Segment Information (Details) $ in Thousands	3 Months Ended					6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jul. 01, 2017 USD ($)	Apr. 01, 2017 USD ($)	Jun. 30, 2018 USD ($) Segment	Jul. 01, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment						5
Product Sales	$ 760,996			$ 643,128		$ 1,477,752	$ 1,247,923
Royalty Revenues	34			36		73	42
Total Revenue	761,030	$ 673,462	$ 677,941	643,164	$ 604,801	1,477,825	1,247,965	$ 2,599,368	$ 2,317,328
Gross Margin	227,238	177,376	190,147	173,837	161,749	432,538	335,586	703,109	573,822
Segment Operating Income	193,740			144,129		365,918	274,639
Restructuring and severance Costs	0			(481)		0	(1,950)
Operating income	123,293	76,006	95,416	85,005	67,578	227,355	152,583	324,005	197,058
Unallocated Other Income (Expense)	(25,734)	(8,981)	(9,228)	(9,296)	(17,136)	(37,777)	(26,432)	(44,641)	(102,842)
Income before taxes	97,559	$ 67,025	$ 86,188	75,709	$ 50,442	189,578	126,151	279,364	94,216
Distributors [Member]
Segment Reporting Information [Line Items]
Total Revenue	446,016			372,802		850,076	718,505	1,484,276	1,280,060
OEMs [Member]
Segment Reporting Information [Line Items]
Total Revenue	262,779			223,367		526,829	438,014	931,291	861,322
EMS companies [Member]
Segment Reporting Information [Line Items]
Total Revenue	52,235			46,995		100,920	91,446	183,801	175,946
Industrial [Member]
Segment Reporting Information [Line Items]
Total Revenue	295,617			232,874		575,829	449,640	934,631	796,031
Automotive [Member]
Segment Reporting Information [Line Items]
Total Revenue	209,858			175,884		418,252	351,227	727,220	640,767
Telecommunications [Member]
Segment Reporting Information [Line Items]
Total Revenue	46,467			47,283		92,391	93,118	190,682	193,456
Computing [Member]
Segment Reporting Information [Line Items]
Total Revenue	53,657			47,498		101,088	88,568	198,850	172,481
Consumer Products [Member]
Segment Reporting Information [Line Items]
Total Revenue	40,939			38,949		78,198	68,556	145,243	150,741
Power Supplies [Member]
Segment Reporting Information [Line Items]
Total Revenue	41,326			41,038		75,569	75,896	160,038	132,555
Military and Aerospace [Member]
Segment Reporting Information [Line Items]
Total Revenue	40,260			32,548		75,474	65,724	132,898	128,523
Medical [Member]
Segment Reporting Information [Line Items]
Total Revenue	32,906			27,090		61,024	55,236	109,806	102,774
Asia [Member]
Segment Reporting Information [Line Items]
Total Revenue	302,868			272,513		588,346	529,571	1,091,107	948,195
Americas [Member]
Segment Reporting Information [Line Items]
Total Revenue	185,561			149,501		349,496	291,219	605,904	558,590
Europe [Member]
Segment Reporting Information [Line Items]
Total Revenue	272,601			221,150		539,983	427,175	$ 902,357	$ 810,543
MOSFETS Segment [Member]
Segment Reporting Information [Line Items]
Product Sales	136,559			114,035		264,053	218,877
Royalty Revenues	0			0		12	0
Total Revenue	136,559			114,035		264,065	218,877
Gross Margin	38,427			25,357		70,449	46,074
Segment Operating Income	28,517			16,680		51,075	28,483
Diodes Segment [Member]
Segment Reporting Information [Line Items]
Product Sales	182,466			155,345		349,483	299,930
Royalty Revenues	0			0		0	0
Total Revenue	182,466			155,345		349,483	299,930
Gross Margin	52,408			41,762		95,608	79,924
Segment Operating Income	47,100			36,878		85,031	70,320
Optoelectronic Components Segment [Member]
Segment Reporting Information [Line Items]
Product Sales	75,709			72,633		147,667	137,895
Royalty Revenues	0			0		0	0
Total Revenue	75,709			72,633		147,667	137,895
Gross Margin	26,404			25,607		53,637	48,049
Segment Operating Income	22,165			21,676		44,959	38,793
Resistors And Inductors Segment [Member]
Segment Reporting Information [Line Items]
Product Sales	253,913			208,949		497,932	409,195
Royalty Revenues	34			36		61	42
Total Revenue	253,947			208,985		497,993	409,237
Gross Margin	84,969			62,135		163,499	123,350
Segment Operating Income	76,248			54,749		146,250	108,707
Capacitors Segment [Member]
Segment Reporting Information [Line Items]
Product Sales	112,349			92,166		218,617	182,026
Royalty Revenues	0			0		0	0
Total Revenue	112,349			92,166		218,617	182,026
Gross Margin	25,030			18,976		49,345	38,189
Segment Operating Income	19,710			14,146		38,603	28,336
Unallocated Amount to Segment [Member]
Segment Reporting Information [Line Items]
Segment Operating Income	(70,447)			(58,643)		(138,563)	(120,106)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment Operating Income	193,740			144,129		365,918	274,639
Unallocated Amount to Segment [Member]
Segment Reporting Information [Line Items]
Restructuring and severance Costs	0			(481)		0	(1,950)
Unallocated Other Income (Expense)	$ (25,734)			$ (9,296)		$ (37,777)	$ (26,432)