Segment Information - Schedule of segment reporting information (Details) $ in Millions		3 Months Ended				9 Months Ended
		Feb. 28, 2017 USD ($)		Feb. 29, 2016 USD ($)		Feb. 28, 2017 USD ($) segment		Feb. 29, 2016 USD ($)		May 31, 2016 USD ($)	May 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment						3
Revenues		$ 336.2		$ 366.0		$ 1,242.0		$ 1,159.0
Bad debt expense		1.6		3.1		9.3		8.9
Depreciation and amortization		15.0	[1]	16.0	[2]	45.8	[1]	50.9	[1]
Asset impairments		0.0		6.9		0.0		6.9
Segment operating income (loss)		(23.6)		(16.4)		24.7		9.2
Segment assets		1,847.2		1,760.1		1,847.2		1,760.1
Goodwill		116.2		116.2		116.2		116.2		$ 116.2	$ 116.3
Expenditures for long-lived assets including royalty advances		34.1		23.6		97.0		63.8
Long-lived assets		695.6		674.0		$ 695.6		674.0
Children's Book Publishing and Distribution
Segment Reporting Information [Line Items]
Number of operating segments | segment						3
Revenues		199.0		219.8		$ 769.3		701.2
Bad debt expense		0.1		1.3		3.3		3.8
Depreciation and amortization		5.3	[1]	6.0	[2]	16.6	[1]	20.4	[1]
Asset impairments	[2]			0.0				0.0
Segment operating income (loss)		6.3		8.2		91.2		62.6
Segment assets		478.4		471.4		478.4		471.4
Goodwill		40.9		40.9		40.9		40.9
Expenditures for long-lived assets including royalty advances		14.9		11.3		52.2		31.6
Long-lived assets		146.9		144.7		$ 146.9		144.7
Education
Segment Reporting Information [Line Items]
Number of operating segments | segment						2
Revenues		60.1		63.9		$ 186.4		186.7
Bad debt expense		0.4		0.5		0.9		1.7
Depreciation and amortization		2.1	[1]	3.1	[2]	6.2	[1]	9.8	[1]
Asset impairments	[2]			6.9				6.9
Segment operating income (loss)		3.5		(2.4)		7.8		3.7
Segment assets		158.8		153.4		158.8		153.4
Goodwill		65.4		65.4		65.4		65.4
Expenditures for long-lived assets including royalty advances		2.8		3.1		7.8		6.6
Long-lived assets		83.7		82.1		83.7		82.1
Overhead
Segment Reporting Information [Line Items]
Revenues	[2]	0.0		0.0		0.0		0.0
Bad debt expense	[2]	0.0		0.0		0.0		0.0
Depreciation and amortization	[1],[2]	6.0		5.0		17.4		14.7
Asset impairments	[1],[2]			0.0				0.0
Segment operating income (loss)	[2]	(29.5)		(20.5)		(90.8)		(64.2)
Segment assets	[2]	948.7		879.1		948.7		879.1
Goodwill	[2]	0.0		0.0		0.0		0.0
Expenditures for long-lived assets including royalty advances	[2]	13.9		6.9		28.5		15.1
Long-lived assets	[2]	398.6		380.2		398.6		380.2
Total Domestic
Segment Reporting Information [Line Items]
Revenues		259.1		283.7		955.7		887.9
Bad debt expense		0.5		1.8		4.2		5.5
Depreciation and amortization		13.4	[1]	14.1	[2]	40.2	[1]	44.9	[1]
Asset impairments				6.9				6.9
Segment operating income (loss)		(19.7)		(14.7)		8.2		2.1
Segment assets		1,585.9		1,503.9		1,585.9		1,503.9
Goodwill		106.3		106.3		106.3		106.3
Expenditures for long-lived assets including royalty advances		31.6		21.3		88.5		53.3
Long-lived assets		629.2		607.0		$ 629.2		607.0
International
Segment Reporting Information [Line Items]
Number of operating segments | segment						3
Revenues		77.1		82.3		$ 286.3		271.1
Bad debt expense		1.1		1.3		5.1		3.4
Depreciation and amortization		1.6	[1]	1.9	[2]	5.6	[1]	6.0	[1]
Asset impairments	[2]			0.0				0.0
Segment operating income (loss)		(3.9)		(1.7)		16.5		7.1
Segment assets		261.3		256.2		261.3		256.2
Goodwill		9.9		9.9		9.9		9.9
Expenditures for long-lived assets including royalty advances		2.5		2.3		8.5		10.5
Long-lived assets		$ 66.4		$ 67.0		$ 66.4		$ 67.0

[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.