Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 25, 2016	Jun. 27, 2015
Cash flows from operating activities:
Net income	$ 9,498	$ 3,900
Reconciliation of net income to net cash provided by (used in) operating activities:
Depreciation and amortization	4,305	4,555
Stock-based compensation	3,432	2,982
Disposal of fixed assets	128	501
Inventory write-down	1,046	1,298
Deferred income taxes	(30)	136
Changes in fair value of contingent payments to Zygo Corporation	95	93
Changes in assets and liabilities:
Accounts receivable	(14,277)	(19,030)
Inventories	6,457	(8,442)
Inventories-delivered systems	(6,737)	339
Prepaid expenses and other	(151)	2,735
Accounts payable, accrued and other liabilities	(1,511)	4,283
Deferred revenue	12,080	(579)
Income taxes payable	(1,115)	72
Net cash provided by (used in) operating activities	13,220	(7,157)
Cash flows from investing activities:
Sales of marketable securities		2,383
Maturities of marketable securities	21,816	15,836
Purchases of marketable securities	(12,880)	(17,561)
Purchases of property, plant and equipment	(2,528)	(1,043)
Net cash provided by (used in) investing activities	6,408	(385)
Cash flows from financing activities:
Payments to Zygo Corporation related to acquisition	(315)	(417)
Proceeds from sale of shares under employee stock option plans and purchase plan	3,466	2,500
Taxes paid on net issuance of stock awards	(1,288)	(1,015)
Repurchases of common stock		(1,721)
Net cash provided by (used in) financing activities	1,863	(653)
Effect of exchange rate changes on cash and cash equivalents	387	(60)
Net increase (decrease) in cash and cash equivalents	21,878	(8,255)
Cash and cash equivalents, beginning of period	38,154	34,676
Cash and cash equivalents, end of period	60,032	26,421
Supplemental disclosure of non-cash investing activities:
Transfer of inventory to property, plant and equipment, net	212	$ 1,103
Transfer of property, plant and equipment to inventory, net	$ 491