Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2012	Jan. 31, 2011
Comprehensive Income (Loss) [Abstract]
Net income	$ 62,909	$ 45,617	$ 164,481	$ 143,320
Changes in other comprehensive income (loss):
Foreign currency translation adjustment	(21,162)	603	(53,112)	33,188
Unamortized retirement costs, net of tax	1,490	1,345	3,887	2,712
Unrealized gain (loss) on interest rate swaps, net of tax	17	1,992	(100)	4,551
Comprehensive income	43,254	49,557	115,156	183,771
Reconciliation of accumulated other comprehensive income [Abstract]
Foreign currency translation adjustment, beginning of period	(97,758)		(65,808)
Change for the period	(21,162)	603	(53,112)	33,188
Foreign currency translation adjustment, end of period	(118,920)		(118,920)
Unamortized retirement costs, net of tax, beginning of period	(59,239)		(61,636)
Change for the period	1,490	1,345	3,887	2,712
Unamortized retirement costs, net of tax, end of period	(57,749)		(57,749)
Unrealized loss on interest rate swaps, net of tax, beginning of period	(414)		(297)
Change for the period	17		(100)
Unrealized loss on interest rate swaps, net of tax, end of period	(397)		(397)
Accumulated other comprehensive income (loss), beginning of period	(157,411)		(127,741)
Change for the period	(19,655)		(49,325)
Accumulated other comprehensive income (loss), end of period	$ (177,066)	$ (187,195)	$ (177,066)	$ (187,195)