Impact of Adoption of New Accounting Standards - Statement Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 28, 2018	Jul. 29, 2017
Operating activities
Net income (loss)	$ 27,316	$ (5,882)
Gain on sale of business, net of tax expense	(8,843)
Loss from discontinued operations, net of tax	1,850	1,488
Net income (loss) from continuing operations	20,323	(4,394)
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Depreciation and amortization	1,746	1,406
Loss from equity method investments	602
Impairment of long-lived assets		9
Provision for doubtful accounts	(48)	209
Gains on foreign currency transactions	(2)	(106)
Deferred income taxes	(306)	(597)
Stock-based compensation	1,287	1,326
Amortization of held-to-maturity investments	(115)	474
Changes in operating assets and liabilities:
Accounts receivable	43,189	43,819
Unbilled receivables and retentions	(42,998)	6,234
Inventories	(4,819)	(10,224)
Income tax receivable		(3,385)
Prepaid expenses and other assets	(133)	358
Accounts payable	(9,893)	(5,504)
Other liabilities	(3,797)	(4,306)
Net cash provided by operating activities of continuing operations	5,036	25,319
Investing activities
Acquisition of property and equipment	(1,423)	(2,705)
Proceeds from sale of business	31,994
Redemptions of held-to-maturity investments	78,909	59,280
Purchases of held-to-maturity investments	(81,646)	(41,806)
Redemptions of available-for-sale investments	2,250	450
Net cash used in investing activities from continuing operations	30,084	15,219
Financing activities
Principal payments of capital lease obligations	(57)	(92)
Tax withholding payment related to net settlement of equity awards	(819)	(212)
Exercise of stock options	67	1,640
Net cash (used in) provided by financing activities from continuing operations	(809)	1,336
Discontinued operations
Operating activities of discontinued operations	(6,609)	(4,037)
Investing activities of discontinued operations	(431)	(268)
Net cash provided by (used in) discontinued operations	(7,040)	(4,305)
Net increase in cash and cash equivalents	27,271	37,569
Cash and cash equivalents at beginning of period	143,517	79,904
Cash and cash equivalents at end of period	170,788	117,473
Cash (refunds) paid, net during the period for:
Income taxes	7	1,803
Non-cash activities
Unrealized gain on investments, net of deferred tax expense of $4	57	2
Reclassification from share-based liability compensation to equity		384
Change in foreign currency translation adjustments	(20)
Acquisitions of property and equipment included in accounts payable	595	644
Effect of the Adoption of ASC Topic 606
Operating activities
Net income (loss)		(1,416)
Loss from discontinued operations, net of tax		409
Net income (loss) from continuing operations		(1,007)
Changes in operating assets and liabilities:
Unbilled receivables and retentions		2,718
Inventories		(511)
Income tax receivable		(416)
Other liabilities		(810)
Net cash provided by operating activities of continuing operations		(26)
Discontinued operations
Operating activities of discontinued operations		26
Net cash provided by (used in) discontinued operations		26
As Reported
Operating activities
Net income (loss)		(4,466)
Loss from discontinued operations, net of tax		1,079
Net income (loss) from continuing operations		(3,387)
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Depreciation and amortization		1,406
Impairment of long-lived assets		9
Provision for doubtful accounts		209
Gains on foreign currency transactions		(106)
Deferred income taxes		(597)
Stock-based compensation		1,326
Amortization of held-to-maturity investments		474
Changes in operating assets and liabilities:
Accounts receivable		43,819
Unbilled receivables and retentions		3,516
Inventories		(9,713)
Income tax receivable		(2,969)
Prepaid expenses and other assets		358
Accounts payable		(5,504)
Other liabilities		(3,496)
Net cash provided by operating activities of continuing operations		25,345
Investing activities
Acquisition of property and equipment		(2,705)
Redemptions of held-to-maturity investments		59,280
Purchases of held-to-maturity investments		(41,806)
Redemptions of available-for-sale investments		450
Net cash used in investing activities from continuing operations		15,219
Financing activities
Principal payments of capital lease obligations		(92)
Tax withholding payment related to net settlement of equity awards		(212)
Exercise of stock options		1,640
Net cash (used in) provided by financing activities from continuing operations		1,336
Discontinued operations
Operating activities of discontinued operations		(4,063)
Investing activities of discontinued operations		(268)
Net cash provided by (used in) discontinued operations		(4,331)
Net increase in cash and cash equivalents		37,569
Cash and cash equivalents at beginning of period		79,904
Cash and cash equivalents at end of period		117,473
Cash (refunds) paid, net during the period for:
Income taxes		1,803
Non-cash activities
Unrealized gain on investments, net of deferred tax expense of $4		2
Reclassification from share-based liability compensation to equity		384
Acquisitions of property and equipment included in accounts payable		$ 644
As Reported | ASU 2014-09
Discontinued operations
Cash and cash equivalents at beginning of period	$ 143,517