Note 8 - Shareholders' Equity - Changes in Shareholders' Equity (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Balance				$ 927,556
Net income		$ 42,326	$ 48,638	78,354	$ 87,530
Other comprehensive income (loss)				(16,221)
Stock-based compensation				15,883
Withheld shares on restricted share units for withholding taxes				(7,042)
Stock options exercised				17,654
Issuance of common stock(a)	[1]			472,301
Cash dividends paid ($0.37 per share)				(18,458)
Non-controlling interest				(7)
Balance		1,470,020		1,470,020
Parent [Member]
Balance				927,419
Net income				78,354
Other comprehensive income (loss)				(16,221)
Stock-based compensation				15,883
Withheld shares on restricted share units for withholding taxes				(7,042)
Stock options exercised				17,654
Issuance of common stock(a)	[1]			472,301
Cash dividends paid ($0.37 per share)				(18,458)
Non-controlling interest
Balance		1,469,890		1,469,890
Noncontrolling Interest [Member]
Balance				137
Net income
Other comprehensive income (loss)
Stock-based compensation
Withheld shares on restricted share units for withholding taxes
Stock options exercised
Issuance of common stock(a)	[1]
Cash dividends paid ($0.37 per share)
Non-controlling interest				(7)
Balance		$ 130		$ 130

[1] The issuance of common stock (2,092,491 shares) during the six months ended June 30, 2018 relates to the acquisition of IXYS. See Note 2, Acquisitions for further discussion.