Impact of Adoption of New Accounting Standards - Statement Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 27, 2018	Oct. 28, 2017	Oct. 27, 2018	Oct. 28, 2017
Operating activities
Net income	$ 6,050	$ 7,517	$ 33,366	$ 1,635
Gain on sale of business, net of tax expense	391		(8,452)
Loss from discontinued operations, net of tax	599	33	2,449	1,521
Net income from continuing operations	7,040	7,550	27,363	3,156
Adjustments to reconcile net income to cash provided by operating activities
Depreciation and amortization			3,584	2,784
Loss from equity method investments	752		1,354
Impairment of long-lived assets				255
Provision for doubtful accounts			(27)	935
Impairment of intangible assets and goodwill				1,021
Gains on foreign currency transactions			(13)	(108)
Deferred income taxes			(614)	(1,094)
Stock-based compensation			2,517	2,535
Loss on disposition of property and equipment				15
Amortization of held-to-maturity investments			(459)	897
Changes in operating assets and liabilities:
Accounts receivable			22,261	39,861
Unbilled receivables and retentions			(28,782)	600
Inventories			(8,671)	(13,772)
Income tax receivable				(307)
Prepaid expenses and other assets			(831)	413
Accounts payable			(8,841)	(2,972)
Other liabilities			(6,184)	(4,225)
Net cash provided by operating activities of continuing operations			2,657	29,994
Investing activities
Acquisition of property and equipment			(4,135)	(5,455)
Proceeds from sale of business			31,994
Redemptions of held-to-maturity investments			153,029	105,758
Purchases of held-to-maturity investments			(169,402)	(88,763)
Redemptions of available-for-sale investments			2,250	450
Net cash used in investing activities from continuing operations			13,736	11,990
Financing activities
Principal payments of capital lease obligations			(111)	(173)
Tax withholding payment related to net settlement of equity awards			(975)	(313)
Exercise of stock options			71	2,164
Net cash (used in) provided by financing activities from continuing operations			(1,015)	1,678
Discontinued operations
Operating activities of discontinued operations			(7,188)	(5,875)
Investing activities of discontinued operations			(452)	(582)
Net cash used in discontinued operations			(7,640)	(6,457)
Net increase in cash and cash equivalents			7,738	37,205
Cash and cash equivalents at beginning of period			143,517	79,904
Cash and cash equivalents at end of period	$ 151,255	117,109	151,255	117,109
Cash (refunds) paid, net during the period for:
Income tax refund			5,270	1,803
Non-cash activities
Unrealized gain on investments, net of deferred tax expense of $4			57	29
Reclassification from share-based liability compensation to equity				384
Change in foreign currency translation adjustments			(31)
Acquisitions of property and equipment included in accounts payable			753	888
Effect of the Adoption of ASC Topic 606
Operating activities
Net income		705		(711)
Loss from discontinued operations, net of tax		362		771
Net income from continuing operations		1,067		60
Changes in operating assets and liabilities:
Unbilled receivables and retentions				(25)
Inventories				(151)
Income tax receivable				(307)
Other liabilities				123
Net cash provided by operating activities of continuing operations				(300)
Discontinued operations
Operating activities of discontinued operations				300
Net cash used in discontinued operations				300
As Reported
Operating activities
Net income		6,812		2,346
Loss from discontinued operations, net of tax		(329)		750
Net income from continuing operations		6,483		3,096
Adjustments to reconcile net income to cash provided by operating activities
Depreciation and amortization				2,784
Impairment of long-lived assets				255
Provision for doubtful accounts				935
Impairment of intangible assets and goodwill				1,021
Gains on foreign currency transactions				(108)
Deferred income taxes				(1,094)
Stock-based compensation				2,535
Loss on disposition of property and equipment				15
Amortization of held-to-maturity investments				897
Changes in operating assets and liabilities:
Accounts receivable				39,861
Unbilled receivables and retentions				625
Inventories				(13,621)
Prepaid expenses and other assets				413
Accounts payable				(2,972)
Other liabilities				(4,348)
Net cash provided by operating activities of continuing operations				30,294
Investing activities
Acquisition of property and equipment				(5,455)
Redemptions of held-to-maturity investments				105,758
Purchases of held-to-maturity investments				(88,763)
Redemptions of available-for-sale investments				450
Net cash used in investing activities from continuing operations				11,990
Financing activities
Principal payments of capital lease obligations				(173)
Tax withholding payment related to net settlement of equity awards				(313)
Exercise of stock options				2,164
Net cash (used in) provided by financing activities from continuing operations				1,678
Discontinued operations
Operating activities of discontinued operations				(6,175)
Investing activities of discontinued operations				(582)
Net cash used in discontinued operations				(6,757)
Net increase in cash and cash equivalents				37,205
Cash and cash equivalents at beginning of period				79,904
Cash and cash equivalents at end of period		$ 117,109		117,109
Cash (refunds) paid, net during the period for:
Income tax refund				1,803
Non-cash activities
Unrealized gain on investments, net of deferred tax expense of $4				29
Reclassification from share-based liability compensation to equity				384
Acquisitions of property and equipment included in accounts payable				$ 888
As Reported | ASU 2014-09
Discontinued operations
Cash and cash equivalents at beginning of period			$ 143,517