Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 1,178,464	$ 1,083,917	$ 895,305	$ 894,964	$ 1,081,271	$ 1,144,192	$ 1,065,684	$ 1,025,319	$ 4,052,650	$ 4,316,466	$ 4,207,031
Gross Profit	222,984	182,240	123,454	120,761	182,370	200,707	169,717	157,771	649,439	710,565	761,079
Operating income	118,385	78,855	22,510	13,420	75,381	92,703	53,941	36,119	233,170	258,144	405,540
Income tax (benefit) expense	764	9,141	5,897	21,380	28,812	14,326	10,631	2,481	37,182	56,250	39,791
Net income (loss)	99,816	54,486	(9,006)	(22,668)	28,894	57,292	33,184	10,195	122,628	129,565	267,705
Net income (loss) attributable to Amkor	$ 99,147	$ 54,070	$ (9,450)	$ (22,879)	$ 28,295	$ 56,662	$ 32,591	$ 9,544	$ 120,888	$ 127,092	$ 263,550
Basic (in dollars per share)	$ 0.41	$ 0.23	$ (0.04)	$ (0.10)	$ 0.12	$ 0.24	$ 0.14	$ 0.04	$ 0.50	$ 0.53	$ 1.10
Diluted (in dollars per share)	$ 0.41	$ 0.23	$ (0.04)	$ (0.10)	$ 0.12	$ 0.24	$ 0.14	$ 0.04	$ 0.50	$ 0.53	$ 1.10
Condensed Income Statements, Captions [Line Items]
Change in valuation allowance	$ 3,800			$ (14,900)					$ (18,374)	$ 12,662	$ 6,763
Loss on debt retirement									8,536	1,512	4,835
Income tax expense related to impact of Tax Act					$ 22,300
Net tax benefit from U.S. tax reform					$ 41,600				$ 0	$ (22,284)	$ 41,554
6.375% Senior notes, due October 2022 | Senior notes
Condensed Income Statements, Captions [Line Items]
Loss on debt retirement			$ 8,400