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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net income attributable to Amkor common stockholders	$ 125,806	$ 55,424	$ 245,615	$ 119,313
Weighted-average number of common shares outstanding - basic	243,863	241,098	243,566	241,009
Effect of dilutive securities:
Share-based awards (in shares)	1,688	312	1,806	336
Weighted-average number of common shares outstanding - diluted	245,551	241,410	245,372	241,345
Net income attributable to Amkor per common share:
Basic (in dollars per share)	$ 0.52	$ 0.23	$ 1.01	$ 0.50
Diluted (in dollars per share)	$ 0.51	$ 0.23	$ 1.00	$ 0.49