Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 1,371,041	$ 1,354,023	$ 1,172,909	$ 1,152,616	$ 1,178,464	$ 1,083,917	$ 895,305	$ 894,964	$ 5,050,589	$ 4,052,650	$ 4,316,466
Gross Profit	278,501	241,085	192,320	188,908	222,984	182,240	123,454	120,761	900,814	649,439	710,565
Operating income	159,179	127,469	86,524	84,073	118,385	78,855	22,510	13,420	457,245	233,170	258,144
Income tax (benefit) expense	12,679	15,753	12,905	4,846	764	9,141	5,897	21,380	46,183	37,182	56,250
Net income (loss)	126,965	92,897	56,140	64,497	99,816	54,486	(9,006)	(22,668)	340,499	122,628	129,565
Net income (loss) attributable to Amkor	$ 126,674	$ 92,151	$ 55,424	$ 63,889	$ 99,147	$ 54,070	$ (9,450)	$ (22,879)	$ 338,138	$ 120,888	$ 127,092
Basic (in dollars per share)	$ 0.52	$ 0.38	$ 0.23	$ 0.27	$ 0.41	$ 0.23	$ (0.04)	$ (0.10)	$ 1.40	$ 0.50	$ 0.53
Diluted (in dollars per share)	$ 0.52	$ 0.38	$ 0.23	$ 0.26	$ 0.41	$ 0.23	$ (0.04)	$ (0.10)	$ 1.40	$ 0.50	$ 0.53
Condensed Income Statements, Captions [Line Items]
Change in valuation allowance	$ (20,200)				$ (3,800)			$ 14,900	$ (15,624)	$ 18,374	$ (12,662)
Loss on debt retirement									$ 3,042	$ 8,536	$ 1,512
6.375% Senior notes, due October 2022 | Senior notes
Condensed Income Statements, Captions [Line Items]
Loss on debt retirement							$ 8,400