Reconciliation of Weighted Average Shares Outstanding (Details)	3 Months Ended		6 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012	Oct. 31, 2011
Reconciliation of Weighted Average Shares Outstanding [Abstract]
Weighted average shares outstanding (in shares)	60,091,000	60,721,000	59,883,000	60,789,000
Less: Unearned restricted shares (in shares)	(238,000)	(205,000)	(214,000)	(197,000)
Shares used for basic earnings per share (in shares)	59,853,000	60,516,000	59,669,000	60,592,000
Dilutive effect of stock options and other stock awards (in shares)	780,000	916,000	824,000	980,000
Shares used for diluted earnings per share (in shares)	60,633,000	61,432,000	60,493,000	61,572,000
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded for diluted EPS calculation (in shares)	2,049,562	1,027,522	2,049,562	1,027,522
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares excluded for diluted EPS calculation (in shares)	4,000	48,150	23,750	48,150