Subsidiary Guarantors (Schedule of Consolidating Statements of Comprehensive Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ (11,474)	$ (24,635)	$ (40,946)	$ (28,461)
Other comprehensive income (loss), net of taxes:
Unrealized gain (loss) resulting from changes in fair value of derivative instruments, net of tax	(11)	(1,981)	(2,810)	(1,798)
Realized loss (gain) on derivative instruments reclassified into earnings, net of tax	149	109	4,139	(607)
Unrealized gain (loss) resulting from changes in fair value of marketable securities	(11)	(16)	4	(27)
Other comprehensive income (loss)	127	(1,888)	1,333	(2,432)
Comprehensive income (loss)	(11,347)	(26,523)	(39,613)	(30,893)
Less: Comprehensive income (loss) attributable to noncontrolling interest	(67)		(199)
Comprehensive income (loss) attributable to common stockholders	(11,280)	(26,523)	(39,414)	(30,893)
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(11,407)	(24,635)	(40,747)	(28,461)
Other comprehensive income (loss), net of taxes:
Unrealized gain (loss) resulting from changes in fair value of derivative instruments, net of tax		(2,474)	(1,257)	(2,371)
Realized loss (gain) on derivative instruments reclassified into earnings, net of tax			3,625	(78)
Unrealized gain (loss) resulting from changes in fair value of marketable securities
Other comprehensive income (loss)		(2,474)	2,368	(2,449)
Comprehensive income (loss)	(11,407)		(38,379)
Less: Comprehensive income (loss) attributable to noncontrolling interest
Comprehensive income (loss) attributable to common stockholders	(11,407)	(27,109)	(38,379)	(30,910)
Guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(6,981)	(4,849)	(10,754)	(489)
Other comprehensive income (loss), net of taxes:
Unrealized gain (loss) resulting from changes in fair value of derivative instruments, net of tax
Realized loss (gain) on derivative instruments reclassified into earnings, net of tax
Unrealized gain (loss) resulting from changes in fair value of marketable securities	(11)	(16)	4	(27)
Other comprehensive income (loss)	(11)	(16)	4	(27)
Comprehensive income (loss)	(6,992)		(10,750)
Less: Comprehensive income (loss) attributable to noncontrolling interest
Comprehensive income (loss) attributable to common stockholders	(6,992)	(4,865)	(10,750)	(462)
Non-Guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(1,566)	(17,091)	(3,769)	(20,874)
Other comprehensive income (loss), net of taxes:
Unrealized gain (loss) resulting from changes in fair value of derivative instruments, net of tax	(11)	493	(1,553)	573
Realized loss (gain) on derivative instruments reclassified into earnings, net of tax	149	109	514	(529)
Unrealized gain (loss) resulting from changes in fair value of marketable securities
Other comprehensive income (loss)	138	602	(1,039)	44
Comprehensive income (loss)	(1,428)		(4,808)
Less: Comprehensive income (loss) attributable to noncontrolling interest	(67)		(199)
Comprehensive income (loss) attributable to common stockholders	(1,361)	(16,489)	(4,609)	(20,830)
Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	8,480	21,940	14,324	20,385
Other comprehensive income (loss), net of taxes:
Unrealized gain (loss) resulting from changes in fair value of derivative instruments, net of tax
Realized loss (gain) on derivative instruments reclassified into earnings, net of tax
Unrealized gain (loss) resulting from changes in fair value of marketable securities
Other comprehensive income (loss)
Comprehensive income (loss)	8,480		14,324
Less: Comprehensive income (loss) attributable to noncontrolling interest
Comprehensive income (loss) attributable to common stockholders	$ 8,480	$ 21,940	$ 14,324	$ 20,385

The change in equity [net assets] of a business enterprise during a period from transactions and other events and circumstances from non-owner sources which are attributable to the reporting entity. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners, but excludes any and all transactions which are directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent.

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