.4
Expenditures for other non-current assets (3)	[3]	2.5		2.6
Other non-current assets at 8/31/17 (3)	[3]	94.5		83.1
Operating Segments | Overhead
Segment Reporting Information [Line Items]
Revenues	[2]	0.0		0.0
Bad debt expense	[2]	0.0		0.0
Depreciation and amortization	[1],[2]	6.3		5.7
Asset impairments	[1],[2]	6.7
Segment operating income (loss)	[2]	(27.6)		(26.1)
Segment assets	[2]	845.6		807.2
Goodwill	[2]	0.0		0.0
Expenditures for other non-current assets (3)	[2],[3]	30.8		8.5
Other non-current assets at 8/31/17 (3)	[2],[3]	429.7		382.1
Operating Segments | Total Domestic
Segment Reporting Information [Line Items]
Revenues		111.8		193.0
Bad debt expense		0.4		1.2
Depreciation and amortization		13.7	[1]	13.3	[2]
Asset impairments		6.7
Segment operating income (loss)		(99.0)		(66.7)
Segment assets		1,498.6		1,508.8
Goodwill		109.2		106.3
Expenditures for other non-current assets (3)	[3]	43.2		37.0
Other non-current assets at 8/31/17 (3)	[3]	664.4		609.8
Operating Segments | International
Segment Reporting Information [Line Items]
Revenues		77.4		89.7
Bad debt expense		1.5		1.7
Depreciation and amortization		1.7	[1]	2.0	[2]
Asset impairments		0.0
Segment operating income (loss)		(2.8)		4.2
Segment assets		261.0		265.9
Goodwill		10.0		10.0
Expenditures for other non-current assets (3)	[3]	2.1		2.8
Other non-current assets at 8/31/17 (3)	[3]	68.0		65.1
Expenditures to acquire long-lived assets		1.3		1.3
Long-lived assets		$ 33.9		$ 34.2

[1] Includes depreciation of property, plant and equipment and amortization of intangible assets and prepublication and production costs.

[2] Overhead includes all domestic corporate amounts not allocated to segments, including expenses and costs related to the management of corporate assets. Unallocated assets are principally comprised of deferred income taxes and property, plant and equipment related to the Company’s headquarters in the metropolitan New York area, its fulfillment and distribution facilities located in Missouri and its facility located in Connecticut.

[3] Other non-current assets include property, plant and equipment, prepublication, production, royalty advances, goodwill, intangible assets and investments. Expenditures for other non-current assets for the International reportable segment include expenditures for long-lived assets of $1.3 and $1.3 for the three months ended August 31, 2017 and August 31, 2016, respectively. Other non-current assets for the International reportable segment include long-lived assets of $33.9 and $34.2 as of August 31, 2017 and August 31, 2016, respectively.