CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Operating activities
Net income	$ 12,457	$ 8,966	$ 2,895
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	7,054	6,074	8,366
Loss from equity method investments	119	138	240
Impairment of available-for-sale securities		2,186
Impairment of long-lived assets	46		438
Provision for doubtful accounts	56	(178)	(106)
Losses on foreign currency transactions	284	63	580
Loss on sale of equity securities		219	209
Deferred income taxes	(52)	(2,912)	(3,382)
Gain on business acquisition	(584)
Change in fair value of conversion feature of convertible bonds			(73)
Stock-based compensation	3,709	4,562	3,768
Tax benefit from exercise of stock options		161	52
Excess tax benefit from stock-based compensation		(39)	(162)
Loss (gain) on disposition of property and equipment	37	(22)	3,661
Amortization of held-to-maturity investments	2,382	3,875	4,532
Changes in operating assets and liabilities:
Accounts receivable	(18,627)	(22,260)	(1,762)
Unbilled receivables and retentions	4,779	(1,543)	(6,427)
Inventories	(22,590)	1,928	11,285
Income tax receivable			6,584
Prepaid expenses and other assets	(1,466)	517	(339)
Accounts payable	2,843	(2,705)	5,337
Other liabilities	(946)	1,521	3,717
Net cash (used in) provided by operating activities	(10,499)	551	39,413
Investing activities
Acquisition of property and equipment	(9,862)	(6,829)	(5,279)
Equity method investment		(295)	(395)
Business acquisition, net of cash acquired	(430)
Redemptions of held-to-maturity investments	121,522	84,433	69,387
Purchases of held-to-maturity investments	(148,991)	(94,954)	(97,464)
Acquisitions of intangible assets			(150)
Proceeds from the sale of property and equipment	7	80
Sales and redemptions of available-for-sale investments	400	987	10,081
Net cash used in investing activities	(37,354)	(16,578)	(23,820)
Financing activities
Purchase and retirement of common stock		(3,756)
Principal payments of capital lease obligations	(390)	(472)
Excess tax benefit from stock-based compensation		39	162
Tax withholding payment related to net settlement of equity awards	(5)	(29)	(36)
Exercise of stock options	3,865	1,122	722
Net cash provided by (used in) financing activities	3,470	(3,096)	848
Net (decrease) increase in cash and cash equivalents	(44,383)	(19,123)	16,441
Cash and cash equivalents at beginning of period	124,287	143,410	126,969
Cash and cash equivalents at end of period	79,904	124,287	143,410
Cash paid during the period for:
Income taxes	1,804	1,576	700
Non-cash activities
Unrealized gain (loss) on investments, net of deferred tax expense (benefit) of $43, $18 and $(730) for the fiscal years ended April 30, 2017, April 30, 2016 and April 30, 2015 respectively	74	27	(1,095)
Reclassification from share-based liability compensation to equity	307	228
Forfeiture of vested stock-based compensation		86	23
Acquisitions of property and equipment financed with capital lease obligations		932
Accrued acquisition of intangible assets			$ 250
Acquisitions of property and equipment included in accounts payable	$ 729	$ 1,174