Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net income	$ 6,903	$ 34,056
Reconciliation of net income to net cash from operating activities:
Depreciation and amortization	5,061	3,326
Stock-based compensation	6,314	5,017
Disposal of fixed assets	(861)	51
Inventory write-down	2,922	269
Deferred income taxes		4,320
Changes in assets and liabilities:
Accounts receivable	473	7,193
Inventories	(8,290)	(1,722)
Inventories-delivered systems	(830)	(322)
Prepaid expenses and other	(1,974)	(3,422)
Operating lease - right of use assets	1,077
Accounts payable, accrued and other liabilities	(10,941)	7,204
Deferred revenue	738	2,464
Operating lease liabilities	(888)
Income taxes payable	(2,007)	537
Net cash provided by (used in) operating activities	(2,303)	58,971
Cash flows from investing activities:
Payments to acquire certain assets		(2,000)
Sales of marketable securities	1,627	18,507
Maturities of marketable securities	24,700	17,345
Purchases of marketable securities	(36,093)	(16,320)
Purchases of property, plant and equipment	(8,314)	(1,761)
Proceeds from sale of property, plant and equipment	896
Net cash provided by (used in) investing activities	(17,184)	15,771
Cash flows from financing activities:
Proceeds from sale of shares under employee stock option plans and purchase plan	4,535	2,709
Taxes paid on net issuance of stock awards	(2,328)	(2,731)
Repurchases of common stock under share repurchase plans		(22,987)
Net cash provided by (used in) financing activities	2,207	(23,009)
Effect of exchange rate changes on cash and cash equivalents	364	(431)
Net increase (decrease) in cash and cash equivalents	(16,916)	51,302
Cash and cash equivalents, beginning of period	110,951	34,899
Cash and cash equivalents, end of period	94,035	86,201
Supplemental disclosure of non-cash investing activities:
Transfers between inventory and property, plant and equipment, net	755	73
Unpaid property, plant and equipment	$ 662	$ 555