Consolidated Statements of Stockholders' Equity - 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	129,565	127,092			127,092			2,473
Total other comprehensive income (loss)	1,293	1,293				1,293
Treasury stock acquired through surrender of shares for tax withholding, shares							(22)
Treasury stock acquired through surrender of shares for tax withholding	(189)	(189)					$ (189)
Issuance of stock through share-based compensation plans, shares			223
Issuance of stock through share-based compensation plans	1,050	1,050		1,050
Share-based compensation	5,018	5,018		5,018
Subsidiary dividends to noncontrolling interests	(546)							(546)
Balance at end of period, shares at Dec. 31, 2018			285,352
Balance at end of period, shares at Dec. 31, 2018							(45,967)
Balance at end 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	122,628	120,888			120,888			1,740
Total other comprehensive income (loss)	(4,697)	(4,697)				(4,697)
Treasury stock acquired through surrender of shares for tax withholding, shares							(105)
Treasury stock acquired through surrender of shares for tax withholding	(1,308)	(1,308)					$ (1,308)
Issuance of stock through share-based compensation plans, shares			1,525
Issuance of stock through share-based compensation plans	11,405	11,405	$ 2	11,403
Share-based compensation	6,911	6,911		6,911
Subsidiary dividends to noncontrolling interests	$ (600)							(600)
Balance at end of period, shares at Dec. 31, 2019	286,877		286,877
Balance at end of period, shares at Dec. 31, 2019	(46,072)						(46,072)
Balance at end of period at Dec. 31, 2019	$ 1,990,239	1,963,739	$ 287	1,927,739	234,077	19,115	$ (217,479)	26,500
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	340,499	338,138			338,138			2,361
Total other comprehensive income (loss)	8,155	8,155				8,155
Treasury stock acquired through surrender of shares for tax withholding, shares							(22)
Treasury stock acquired through surrender of shares for tax withholding	(261)	(261)					$ (261)
Issuance of stock through share-based compensation plans, shares			2,046
Issuance of stock through share-based compensation plans	17,611	17,611	$ 2	17,609
Share-based compensation	8,030	8,030		8,030
Dividends, Cash	(9,713)	(9,713)			(9,713)
Subsidiary dividends to noncontrolling interests	$ (601)							(601)
Balance at end of period, shares at Dec. 31, 2020	288,923		288,923
Balance at end of period, shares at Dec. 31, 2020	(46,094)						(46,094)
Balance at end of period at Dec. 31, 2020	$ 2,353,959	$ 2,325,699	$ 289	$ 1,953,378	$ 562,502	$ 27,270	$ (217,740)	$ 28,260