Segment Information (Narrative) (Details) (USD $)	12 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
Segment Reporting Information [Line Items]
Revenues from international operations	$ 232,800,000	$ 205,800,000	$ 190,900,000
Pretax income from international operations	47,100,000	46,200,000	46,700,000
Assets	4,649,567,000	5,289,453,000	5,271,712,000
Foreign [Member]
Segment Reporting Information [Line Items]
Assets	$ 201,800,000	$ 206,300,000	$ 166,800,000