Segment Information - Schedule of segment reporting information (Details)	3 Months Ended		9 Months Ended
	Feb. 28, 2019 USD ($)	Feb. 28, 2018 USD ($)	Feb. 28, 2019 USD ($) segment	Feb. 28, 2018 USD ($)	May 31, 2018 USD ($)	May 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Revenues	$ 360,100,000	$ 344,700,000	$ 1,183,200,000	$ 1,132,200,000
Bad debt expense	1,600,000	1,700,000	5,700,000	7,900,000
Depreciation and amortization	20,500,000	17,000,000	60,300,000	48,300,000
Asset impairments	0	4,300,000	0	11,000,000
Segment operating income (loss)	(21,400,000)	(23,700,000)	(7,000,000)	(18,300,000)
Segment assets	2,023,100,000	1,833,700,000	2,023,100,000	1,833,700,000
Goodwill	119,100,000	119,100,000	119,100,000	119,100,000	$ 119,200,000	$ 118,900,000
Expenditures for other non-current assets	40,800,000	57,600,000	129,900,000	146,500,000
Other non-current assets	865,800,000	793,700,000	$ 865,800,000	793,700,000
Children's Book Publishing and Distribution
Segment Reporting Information [Line Items]
Number of operating segments | segment			3
Revenues	218,000,000	201,600,000	$ 731,600,000	684,200,000
Bad debt expense	800,000	700,000	3,200,000	3,400,000
Asset impairments				0
Segment assets	585,200,000	503,700,000	585,200,000	503,700,000
Goodwill	40,900,000	40,900,000	40,900,000	40,900,000
Expenditures for other non-current assets	17,300,000	17,700,000	48,300,000	45,900,000
Other non-current assets	170,400,000	155,200,000	$ 170,400,000	155,200,000
Education
Segment Reporting Information [Line Items]
Number of operating segments | segment			2
Revenues	60,300,000	59,500,000	$ 179,700,000	171,400,000
Bad debt expense	500,000	400,000	1,200,000	1,400,000
Asset impairments				0
Segment assets	173,600,000	170,200,000	173,600,000	170,200,000
Goodwill	68,200,000	68,200,000	68,200,000	68,200,000
Expenditures for other non-current assets	5,500,000	4,500,000	15,600,000	11,500,000
Other non-current assets	112,300,000	96,500,000	112,300,000	96,500,000
Overhead
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Bad debt expense	0	0	0	0
Asset impairments				11,000,000
Segment assets	977,900,000	886,100,000	977,900,000	886,100,000
Goodwill	0	0	0	0
Expenditures for other non-current assets	15,300,000	29,700,000	55,900,000	78,400,000
Other non-current assets	502,800,000	466,500,000	502,800,000	466,500,000
Total Domestic
Segment Reporting Information [Line Items]
Revenues	278,300,000	261,100,000	911,300,000	855,600,000
Bad debt expense	1,300,000	1,100,000	4,400,000	4,800,000
Asset impairments				11,000,000
Segment assets	1,736,700,000	1,560,000,000	1,736,700,000	1,560,000,000
Goodwill	109,100,000	109,100,000	109,100,000	109,100,000
Expenditures for other non-current assets	38,100,000	51,900,000	119,800,000	135,800,000
Other non-current assets	785,500,000	718,200,000	$ 785,500,000	718,200,000
International
Segment Reporting Information [Line Items]
Number of operating segments | segment			3
Revenues	81,800,000	83,600,000	$ 271,900,000	276,600,000
Bad debt expense	300,000	600,000	1,300,000	3,100,000
Asset impairments				0
Segment assets	286,400,000	273,700,000	286,400,000	273,700,000
Goodwill	10,000,000	10,000,000	10,000,000	10,000,000
Expenditures for other non-current assets	2,700,000	5,700,000	10,100,000	10,700,000
Other non-current assets	80,300,000	75,500,000	80,300,000	75,500,000
Operating Segments | Children's Book Publishing and Distribution
Segment Reporting Information [Line Items]
Depreciation and amortization	5,900,000	5,800,000	17,500,000	17,000,000
Segment operating income (loss)	4,400,000	(1,000,000)	64,700,000	55,100,000
Operating Segments | Education
Segment Reporting Information [Line Items]
Depreciation and amortization	2,600,000	1,900,000	6,700,000	5,400,000
Segment operating income (loss)	300,000	(100,000)	(6,300,000)	(8,700,000)
Operating Segments | Overhead
Segment Reporting Information [Line Items]
Depreciation and amortization	10,400,000	7,500,000	31,100,000	20,700,000
Segment operating income (loss)	(23,100,000)	(23,300,000)	(73,400,000)	(77,300,000)
Operating Segments | Total Domestic
Segment Reporting Information [Line Items]
Depreciation and amortization	18,900,000	15,200,000	55,300,000	43,100,000
Segment operating income (loss)	(18,400,000)	(24,400,000)	(15,000,000)	(30,900,000)
Operating Segments | International
Segment Reporting Information [Line Items]
Depreciation and amortization	1,600,000	1,800,000	5,000,000	5,200,000
Segment operating income (loss)	(3,000,000)	700,000	8,000,000	12,600,000
Expenditures to acquire long-lived assets	3,600,000	1,500,000	6,600,000	5,900,000
Long-lived assets	$ 35,800,000.0	36,300,000.0	$ 35,800,000.0	36,300,000.0
Legacy Building Improvements
Segment Reporting Information [Line Items]
Asset impairments		$ 4,300,000		$ 11,000,000