Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended								12 Months Ended
	May 31, 2017	Nov. 30, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Net sales			$ 1,081,271	$ 1,144,192	$ 1,065,684	$ 1,025,319	$ 1,150,478	$ 1,148,884	$ 1,008,385	$ 899,284	$ 4,316,466	$ 4,207,031	$ 3,927,849
Gross Profit			182,370	200,707	169,717	157,771	224,341	223,888	176,616	136,234	710,565	761,079	709,891
Operating income			75,381	92,703	53,941	36,119	109,018	105,479	172,659	18,384	258,144	405,540	308,587
Income tax (benefit) expense			28,812	14,326	10,631	2,481	(13,613)	21,263	33,466	(1,325)	56,250	39,791	51,042
Net income (loss)			28,894	57,292	33,184	10,195	101,185	60,458	120,030	(13,968)	129,565	267,705	178,653
Net income (loss) attributable to Amkor			$ 28,295	$ 56,662	$ 32,591	$ 9,544	$ 100,059	$ 59,264	$ 119,013	$ (14,786)	$ 127,092	$ 263,550	$ 175,530
Basic (in dollars per share)			$ 0.12	$ 0.24	$ 0.14	$ 0.04	$ 0.42	$ 0.25	$ 0.50	$ (0.06)	$ 0.53	$ 1.10	$ 0.74
Diluted (in dollars per share)			$ 0.12	$ 0.24	$ 0.14	$ 0.04	$ 0.42	$ 0.25	$ 0.50	$ (0.06)	$ 0.53	$ 1.10	$ 0.74
Condensed Income Statements, Captions [Line Items]
Proceeds from sale of property, plant and equipment											$ 2,841	$ 141,530	$ 45,635
Gain on sale K1 factory											(5,310)	2,648	(1,390)
Net tax benefit from U.S. tax reform											$ (22,284)	$ 41,554	$ 0
Income tax expense from the Tax Act			$ 22,300
Korea
Condensed Income Statements, Captions [Line Items]
Proceeds from sale of property, plant and equipment	$ 142,400	$ 142,400
Gain on sale K1 factory	$ 108,100