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 Other Comprehensive Income (Loss)	Treasury Stock	Noncontrolling Interest in Subsidiaries
Balance at beginning of period, shares at Dec. 31, 2019			286,877
Balance at beginning of period, shares at Dec. 31, 2019							(46,072)
Balance at beginning 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	64,497	63,889			63,889			608
Other comprehensive income (loss)	594	594				594
Treasury stock acquired through surrender of shares for tax withholding, shares							(5)
Treasury stock acquired through surrender of shares for tax withholding	(54)	(54)					$ (54)
Issuance of stock through share-based compensation plans, shares			216
Issuance of stock through share-based compensation plans	1,519	1,519		1,519
Share-based compensation	1,830	1,830		1,830
Balance at end of period, shares at Mar. 31, 2020			287,093
Balance at end of period, shares at Mar. 31, 2020							(46,077)
Balance at end of period at Mar. 31, 2020	$ 2,058,625	2,031,517	$ 287	1,931,088	297,966	19,709	$ (217,533)	27,108
Balance at beginning of period, shares at Dec. 31, 2020	288,923		288,923
Balance at beginning of period, shares at Dec. 31, 2020	(46,094)						(46,094)
Balance at beginning of period at Dec. 31, 2020	$ 2,353,959	2,325,699	$ 289	1,953,378	562,502	27,270	$ (217,740)	28,260
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	120,019	119,809			119,809			210
Other comprehensive income (loss)	(11,447)	(11,447)				(11,447)
Treasury stock acquired through surrender of shares for tax withholding, shares							(57)
Treasury stock acquired through surrender of shares for tax withholding	(1,321)	(1,321)					$ (1,321)
Issuance of stock through share-based compensation plans, shares			942
Issuance of stock through share-based compensation plans	8,561	8,561	$ 1	8,560
Share-based compensation	2,393	2,393		2,393
Cash dividends declared	(9,777)	(9,777)			(9,777)
Subsidiary dividends to noncontrolling interests	$ (150)							(150)
Balance at end of period, shares at Mar. 31, 2021	289,865		289,865
Balance at end of period, shares at Mar. 31, 2021	(46,151)						(46,151)
Balance at end of period at Mar. 31, 2021	$ 2,462,237	$ 2,433,917	$ 290	$ 1,964,331	$ 672,534	$ 15,823	$ (219,061)	$ 28,320