Segment Information (Details) (USD $)	3 Months Ended										12 Months Ended
	Apr. 30, 2012	Jan. 31, 2012		Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2011		Oct. 31, 2010	Jul. 31, 2010	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
Segment Information [Abstract]
Number of operating segments	3										3
Segment Reporting Information [Line Items]
Revenue	$ 454,500,000	$ 451,100,000		$ 447,000,000	$ 430,100,000	$ 445,000,000	$ 447,900,000		$ 441,800,000	$ 407,900,000	$ 1,782,742,000	$ 1,742,551,000	$ 1,699,062,000
Direct contribution to profit											668,416,000	621,337,000	591,649,000
Shared services and administration costs											(387,997,000)	(373,189,000)	(349,057,000)
Operating income	69,700,000	78,500,000	[1]	72,000,000	60,200,000	37,600,000	69,700,000	[1]	77,700,000	63,100,000	280,419,000	248,148,000	242,592,000
Foreign exchange transaction losses											(2,261,000)	(2,188,000)	(10,883,000)
Interest expense & other, net											(6,063,000)	(14,900,000)	(31,500,000)
Income before taxes											272,095,000	231,060,000	200,209,000
Total assets	2,532,946,000					2,430,141,000					2,532,946,000	2,430,141,000	2,308,610,000
Expenditures for long lived assets											212,052,000	113,030,000	106,124,000
Depreciation and amortization											138,091,000	132,506,000	122,879,000
International Operations [Abstract]
Export sales from the United States to unaffiliated customers											151,100,000	149,800,000	140,500,000
Pretax income for consolidated operations outside the United States											171,300,000	162,800,000	133,100,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	454,500,000	451,100,000		447,000,000	430,100,000	445,000,000	447,900,000		441,800,000	407,900,000	1,782,742,000	1,742,551,000	1,699,062,000
Long-Lived Assets	1,951,352,000					1,895,131,000					1,951,352,000	1,895,131,000	1,823,752,000
United States [Member]
Segment Reporting Information [Line Items]
Revenue											893,662,000	888,833,000	865,519,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue											893,662,000	888,833,000	865,519,000
Long-Lived Assets	664,112,000					557,263,000					664,112,000	557,263,000	734,512,000
United Kingdom [Member]
Segment Reporting Information [Line Items]
Revenue											135,781,000	117,072,000	120,953,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue											135,781,000	117,072,000	120,953,000
Long-Lived Assets	1,078,704,000					1,113,946,000					1,078,704,000	1,113,946,000	889,921,000
Germany [Member]
Segment Reporting Information [Line Items]
Revenue											88,314,000	91,502,000	91,954,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue											88,314,000	91,502,000	91,954,000
Long-Lived Assets	133,078,000					146,037,000					133,078,000	146,037,000	132,783,000
Asia [Member]
Segment Reporting Information [Line Items]
Revenue											251,360,000	242,177,000	234,585,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue											251,360,000	242,177,000	234,585,000
Long-Lived Assets	8,506,000					7,239,000					8,506,000	7,239,000	3,454,000
Australia [Member]
Segment Reporting Information [Line Items]
Revenue											81,150,000	78,722,000	79,194,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue											81,150,000	78,722,000	79,194,000
Long-Lived Assets	61,092,000					64,722,000					61,092,000	64,722,000	57,447,000
Canada [Member]
Segment Reporting Information [Line Items]
Revenue											74,797,000	79,227,000	70,566,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue											74,797,000	79,227,000	70,566,000
Long-Lived Assets	5,860,000					5,924,000					5,860,000	5,924,000	5,635,000
Other Countries [Member]
Segment Reporting Information [Line Items]
Revenue											257,678,000	245,018,000	236,291,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue											257,678,000	245,018,000	236,291,000
Long-Lived Assets	0					0					0	0	0
Distribution [Member]
Segment Reporting Information [Line Items]
Shared services and administration costs											(109,079,000)	(113,010,000)	(110,858,000)
Technology Services [Member]
Segment Reporting Information [Line Items]
Shared services and administration costs											(144,418,000)	(125,766,000)	(102,634,000)
Finance [Member]
Segment Reporting Information [Line Items]
Shared services and administration costs											(45,106,000)	(45,243,000)	(47,294,000)
Other Administration [Member]
Segment Reporting Information [Line Items]
Shared services and administration costs											(89,394,000)	(89,170,000)	(88,271,000)
Scientific, Technical, Medical and Scholarly [Member]
Segment Reporting Information [Line Items]
Revenue											1,040,727,000	998,902,000	986,683,000
Direct contribution to profit											452,274,000	424,797,000	405,241,000
Total assets	1,444,114,000					1,486,052,000					1,444,114,000	1,486,052,000	1,415,979,000
Expenditures for long lived assets											24,454,000	24,636,000	21,960,000
Depreciation and amortization											56,335,000	54,423,000	52,215,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue											1,040,727,000	998,902,000	986,683,000
Professional/Trade [Member]
Segment Reporting Information [Line Items]
Revenue											433,658,000	437,088,000	429,988,000
Direct contribution to profit											111,898,000	95,496,000	100,196,000
Total assets	548,751,000					465,752,000					548,751,000	465,752,000	469,273,000
Expenditures for long lived assets											103,934,000	20,881,000	23,325,000
Depreciation and amortization											34,734,000	34,954,000	32,191,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue											433,658,000	437,088,000	429,988,000
Global Education [Member]
Segment Reporting Information [Line Items]
Revenue											308,357,000	306,561,000	282,391,000
Direct contribution to profit											104,244,000	101,044,000	86,212,000
Total assets	156,286,000					157,822,000					156,286,000	157,822,000	156,676,000
Expenditures for long lived assets											20,729,000	21,545,000	18,449,000
Depreciation and amortization											29,792,000	27,672,000	25,125,000
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue											308,357,000	306,561,000	282,391,000
Corporate/Shared Services [Member]
Segment Reporting Information [Line Items]
Total assets	383,795,000					320,515,000					383,795,000	320,515,000	266,682,000
Expenditures for long lived assets											62,935,000	45,968,000	42,390,000
Depreciation and amortization											$ 17,230,000	$ 15,457,000	$ 13,348,000

[1] In the third quarter of fiscal year 2011, the Company recorded a $9.3 million bad debt provision ($6.0 million after taxes), or $0.10 per diluted share, related to the Company's customer, Borders Group, Inc. ("Borders"). On February 16, 2011, Borders filed a petition for reorganization relief under Chapter 11 of the U.S. Bankruptcy code.