Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 45,624	$ 19,404
Reconciliation of net income to net cash provided by operating activities:
Depreciation and amortization	4,962	5,219
Stock-based compensation	8,229	6,775
Disposal of fixed assets	38	98
Inventory write-down	870	1,412
Deferred income taxes	4,668	2,153
Changes in assets and liabilities:
Accounts receivable	11,520	1,418
Inventories	(6,351)	(16,828)
Inventories-delivered systems	(324)	(864)
Prepaid expenses and other	(1,224)	(3,850)
Accounts payable, accrued and other liabilities	9,623	709
Deferred revenue	5,126	(1,204)
Income taxes payable	647	942
Net cash provided by operating activities	83,408	15,384
Cash flows from investing activities:
Payments to acquire certain assets	(2,000)	(2,000)
Sales of marketable securities	19,776	28,624
Maturities of marketable securities	32,195	62,923
Purchases of marketable securities	(46,604)	(104,984)
Purchases of property, plant and equipment	(2,942)	(2,342)
Net cash provided by (used in) investing activities	425	(17,779)
Cash flows from financing activities:
Proceeds from sale of shares under employee stock option plans and purchase plan	3,826	3,678
Taxes paid on net issuance of stock awards	(3,122)	(3,838)
Repurchases of common stock under share repurchase plans	(22,987)
Net cash used in financing activities	(22,283)	(160)
Effect of exchange rate changes on cash and cash equivalents	(346)	(466)
Net increase (decrease) in cash and cash equivalents	61,204	(3,021)
Cash and cash equivalents, beginning of period	34,899	47,062
Cash and cash equivalents, end of period	96,103	44,041
Supplemental disclosure of non-cash investing activities:
Transfer of property, plant and equipment to inventory	893	$ 205
Transfer of inventory to property, plant and equipment	291
Property, plant and equipment included in accounts payable, accrued and other liabilities	$ 1,684