Restructuring and Related Activities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restructuring Reserve [Roll Forward]
Restructuring and severance costs	$ 0	$ 481	$ 0	$ 1,950
MOSFETs Enhanced Competitiveness Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Current	1,660		1,660
Restructuring Reserve [Roll Forward]
Restructuring and severance costs		28		448	$ 3,204	$ 9,744	$ 5,367	$ 6,025	$ 2,328
Cash paid			(603)		(7,173)	(15,686)	(426)	(856)	(267)
Foreign currency translation						2	1
Balance at end of period	$ 1,660		1,660		2,263	6,232	12,172	7,230	$ 2,061
Balance at beginning of period			2,263	6,232	6,232	12,172	7,230	$ 2,061
Term of restructuring program	2 years
Global Cost Reduction Program [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve, Current	$ 2,922		2,922
Restructuring Reserve [Roll Forward]
Restructuring and severance costs		453		1,502	8,069	9,918	13,753
Cash paid			(2,573)		(7,168)	(16,237)	(986)
Foreign currency translation			(127)		500	(34)	(150)
Balance at end of period	$ 4,965		4,965		7,665	6,264	$ 12,617
Balance at beginning of period			$ 7,665	6,264	$ 6,264	$ 12,617
Global Cost Reduction Program [Member] | Diodes Segment [Member]
Restructuring Reserve [Roll Forward]
Restructuring and severance costs		13		13
Global Cost Reduction Program [Member] | Optoelectronic Components Segment [Member]
Restructuring Reserve [Roll Forward]
Restructuring and severance costs		242		242
Global Cost Reduction Program [Member] | Resistors And Inductors Segment [Member]
Restructuring Reserve [Roll Forward]
Restructuring and severance costs		84		935
Global Cost Reduction Program [Member] | Capacitors Segment [Member]
Restructuring Reserve [Roll Forward]
Restructuring and severance costs		85		246
Global Cost Reduction Program [Member] | Unallocated Amount to Segment [Member]
Restructuring Reserve [Roll Forward]
Restructuring and severance costs		$ 29		$ 66