Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Cash flows from operating activities:
Net income	$ 89,305	$ 78,713	$ 16,105
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization and depreciation	21,704	16,730	15,487
Loss on sale of discontinued operations, including $45 of stock-based compensation expense		1,222	5,688
Loss on sale/disposition of assets	150	315	285
Provisions for losses on accounts receivable	(214)	720	(465)
Change in disposal group assets and liabilities		(1,215)	5,467
Deferred income taxes	(1,463)	4,009	(1,558)
Stock-based compensation expense	8,212	4,073	2,484
Excess book deduction of stock-based compensation			(144)
Accounts receivable	(9,588)	1,505	5,089
Inventories	(23,744)	(7,702)	(9,235)
Prepaid expenses and other current assets	(1,856)	(285)	950
Income tax receivable	(1,534)	(3,384)	4,804
Accounts payable	6,468	2,602	(8,716)
Accrued payroll	2,720	3,489	3,693
Accrued taxes other than income	10	1,079	(7,151)
Accrued profit sharing	1,473	1,547	3,959
Accrued other expenses	18	(5,279)	(877)
Accrued product/municipal liability	(495)	154	(1,187)
Accrued warranty	(244)	408	2,169
Other assets	(356)	(1,930)	(189)
Other non-current liabilities	(360)	1,327	714
Net cash provided by operating activities	90,206	98,098	37,372
Cash flows from investing activities:
Proceeds from sale of business		7,500	500
Deposits on machinery and equipment	(9,269)
Receipts from note receivable	77	73	19
Payments to acquire patents and software	(243)	(102)	(164)
Proceeds from sale of property and equipment	101	1,040	26
Payments to acquire property and equipment	(53,282)	(41,421)	(13,770)
Net cash used in investing activities	(62,616)	(32,910)	(13,389)
Cash flows from financing activities:
Proceeds from loans and notes payable	101,584	1,753	1,532
Cash paid for debt issue costs	(3,791)		(1,850)
Proceeds from energy efficiency incentive programs			225
Payments on capital lease obligation	(596)	(600)
Cash paid for redemption of convertible notes			(30,000)
Payments on loans and notes payable	(45,143)	(8,195)	(1,532)
Proceeds from Economic Development Incentive Program	722		4,400
Payments to acquire treasury stock	(115,887)	(20,000)
Proceeds from exercise of options to acquire common stock, including employee stock purchase plan	3,315	4,808	1,667
Taxes paid related to restricted stock issuance	(2,068)	(209)
Excess tax benefit of stock-based compensation	2,647	1,025
Net cash used in financing activities	(59,217)	(21,418)	(25,558)
Net (decrease)/increase in cash and cash equivalents	(31,627)	43,770	(1,575)
Cash and cash equivalents, beginning of period	100,487	56,717	58,292
Cash and cash equivalents, end of period	68,860	100,487	56,717
Supplemental disclosure of cash flow information Cash paid for:
Interest	7,688	5,295	5,865
Income taxes	48,778	44,087	3,963
Supplemental Disclosure of Non-cash Investing and Financing Activities:
Capital lease obligation			$ 3,281