Earnings Per Share - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income (loss) attributable to Amkor common stockholders	$ (22,879)	$ 9,544
Weighted-average number of common shares outstanding — basic	239,414	239,214
Effect of dilutive securities:
Stock options and restricted share awards (in shares)	0	602
Weighted-average number of common shares outstanding — diluted	239,414	239,816
Net income (loss) attributable to Amkor per common share:
Basic (in dollars per share)	$ (0.10)	$ 0.04
Diluted (in dollars per share)	$ (0.10)	$ 0.04