Note 1 - Summary of Significant Accounting Policies - Cumulative-effect Adjustments (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 29, 2018		Sep. 29, 2018	[2]	Jun. 30, 2018	[2]	Mar. 31, 2018	[2]	Dec. 30, 2017		Sep. 30, 2017	[2]	Jul. 01, 2017	[2]	Apr. 01, 2017	[2]	Dec. 29, 2018		Dec. 30, 2017		Dec. 31, 2016	Dec. 31, 2017
Deferred profit		$ 6,896								$ 6,608								$ 6,896		$ 6,608			$ 5,350
Income taxes payable		11,055								2,159								11,055		2,159			2,360
Retained earnings		111,670	[1]							150,726								111,670	[1]	150,726			151,783
Net sales		170,637	[2],[3]	$ 86,164	[3]	$ 99,817	[3]	$ 95,150	[3]	84,090	[2],[3]	$ 93,651		$ 93,866		$ 81,097		451,768	[2],[3]	352,704		$ 282,084
Income tax provision																		631		2,244		2,747
Net loss		$ (56,997)	[2],[3]	$ 4,803		$ 11,648		$ 8,122		$ 6,895	[2],[3]	$ 8,755		$ 10,430		$ 6,763		$ (32,424)		$ 32,843		$ 3,039
Basic: (in dollars per share)		$ (1.40)	[2],[4]	$ 0.17	[4]	$ 0.40	[4]	$ 0.28	[4]	$ 0.24	[2],[3],[4]	$ 0.31	[4]	$ 0.38	[4]	$ 0.25	[4]	$ (1.01)	[4]	$ 1.18	[4]	$ 0.11
Diluted: (in dollars per share)		$ (1.40)	[2],[3],[4]	$ 0.16	[4]	$ 0.39	[4]	$ 0.28	[4]	$ 0.23	[2],[3],[4]	$ 0.30	[4]	$ 0.36	[4]	$ 0.24	[4]	$ (1.01)	[4]	$ 1.14	[4]	$ 0.11
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Deferred profit		$ 11,125																$ 11,125
Retained earnings	[1]	108,181																108,181
Net sales																		448,797
Income tax provision																		92
Net loss																		$ (34,856)
Basic: (in dollars per share)																		$ (1.10)
Diluted: (in dollars per share)																		$ (1.10)
Accounting Standards Update 2014-09 [Member]
Deferred profit																							(1,258)
Income taxes payable																							201
Retained earnings																							$ 1,057
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Deferred profit		(4,229)																$ (4,229)
Retained earnings	[1]	$ 3,489																3,489
Net sales																		2,971
Income tax provision																		539
Net loss																		$ 2,432
Basic: (in dollars per share)																		$ 0.08
Diluted: (in dollars per share)																		$ 0.08

[1] Balance sheet line items include the cumulative-effect adjustment recorded on December 31, 2017.

[2] All quarters presented above were comprised of 13 weeks, except for the first quarter ended March 25, 2017, and the third quarter ended September 30, 2017, which were comprised of 12 and 14 weeks, respectively.

[3] We acquired Xcerra on October 1, 2018. The results of Xcerra have been included in our results of operations from the date of acquisition. See Note 2, "Business Acquisitions" for additional information regarding this transaction. Total operating expenses in the fourth quarter of 2018 include charges related to the acquisition of Xcerra as follows - $37.8 million in restructuring charges comprised of $19.1 million of inventory end-of-manufacturing write-downs related to one of Xcerra's products, employee severance costs of $17.8 million and $0.9 million for other restructuring costs. We also recorded $13.1 million for the amortization of acquisition-related intangibles.

[4] The sum of the four quarters may not agree to the year total due to rounding or losses within a quarter and the inclusion or exclusion of common stock equivalents.