CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Cash flows from operating activities:
Net Income (loss)	$ 40,913	$ (6,557)	$ (1,523)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation	13,626	11,371	10,634
Amortization	30,940	35,427	13,137
Impairment of long-lived assets	0	12,400	8
Amortization (accretion) of discount on investments	38	(31)	(10)
Stock-based compensation expense	16,339	11,686	12,075
Amortization of debt issuance costs	619	307	0
Deferred income tax benefit	(590)	(45,022)	(14)
Provision (benefit) for doubtful accounts receivable	(99)	15	18
Provision for excess and obsolete inventories	9,259	6,631	6,493
Acquired inventory step-up amortization	569	10,022	0
Loss (gain) on disposal off of long-lived assets	510	361	(1,009)
Non-cash restructuring	114	964	500
Foreign currency transaction gains	(1,717)	(77)	(275)
Gain on derivative instruments	(10)	(51)	0
Changes in assets and liabilities:
Accounts receivable	(10,651)	(6,847)	8,261
Inventories	(15,635)	(11,733)	(8,167)
Prepaid expenses and other current assets	870	(3,292)	173
Refundable income taxes	(413)	126	782
Other assets	61	(248)	250
Accounts payable	741	3,433	(2,036)
Accrued liabilities	810	786	(333)
Income taxes payable	62	(1,127)	19
Deferred rent and other liabilities	111	126	52
Deferred revenues	(30)	(283)	(2,413)
Net cash provided by operating activities	86,323	17,423	36,122
Cash flows from investing activities:
Acquisition of property, plant and equipment	(17,756)	(11,521)	(8,640)
Acquisition of Cascade Microtech, net of cash acquired	0	(228,031)	0
Proceeds from sale of subsidiary	68	47	53
Proceeds from sale of property and property, plant and equipment	0	53	1,200
Purchases of marketable securities	(50,733)	(10,587)	(66,234)
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities	8,996	44,500	74,750
Change in restricted cash	(248)	(779)	0
Net cash provided by (used in) investing activities	(59,673)	(206,318)	1,129
Cash flows from financing activities:
Proceeds from issuances of common stock	19,510	5,745	3,418
Purchase and retirement of common stock	(18,970)	0	(8,210)
Tax withholdings related to net share settlements of equity awards	(6,885)	0	0
Proceeds from term loan debt	0	150,000	0
Payments on term loan debt	(33,125)	(10,625)	0
Payment of term loan debt issuance costs	0	(1,506)	0
Net cash provided by (used in) financing activities	(39,470)	143,614	(4,792)
Effect of exchange rate changes on cash and cash equivalents	2,596	425	(135)
Net increase (decrease) in cash and cash equivalents	(10,224)	(44,856)	32,324
Cash and cash equivalents, beginning of year	101,408	146,264	113,940
Cash and cash equivalents, end of year	91,184	101,408	146,264
Non-cash investing and financing activities:
Fair value of stock issued in connection with the acquisition of Cascade Microtech	0	97,080	0
Fair value of stock options and restricted stock-based awards assumed in connection with the acquisition of Cascade Microtech	0	7,776	0
Fair value of vested stock options and restricted stock-based awards paid in cash in connection with the acquisition of Cascade Microtech	0	12,815	0
Change in accounts payable and accrued liabilities related to property, plant and equipment purchases	(33)	(732)	361
Supplemental disclosure of cash flow information:
Income taxes paid, net	3,172	2,567	27
Cash paid for interest	$ 3,836	$ 2,110	$ 0