Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Total Amkor Stockholders' Equity	Common Stock	Additional Paid- In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Noncontrolling Interest in Subsidiaries
Balance at beginning of period, shares at Dec. 31, 2017			285,129
Balance at beginning of period, shares at Dec. 31, 2017							(45,945)
Balance at beginning of period at Dec. 31, 2017	$ 1,719,709	$ 1,696,276	$ 285	$ 1,903,357	$ (13,903)	$ 22,519	$ (215,982)	$ 23,433
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	10,195
Net income attributable to Amkor	9,544	9,544			9,544
Net income attributable to noncontrolling interests	651							651
Other comprehensive income (loss)	15,052	15,052				15,052
Treasury stock acquired through surrender of shares for tax withholding, shares							(5)
Treasury stock acquired through surrender of shares for tax withholding	(56)	(56)					$ (56)
Issuance of stock through share-based compensation plans, shares			155
Issuance of stock through share-based compensation plans	1,022	1,022		1,022
Share-based compensation	1,287	1,287		1,287
Subsidiary dividends to noncontrolling interests	(135)							(135)
Balance at end of period, shares at Mar. 31, 2018			285,284
Balance at end of period, shares at Mar. 31, 2018							(45,950)
Balance at end of period at Mar. 31, 2018	$ 1,747,074	1,723,125	$ 285	1,905,666	(4,359)	37,571	$ (216,038)	23,949
Balance at beginning of period, shares at Dec. 31, 2018	285,352		285,352
Balance at beginning of period, shares at Dec. 31, 2018	(45,967)						(45,967)
Balance at beginning of period at Dec. 31, 2018	$ 1,855,900	1,830,540	$ 285	1,909,425	113,189	23,812	$ (216,171)	25,360
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(22,668)
Net income attributable to Amkor	(22,879)	(22,879)			(22,879)
Net income attributable to noncontrolling interests	211							211
Other comprehensive income (loss)	(2,356)	(2,356)				(2,356)
Treasury stock acquired through surrender of shares for tax withholding, shares							(5)
Treasury stock acquired through surrender of shares for tax withholding	(48)	(48)					$ (48)
Issuance of stock through share-based compensation plans, shares			78
Issuance of stock through share-based compensation plans	286	286		286
Share-based compensation	$ 1,468	1,468		1,468
Balance at end of period, shares at Mar. 31, 2019	285,430		285,430
Balance at end of period, shares at Mar. 31, 2019	(45,972)						(45,972)
Balance at end of period at Mar. 31, 2019	$ 1,832,582	$ 1,807,011	$ 285	$ 1,911,179	$ 90,310	$ 21,456	$ (216,219)	$ 25,571