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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to Amkor common stockholders	$ 55,424	$ (9,450)	$ 119,313	$ (32,329)
Weighted-average number of common shares outstanding - basic	241,098	239,508	241,009	239,461
Effect of dilutive securities:
Stock options and restricted share awards (in shares)	312	0	336	0
Weighted-average number of common shares outstanding - diluted	241,410	239,508	241,345	239,461
Net income (loss) attributable to Amkor per common share:
Basic (in dollars per share)	$ 0.23	$ (0.04)	$ 0.50	$ (0.14)
Diluted (in dollars per share)	$ 0.23	$ (0.04)	$ 0.49	$ (0.14)