CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
Operating activities
Net income	$ 30,451	$ 25,909	$ 20,716
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	8,973	10,599	8,982
Impairment of long-lived assets		2,043
Provision for doubtful accounts	291	(105)	454
Deferred income taxes	(2,579)	(1,343)	(253)
Stock-based compensation	3,196	2,306	1,654
Tax benefit from exercise of stock options	1,239	1,034	2,902
Excess tax benefit from stock-based compensation	(189)	(204)	(108)
(Gain) loss on disposition of property and equipment	(11)	(51)	3
Changes in operating assets and liabilities:
Accounts receivable	(12,332)	(5,626)	3,452
Unbilled receivables and retentions	(5,068)	(3,256)	1,360
Inventories	(5,402)	(17,209)	(9,326)
Income tax receivable			3,415
Prepaid expenses and other assets	(1,678)	(543)	(172)
Accounts payable	(10,921)	10,929	(3,785)
Other liabilities	12,784	9,003	6,690
Net cash provided by operating activities	18,754	33,486	35,984
Investing activities
Acquisition of property and equipment	(14,992)	(10,173)	(10,792)
Net (purchases) sales of held-to-maturity investments	(2,575)	8,931	(114,247)
Net sales of available-for-sale investments	225	200	275
Proceeds from sale of property and equipment	13	109
Net cash used in investing activities	(17,329)	(933)	(124,764)
Financing activities
Excess tax benefit from stock-based compensation	189	204	108
Exercise of stock options	565	619	836
Net cash provided by financing activities	754	823	944
Net increase (decrease) in cash and cash equivalents	2,179	33,376	(87,836)
Cash and cash equivalents at beginning of year	62,041	28,665	116,501
Cash and cash equivalents at end of year	64,220	62,041	28,665
Cash paid during the year for:
Income taxes	13,104	9,873	104
Non-cash investing activities
Unrealized gains (losses) on long-term investments recorded in other comprehensive income (loss), net of deferred tax benefit of $56, $16 and $143, respectively	$ 90	$ (24)	$ (223)