Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Cash flows from operating activities:
Net income	$ 30,202	$ 44,035	$ 2,905
Reconciliation of net income to net cash provided by operating activities:
Depreciation and amortization	6,920	8,295	9,075
Stock-based compensation	8,819	7,666	6,248
Excess tax benefit from equity awards		1,036
Disposal of fixed assets	631	478	1,121
Inventory write-down	2,020	2,110	2,645
Deferred income taxes	6,858	(16,783)	345
Changes in fair value of contingent payments to Zygo Corporation		(1,175)	(56)
Changes in assets and liabilities:
Accounts receivable	(19,523)	(2,707)	(12,610)
Inventories	(18,037)	4,526	(16,431)
Inventories-delivered systems	923	399	(943)
Prepaid expenses and other	(230)	905	3,271
Accounts payable, accrued and other liabilities	1,049	2,462	4,167
Deferred revenue	(915)	(3,634)	1,006
Income taxes payable	1,886	(1,928)	828
Net cash provided by operating activities	20,603	45,685	1,571
Cash flows from investing activities:
Payment for acquisition of certain assets	(2,000)
Sales of marketable securities	53,030	5,955	3,383
Maturities of marketable securities	77,250	38,775	41,863
Purchases of marketable securities	(129,766)	(82,864)	(41,449)
Purchases of property, plant and equipment	(5,204)	(3,999)	(1,846)
Net cash (used in) provided by investing activities	(6,690)	(42,133)	1,951
Cash flows from financing activities:
Payments to Zygo Corporation related to acquisition		(315)	(851)
Proceeds from sale of shares under employee stock option plans and purchase plan	5,576	8,447	3,974
Excess tax benefit from equity awards		(1,036)
Taxes paid on net issuance of stock awards	(4,135)	(1,822)	(1,182)
Net cash (used in) provided by financing activities	(25,558)	5,274	220
Effect of exchange rate changes on cash and cash equivalents	(518)	82	(264)
Net (decrease) increase in cash and cash equivalents	(12,163)	8,908	3,478
Cash and cash equivalents, beginning of period	47,062	38,154	34,676
Cash and cash equivalents, end of period	34,899	47,062	38,154
Supplemental disclosure of cash flow information:
Cash paid (refund) for income taxes, net	3,040	3,767	(826)
Supplemental disclosure of non-cash investing activities:
Transfer of inventory to property, plant and equipment, net	2,451	2,345	1,469
Property, plant and equipment included in accounts payable	957	$ 683	36
Share Repurchase Plans [Member]
Cash flows from financing activities:
Repurchases of common stock	$ (26,999)		$ (1,721)