Note 2 - Acquisitions and Dispositions (Details Textual) $ / shares in Units, $ in Thousands									12 Months Ended
	Jan. 17, 2018 USD ($) $ / shares	Jul. 07, 2017 USD ($)	Mar. 01, 2017 USD ($)	Feb. 28, 2017 USD ($)	Aug. 29, 2016 USD ($)	Apr. 04, 2016 USD ($)	Mar. 25, 2016 USD ($)	Oct. 01, 2015 USD ($)	Jan. 17, 2018 USD ($) $ / shares	Dec. 30, 2017 USD ($) $ / shares		Dec. 31, 2016 USD ($) $ / shares		Jan. 02, 2016 USD ($)	Dec. 31, 2015 USD ($)
Common Stock, Par or Stated Value Per Share | $ / shares										$ 0.01		$ 0.01
Finite-Lived Intangible Asset, Useful Life
Goodwill, Acquired During Period										$ 36,716	[1]	$ 232,934	[2]
Gain (Loss) on Disposition of Business												(1,391)
Marine Product Line [Member}
Gain (Loss) on Disposition of Business												1,400
Electronics [Member]
Goodwill, Acquired During Period							$ 103,800			36,716	[1]	162,172	[2]
Automotive [Member]
Goodwill, Acquired During Period							61,300				[1]	70,762	[2]
Trademarks and Trade Names [Member] | Minimum [Member]
Finite-Lived Intangible Asset, Useful Life										5 years
Trademarks and Trade Names [Member] | Maximum [Member]
Finite-Lived Intangible Asset, Useful Life										20 years
Monolith [Member]
Cost Method Investments												3,500			$ 3,500
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners															12.00%
U.S. Sensor [Member]
Payments to Acquire Businesses, Gross		$ 24,340
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables		1,500
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Inventory		$ 1,600
Monolith [Member]
Business Combination, Consideration Transferred				$ 15,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables				$ 700
Business Acquisition, Percentage of Voting Interests Acquired				62.00%
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low				$ 1,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High				10,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value			$ 3,500	$ 3,500
ON Portfolio [Member]
Payments to Acquire Businesses, Gross					$ 104,000
Business Combination, Consideration Transferred					104,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Inventory					700
Business Acquisition, Goodwill, Expected Tax Deductible Amount					$ 7,300
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual												21,800
ON Portfolio [Member] | Customer Relationships [Member]
Finite-Lived Intangible Asset, Useful Life					13 years 182 days
ON Portfolio [Member] | Patented and Unpatented Technologies [Member] | Minimum [Member]
Finite-Lived Intangible Asset, Useful Life					6 years
ON Portfolio [Member] | Patented and Unpatented Technologies [Member] | Maximum [Member]
Finite-Lived Intangible Asset, Useful Life					8 years 182 days
ON Portfolio [Member] | Noncompete Agreements [Member]
Finite-Lived Intangible Asset, Useful Life					4 years
Menber's S.p.A. [Member]
Business Combination, Consideration Transferred						$ 19,200
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Inventory						$ 200
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual												17,300
Menber's S.p.A. [Member] | Customer Relationships [Member]
Finite-Lived Intangible Asset, Useful Life						10 years
Menber's S.p.A. [Member] | Patented and Unpatented Technologies [Member]
Finite-Lived Intangible Asset, Useful Life						5 years
Menber's S.p.A. [Member] | Trademarks and Trade Names [Member]
Finite-Lived Intangible Asset, Useful Life						10 years
PolySwitch [Member]
Business Combination, Consideration Transferred							348,292
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Inventory							$ 6,900
Business Acquisition, Percentage of Voting Interests Acquired							100.00%
Business Acquisition, Goodwill, Expected Tax Deductible Amount							$ 64,900
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual												$ 126,500
PolySwitch [Member] | Customer Relationships [Member]
Finite-Lived Intangible Asset, Useful Life							15 years
PolySwitch [Member] | Patented and Unpatented Technologies [Member]
Finite-Lived Intangible Asset, Useful Life							10 years
Sigmar [Member]
Payments to Acquire Businesses, Gross								$ 5,558
Business Combination, Consideration Transferred								$ 6,459
Business Acquisition, Percentage of Voting Interests Acquired								100.00%
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High								$ 900
Subsequent Event [Member]
Share Price | $ / shares	$ 207.50								$ 207.50
Subsequent Event [Member] | IXYS Corporation [Member]
Business Acquisition, Share Price | $ / shares	$ 23								$ 23
Business Acquisition, Share Exchange Ratio	0.1265								0.1265
Business Combination, Consideration Transferred, Excluding Value of Stock Options Converted									$ 814,800
Payments to Acquire Businesses, Gross	$ 380,500
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	434,200
Business Combination, Value of Stock Options Converted to Company’s Stock Options	41,700
Business Combination, Consideration Transferred	$ 856,500
IXYS Corporation [Member] | Subsequent Event [Member]
Number of Customers	3,500
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.01								$ 0.01

[1] The 2017 additions resulted from the acquisitions of U.S. Sensor and Monolith.

[2] The 2016 additions resulted primarily from the acquisitions of PolySwitch, ON and Menber's.