Segment Information (Details) $ in Thousands	3 Months Ended					9 Months Ended		12 Months Ended
	Sep. 29, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jul. 01, 2017 USD ($)	Apr. 01, 2017 USD ($)	Sep. 29, 2018 USD ($) Segment	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment						5
Product Sales	$ 780,939		$ 677,933			$ 2,258,691	$ 1,925,856
Royalty Revenues	33		8			106	50
Total Revenue	780,972	$ 673,462	677,941	$ 643,164	$ 604,801	2,258,797	1,925,906	$ 2,599,368	$ 2,317,328
Gross Margin	236,296	177,376	190,147	173,837	161,749	668,834	525,733	703,109	573,822
Segment Operating Income	203,904		160,375			569,822	435,014
Restructuring and severance Costs	0		(3,244)			0	(5,194)
Operating income	138,098	76,006	95,416	85,005	67,578	365,453	247,999	324,005	197,058
Unallocated Other Income (Expense)	(11,290)	(8,981)	(9,228)	(9,296)	(17,136)	(49,067)	(35,660)	(44,641)	(102,842)
Income before taxes	126,808	$ 67,025	86,188	$ 75,709	$ 50,442	316,386	212,339	279,364	94,216
Distributors [Member]
Segment Reporting Information [Line Items]
Total Revenue	452,051		383,727			1,302,127	1,102,232	1,484,276	1,280,060
OEMs [Member]
Segment Reporting Information [Line Items]
Total Revenue	276,299		247,551			803,128	685,565	931,291	861,322
EMS companies [Member]
Segment Reporting Information [Line Items]
Total Revenue	52,622		46,663			153,542	138,109	183,801	175,946
Industrial [Member]
Segment Reporting Information [Line Items]
Total Revenue	283,134		242,038			858,963	691,678	934,631	796,031
Automotive [Member]
Segment Reporting Information [Line Items]
Total Revenue	224,041		185,781			642,293	537,008	727,220	640,767
Telecommunications [Member]
Segment Reporting Information [Line Items]
Total Revenue	51,935		50,710			144,326	143,828	190,682	193,456
Computing [Member]
Segment Reporting Information [Line Items]
Total Revenue	62,774		55,380			163,862	143,948	198,850	172,481
Consumer Products [Member]
Segment Reporting Information [Line Items]
Total Revenue	48,583		40,155			126,781	108,711	145,243	150,741
Power Supplies [Member]
Segment Reporting Information [Line Items]
Total Revenue	34,899		44,327			110,468	120,223	160,038	132,555
Military and Aerospace [Member]
Segment Reporting Information [Line Items]
Total Revenue	41,881		33,029			117,355	98,753	132,898	128,523
Medical [Member]
Segment Reporting Information [Line Items]
Total Revenue	33,725		26,521			94,749	81,757	109,806	102,774
Asia [Member]
Segment Reporting Information [Line Items]
Total Revenue	315,701		282,416			904,047	811,987	1,091,107	948,195
Americas [Member]
Segment Reporting Information [Line Items]
Total Revenue	195,753		157,651			545,249	448,870	605,904	558,590
Europe [Member]
Segment Reporting Information [Line Items]
Total Revenue	269,518		237,874			809,501	665,049	$ 902,357	$ 810,543
MOSFETS Segment [Member]
Segment Reporting Information [Line Items]
Product Sales	144,227		126,522			408,280	345,399
Royalty Revenues	33		0			45	0
Total Revenue	144,260		126,522			408,325	345,399
Gross Margin	38,991		32,349			109,440	78,423
Segment Operating Income	29,502		23,434			80,577	51,917
Diodes Segment [Member]
Segment Reporting Information [Line Items]
Product Sales	186,492		160,562			535,975	460,492
Royalty Revenues	0		0			0	0
Total Revenue	186,492		160,562			535,975	460,492
Gross Margin	54,690		43,575			150,298	123,499
Segment Operating Income	49,561		38,694			134,592	109,014
Optoelectronic Components Segment [Member]
Segment Reporting Information [Line Items]
Product Sales	76,443		77,145			224,110	215,040
Royalty Revenues	0		0			0	0
Total Revenue	76,443		77,145			224,110	215,040
Gross Margin	27,653		29,042			81,290	77,091
Segment Operating Income	23,144		25,214			68,103	64,007
Resistors And Inductors Segment [Member]
Segment Reporting Information [Line Items]
Product Sales	257,330		217,489			755,262	626,684
Royalty Revenues	0		8			61	50
Total Revenue	257,330		217,497			755,323	626,734
Gross Margin	88,213		65,586			251,712	188,936
Segment Operating Income	80,042		58,328			226,292	167,035
Capacitors Segment [Member]
Segment Reporting Information [Line Items]
Product Sales	116,447		96,215			335,064	278,241
Royalty Revenues	0		0			0	0
Total Revenue	116,447		96,215			335,064	278,241
Gross Margin	26,749		19,595			76,094	57,784
Segment Operating Income	21,655		14,705			60,258	43,041
Unallocated Amount to Segment [Member]
Segment Reporting Information [Line Items]
Segment Operating Income	(65,806)		(61,715)			(204,369)	(181,821)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment Operating Income	203,904		160,375			569,822	435,014
Unallocated Amount to Segment [Member]
Segment Reporting Information [Line Items]
Restructuring and severance Costs	0		(3,244)			0	(5,194)
Unallocated Other Income (Expense)	$ (11,290)		$ (9,228)			$ (49,067)	$ (35,660)