CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balances (in shares) at Dec. 26, 2015		58,088,969
Balances at Dec. 26, 2015	$ 294,681	$ 58	$ 718,904	$ (2,222)	$ (422,059)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to exercise of options for cash (in shares)		232,190
Issuance of common stock pursuant to exercise of options for cash	2,003		2,003
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		1,579,218
Issuance of common stock pursuant to vesting of restricted stock units	2	$ 2
Issuance of common stock under the Employee Stock Purchase Plan (in shares)		557,281
Issuance of common stock under the Employee Stock Purchase Plan	3,741	$ 1	3,740
Issuance of common stock pursuant to Cascade Microtech acquisition (in shares)		10,450,189
Issuance of common stock pursuant to Cascade Microtech acquisition	97,079	$ 10	97,069
Stock-based compensation	11,625		11,625
Other comprehensive income	(1,518)			(1,518)
Net income (loss)	(6,557)				(6,557)
Balances (in shares) at Dec. 31, 2016		70,907,847
Balances at Dec. 31, 2016	401,056	$ 71	833,341	(3,740)	(428,616)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to exercise of options for cash (in shares)		1,473,389
Issuance of common stock pursuant to exercise of options for cash	13,837	$ 1	13,836
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		1,364,612
Issuance of common stock pursuant to vesting of restricted stock units	1	$ 1
Issuance of common stock under the Employee Stock Purchase Plan (in shares)		655,961
Issuance of common stock under the Employee Stock Purchase Plan	5,695	$ 1	5,694
Issuance of common stock pursuant to Cascade Microtech acquisition	0
Common stock withheld from vesting of restricted stock units for tax (in shares)		(502,016)
Common stock withheld from vesting of restricted stock units for tax	(6,886)		(6,886)
Purchase and retirement of common stock (in shares)		(1,367,617)
Purchase and retirement of common stock	(18,970)	$ (1)	(18,969)
Stock-based compensation	16,230		16,230
ASU 2017-12 Adoption	0		(130)		130
Other comprehensive income	6,761			6,761
Net income (loss)	$ 40,913				40,913
Balances (in shares) at Dec. 30, 2017	72,532,176	72,532,176
Balances at Dec. 30, 2017	$ 458,637	$ 73	843,116	3,021	(387,573)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to exercise of options for cash (in shares)		134,609
Issuance of common stock pursuant to exercise of options for cash	1,158		1,158
Issuance of common stock pursuant to vesting of restricted stock units (in shares)		1,287,107
Issuance of common stock pursuant to vesting of restricted stock units	1	$ 1
Issuance of common stock under the Employee Stock Purchase Plan (in shares)		610,297
Issuance of common stock under the Employee Stock Purchase Plan	6,662	$ 1	6,661
Issuance of common stock pursuant to Cascade Microtech acquisition	0
Common stock withheld from vesting of restricted stock units for tax (in shares)		(424,477)
Common stock withheld from vesting of restricted stock units for tax	(5,792)	$ (1)	(5,791)
Stock-based compensation	17,753		17,753
ASU 2017-12 Adoption	(50)				(50)
Other comprehensive income	(2,241)			(2,241)
Net income (loss)	$ 104,036				104,036
Balances (in shares) at Dec. 29, 2018	74,139,712
Balances at Dec. 29, 2018	$ 580,164	$ 74	$ 862,897	$ 780	$ (283,587)