CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Operating activities
Net income	$ 10,426	$ 30,451	$ 25,909
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	10,937	8,973	10,599
Impairment of long-lived assets			2,043
Provision for doubtful accounts	462	291	(105)
Deferred income taxes	3,851	(2,579)	(1,343)
Change in fair value of conversion feature of convertible bonds	(6,173)
Stock-based compensation	3,470	3,196	2,306
Tax benefit from exercise of stock options	1,606	1,239	1,034
Excess tax benefit from stock-based compensation		(189)	(204)
Loss (gain) on disposition of property and equipment	18	(11)	(51)
Changes in operating assets and liabilities:
Accounts receivable	36,185	(12,332)	(5,626)
Unbilled receivables and retentions	15,730	(5,068)	(3,256)
Inventories	(19,022)	(5,402)	(17,209)
Income tax receivable	(11,777)
Prepaid expenses and other assets	(317)	(1,678)	(543)
Accounts payable	(4,069)	(10,921)	10,929
Other liabilities	(17,320)	12,784	9,003
Net cash provided by operating activities	24,007	18,754	33,486
Investing activities
Acquisition of property and equipment	(11,834)	(14,992)	(10,173)
Net redemptions (purchases) of held-to-maturity investments	2,014	(2,575)	8,931
Acquisition of intangible assets	(850)
Purchases of available-for-sale investments	(3,037)
Sales of available-for-sale investments	600	225	200
Proceeds from sale of property and equipment		13	109
Net cash used in investing activities	(13,107)	(17,329)	(933)
Financing activities
Excess tax benefit from stock-based compensation		189	204
Tax withholding payment related to net settlement of equity awards	(77)
Exercise of stock options	289	565	619
Net cash provided by financing activities	212	754	823
Net increase in cash and cash equivalents	11,112	2,179	33,376
Cash and cash equivalents at beginning of year	64,220	62,041	28,665
Cash and cash equivalents at end of year	75,332	64,220	62,041
Cash paid during the year for:
Income taxes	15,262	13,104	9,873
Non-cash activities
Unrealized (loss) gain on long-term investments recorded in accumulated other comprehensive loss, net of deferred taxes of $37, $56 and $16, respectively	(11)	90	(24)
Reclassification from share-based liability compensation to equity	$ 401