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	120,637	119,313			119,313			1,324
Other comprehensive income (loss)	157	157				157
Treasury stock acquired through surrender of shares for tax withholding, shares							(11)
Treasury stock acquired through surrender of shares for tax withholding	(113)	(113)					$ (113)
Issuance of stock through share-based compensation plans, shares			442
Issuance of stock through share-based compensation plans	2,741	2,741		2,741
Share-based compensation	3,567	3,567		3,567
Subsidiary dividends to non-controlling interests	(300)							(300)
Balance at end of period, shares at Jun. 30, 2020			287,319
Balance at end of period, shares at Jun. 30, 2020							(46,083)
Balance at end of period at Jun. 30, 2020	2,116,928	2,089,404	$ 287	1,934,047	353,390	19,272	$ (217,592)	27,524
Balance at beginning of period, shares at Mar. 31, 2020			287,093
Balance at beginning of period, shares at Mar. 31, 2020							(46,077)
Balance at beginning of period at Mar. 31, 2020	2,058,625	2,031,517	$ 287	1,931,088	297,966	19,709	$ (217,533)	27,108
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	56,140	55,424			55,424			716
Other comprehensive income (loss)	(437)	(437)				(437)
Treasury stock acquired through surrender of shares for tax withholding, shares							(6)
Treasury stock acquired through surrender of shares for tax withholding	(59)	(59)					$ (59)
Issuance of stock through share-based compensation plans, shares			226
Issuance of stock through share-based compensation plans	1,222	1,222		1,222
Share-based compensation	1,737	1,737		1,737
Subsidiary dividends to non-controlling interests	(300)							(300)
Balance at end of period, shares at Jun. 30, 2020			287,319
Balance at end of period, shares at Jun. 30, 2020							(46,083)
Balance at end of period at Jun. 30, 2020	$ 2,116,928	2,089,404	$ 287	1,934,047	353,390	19,272	$ (217,592)	27,524
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	246,477	245,615			245,615			862
Other comprehensive income (loss)	(11,157)	(11,157)				(11,157)
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			1,192
Issuance of stock through share-based compensation plans	10,024	10,024	$ 1	10,023
Share-based compensation	4,938	4,938		4,938
Cash dividends declared	(19,550)	(19,550)			(19,550)
Subsidiary dividends to non-controlling interests	$ (300)							(300)
Balance at end of period, shares at Jun. 30, 2021	290,115		290,115
Balance at end of period, shares at Jun. 30, 2021	(46,151)						(46,151)
Balance at end of period at Jun. 30, 2021	$ 2,583,070	2,554,248	$ 290	1,968,339	788,567	16,113	$ (219,061)	28,822
Balance at beginning of period, shares at Mar. 31, 2021			289,865
Balance at beginning of period, shares at Mar. 31, 2021							(46,151)
Balance at beginning of period at Mar. 31, 2021	2,462,237	2,433,917	$ 290	1,964,331	672,534	15,823	$ (219,061)	28,320
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	126,458	125,806			125,806			652
Other comprehensive income (loss)	290	290				290
Issuance of stock through share-based compensation plans, shares			250
Issuance of stock through share-based compensation plans	1,462	1,462		1,462
Share-based compensation	2,546	2,546		2,546
Cash dividends declared	(9,773)	(9,773)			(9,773)
Subsidiary dividends to non-controlling interests	$ (150)							(150)
Balance at end of period, shares at Jun. 30, 2021	290,115		290,115
Balance at end of period, shares at Jun. 30, 2021	(46,151)						(46,151)
Balance at end of period at Jun. 30, 2021	$ 2,583,070	$ 2,554,248	$ 290	$ 1,968,339	$ 788,567	$ 16,113	$ (219,061)	$ 28,822