Earnings Per Share - Computation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income (loss) attributable to Amkor common stockholders	$ (9,450)	$ 32,591	$ (32,329)	$ 42,135
Weighted-average number of common shares outstanding — basic	239,508	239,351	239,461	239,283
Effect of dilutive securities:
Stock options and restricted share awards (in shares)	0	453	0	522
Weighted-average number of common shares outstanding — diluted	239,508	239,804	239,461	239,805
Net income (loss) attributable to Amkor per common share:
Basic (in dollars per share)	$ (0.04)	$ 0.14	$ (0.14)	$ 0.18
Diluted (in dollars per share)	$ (0.04)	$ 0.14	$ (0.14)	$ 0.18