Pension Benefits (Net Periodic Pension Cost) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012
Pension Benefits [Abstract]
Service cost	$ 0	$ 1,326	$ 0	$ 3,892
Interest cost	1,565	1,633	4,696	4,986
Expected return on plan assets	(1,641)	(1,633)	(4,923)	(4,945)
Amortization of net loss	231	428	692	1,472
Amortization of prior service cost	0	13	0	53
Curtailment expense	0	331	0	331
Net periodic pension cost	$ 155	$ 2,098	$ 465	$ 5,789