Stockholders' Equity - Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jul. 31, 2014	Jul. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss from equity method investments		$ (977)
Loss from continuing operations before income taxes and discontinued operations	136	205
Provision for income taxes	(290)	(319)
Loss from continuing operations before discontinued operations	(154)	(114)
Commodity Hedges [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss from continuing operations before income taxes and discontinued operations		(164)
Provision for income taxes
Loss from continuing operations before discontinued operations		(164)
Commodity Hedges [Member] | Commodity Contract [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss from equity method investments		$ (164)