Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 57,648	$ 30,202	$ 44,035
Reconciliation of net income to net cash provided by operating activities:
Depreciation and amortization	6,846	6,920	8,295
Stock-based compensation	11,382	8,819	7,666
Excess tax benefit from equity awards	1		1,036
(Gain) loss on disposal of fixed assets	(759)	631	478
Inventory write-down	3,012	2,020	2,110
Deferred income taxes	3,732	6,858	(16,783)
Changes in fair value of contingent payments to Zygo Corporation			(1,175)
Changes in assets and liabilities:
Accounts receivable	15,156	(19,523)	(2,707)
Inventories	(8,962)	(18,037)	4,526
Inventories-delivered systems	1,354	923	399
Prepaid expenses and other	(407)	(230)	905
Accounts payable, accrued and other liabilities	11,438	1,049	2,462
Deferred revenue	2,399	(915)	(3,634)
Income taxes payable	496	1,886	(1,928)
Net cash provided by operating activities	103,336	20,603	45,685
Cash flows from investing activities:
Payment for acquisition of certain assets	(2,000)	(2,000)
Payments to acquire 4D Technology, net of cash acquired	(37,163)
Sales of marketable securities	56,279	53,030	5,955
Maturities of marketable securities	38,700	77,250	38,775
Purchases of marketable securities	(53,523)	(129,766)	(82,864)
Purchases of property, plant and equipment	(7,486)	(5,204)	(3,999)
Proceeds from sale of property, plant and equipment	942
Net cash used in investing activities	(4,251)	(6,690)	(42,133)
Cash flows from financing activities:
Payments to Zygo Corporation related to acquisition			(315)
Proceeds from sale of shares under employee stock option plans and purchase plan	3,826	5,576	8,447
Excess tax benefit from equity awards			(1,036)
Taxes paid on net issuance of stock awards	(3,609)	(4,135)	(1,822)
Repurchases of common stock under share repurchase plans	(22,987)	(26,999)
Net cash provided by (used in) financing activities	(22,770)	(25,558)	5,274
Effect of exchange rate changes on cash and cash equivalents	(263)	(518)	82
Net increase (decrease) in cash and cash equivalents	76,052	(12,163)	8,908
Cash and cash equivalents, beginning of period	34,899	47,062	38,154
Cash and cash equivalents, end of period	110,951	34,899	47,062
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net	5,561	3,040	3,767
Supplemental disclosure of non-cash investing activities:
Transfers between inventory and property, plant and equipment, net	1,147	2,451	2,345
Unpaid property, plant and equipment at year end	$ 531	$ 957	$ 683