Subsidiary Guarantors - Schedule of Consolidating Statement of Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ (11,033)	$ (11,474)	$ (11,771)	$ (40,946)
Other comprehensive income (loss), net of taxes:
Unrealized gain (loss) resulting from changes in fair value of derivative instruments	533	(11)	(35)	(2,810)
Realized loss (gain) on derivative instruments reclassified into earnings	310	149	655	4,139
Unrealized gain (loss) resulting from changes in fair value of marketable securities	(8)	(11)	10	4
Other comprehensive income (loss)	835	127	630	1,333
Comprehensive income (loss)	(10,198)	(11,347)	(11,141)	(39,613)
Less: Comprehensive income (loss) attributable to noncontrolling interests	(283)	(67)	(490)	(199)
Comprehensive income (loss) attributable to common stockholders	(9,915)	(11,280)	(10,651)	(39,414)
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(10,750)	(11,407)	(11,281)	(40,747)
Other comprehensive income (loss), net of taxes:
Unrealized gain (loss) resulting from changes in fair value of derivative instruments				(1,257)
Realized loss (gain) on derivative instruments reclassified into earnings				3,625
Other comprehensive income (loss)				2,368
Comprehensive income (loss)	(10,750)	(11,407)	(11,281)	(38,379)
Comprehensive income (loss) attributable to common stockholders	(10,750)	(11,407)	(11,281)	(38,379)
Guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(182)	(6,981)	20,889	(10,754)
Other comprehensive income (loss), net of taxes:
Unrealized gain (loss) resulting from changes in fair value of marketable securities	(8)	(11)	10	4
Other comprehensive income (loss)	(8)	(11)	10	4
Comprehensive income (loss)	(190)	(6,992)	20,899	(10,750)
Comprehensive income (loss) attributable to common stockholders	(190)	(6,992)	20,899	(10,750)
Non-Guarantors [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(179)	(1,566)	(1,527)	(3,769)
Other comprehensive income (loss), net of taxes:
Unrealized gain (loss) resulting from changes in fair value of derivative instruments	533	(11)	(35)	(1,553)
Realized loss (gain) on derivative instruments reclassified into earnings	310	149	655	514
Other comprehensive income (loss)	843	138	620	(1,039)
Comprehensive income (loss)	664	(1,428)	(907)	(4,808)
Less: Comprehensive income (loss) attributable to noncontrolling interests	(283)	(67)	(490)	(199)
Comprehensive income (loss) attributable to common stockholders	947	(1,361)	(417)	(4,609)
Elimination [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	78	8,480	(19,852)	14,324
Other comprehensive income (loss), net of taxes:
Comprehensive income (loss)	78	8,480	(19,852)	14,324
Comprehensive income (loss) attributable to common stockholders	$ 78	$ 8,480	$ (19,852)	$ 14,324

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount after tax of (increase) decrease in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to noncontrolling interests. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount after tax and reclassification adjustments, of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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