Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	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
Dilutive Securities Adjustments [Line Items]
Net income available to Amkor common stockholders									$ 127,092	$ 263,550	$ 175,530
Weighted-average shares outstanding — basic									239,329	238,937	237,416
Effect of dilutive securities:
Weighted-average shares outstanding — diluted									239,741	239,651	238,034
Net income attributable to Amkor per common share:
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
Stock Options and Restricted Share Awards [Member]
Effect of dilutive securities:
Stock options and restricted share awards									412	714	618