Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 26, 2015	Dec. 27, 2014
Cash flows from operating activities:
Net income (loss)	$ 44,035	$ 2,905	$ (31,118)
Reconciliation of net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	8,295	9,075	9,767
Stock-based compensation	7,666	6,248	6,752
Excess tax benefit from equity awards	1,036
Disposal of fixed assets	478	1,121	249
Inventory write-down	2,110	2,645	2,897
Deferred income taxes	(16,783)	345	17,915
Changes in fair value of contingent payments to Zygo Corporation	(1,175)	(56)	201
Changes in assets and liabilities:
Accounts receivable	(2,707)	(12,610)	3,861
Inventories	4,526	(16,431)	(7,173)
Inventories-delivered systems	399	(943)	4,988
Prepaid expenses and other	905	3,271	2,303
Accounts payable, accrued and other liabilities	2,462	4,167	1,790
Deferred revenue	(3,634)	1,006	(12,855)
Income taxes payable	(1,928)	828	(212)
Net cash provided by (used in) operating activities	45,685	1,571	(635)
Cash flows from investing activities:
Sales of marketable securities	5,955	3,383
Maturities of marketable securities	38,775	41,863	38,839
Purchases of marketable securities	(82,864)	(41,449)	(41,100)
Purchases of property, plant and equipment	(3,999)	(1,846)	(5,792)
Net cash provided by (used in) investing activities	(42,133)	1,951	(8,053)
Cash flows from financing activities:
Payments to Zygo Corporation related to acquisition	(315)	(851)	(587)
Proceeds from sale of shares under employee stock option plans and purchase plan	8,447	3,974	5,958
Excess tax benefit from equity awards	(1,036)
Taxes paid on net issuance of stock awards	(1,822)	(1,182)	(702)
Net cash provided by (used in) financing activities	5,274	220	(675)
Effect of exchange rate changes on cash and cash equivalents	82	(264)	(726)
Net increase (decrease) in cash and cash equivalents	8,908	3,478	(10,089)
Cash and cash equivalents, beginning of period	38,154	34,676	44,765
Cash and cash equivalents, end of period	47,062	38,154	34,676
Supplemental disclosure of cash flow information:
Cash paid (refund) for income taxes, net	3,767	(826)	861
Supplemental disclosure of non-cash investing activities:
Transfer of inventory to property, plant and equipment, net	$ 2,345	1,469	3,275
Share Repurchase Plans [Member]
Cash flows from financing activities:
Repurchases of common stock		$ (1,721)	$ (5,344)