Note 3 - Acquisitions - Preliminary Price Allocation (Details) - USD ($) $ in Thousands					9 Months Ended
	Aug. 29, 2016	Apr. 04, 2016	Mar. 25, 2016	Oct. 01, 2015	Dec. 31, 2016	Jan. 02, 2016	Mar. 25, 2015	Dec. 27, 2014
Goodwill					$ 403,544	$ 189,767		$ 196,256
TVS Diode, Thyristor and IGBT Business [Member]
Cash	$ 104,000
Current assets, net	4,816
Goodwill	56,084
	104,000
Cash, net of acquired cash	104,000
Current assets, net	4,816
Payments to Acquire Businesses, Gross	104,000
TVS Diode, Thyristor and IGBT Business [Member] | Customer Relationships [Member]
Intangible assets, other than goodwill	31,800
TVS Diode, Thyristor and IGBT Business [Member] | Patented and Unpatented Technologies [Member]
Intangible assets, other than goodwill	8,800
TVS Diode, Thyristor and IGBT Business [Member] | Noncompete Agreements [Member]
Intangible assets, other than goodwill	$ 2,500
Menber's S.p.A. [Member]
Cash		$ 19,162
Current assets, net		12,919
Goodwill		8,091
		19,162
Cash, net of acquired cash		19,162
Property, plant, and equipment		1,693
Current liabilities		(7,220)
Other non-current liabilities		(1,444)
Total purchase consideration		19,200
Current assets, net		12,919
Payments to Acquire Businesses, Gross		19,162
Total purchase consideration		19,200
Other non-current liabilities		(1,444)
Menber's S.p.A. [Member] | Customer Relationships [Member]
Intangible assets, other than goodwill		3,050
Menber's S.p.A. [Member] | Patented and Unpatented Technologies [Member]
Intangible assets, other than goodwill		224
Menber's S.p.A. [Member] | Trademarks and Trade Names [Member]
Intangible assets, other than goodwill		$ 1,849
PolySwitch [Member]
Cash					344,500
Current assets, net			$ 60,228
Goodwill			165,088
			348,292
Cash, net of acquired cash					344,500
Property, plant, and equipment			51,613
Current liabilities			(35,280)
Other non-current liabilities			(5,020)
Original consideration			350,000
Post closing consideration adjustment received			(1,708)
Acquired cash			(3,810)
Acquired cash to be returned to seller			3,810
Total purchase consideration			348,292
Current assets, net			60,228
Land lease			4,290
Other long-term assets							$ 11,228
Payments to Acquire Businesses, Gross					$ 344,500
Estimated additional consideration payable			3,810
Total purchase consideration			348,292
Other non-current liabilities			(5,020)
PolySwitch [Member] | Customer Relationships [Member]
Intangible assets, other than goodwill			39,720
PolySwitch [Member] | Patented and Unpatented Technologies [Member]
Intangible assets, other than goodwill			$ 56,425
Sigmar [Member]
Cash				$ 5,558
Current assets, net				2,519
Goodwill				4,084
				6,459
Cash, net of acquired cash				5,558
Property, plant, and equipment				1,097
Current liabilities				(1,518)
Other non-current liabilities				(2,568)
Acquired cash to be returned to seller				901
Total purchase consideration				6,459
Current assets, net				2,519
Payments to Acquire Businesses, Gross				5,558
Estimated additional consideration payable				901
Total purchase consideration				6,459
Other non-current liabilities				(2,568)
Sigmar [Member] | Patents [Member]
Intangible assets, other than goodwill				$ 2,845