Consolidated Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (163)	$ (8,379)
Other comprehensive income (loss), net of taxes:
Unrealized loss resulting from changes in fair value of derivative instruments	(289)	(2,083)
Realized loss on derivative instruments reclassified into earnings	164	44
Unrealized loss resulting from changes in fair value of marketable securities		(6)
Other comprehensive loss	(125)	(2,045)
Comprehensive loss	(288)	(10,424)
Less: Comprehensive income (loss) attributable to noncontrolling interests	28	(8)
Comprehensive loss attributable to common stockholders	$ (316)	$ (10,416)