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, 2018			285,352
Balance at beginning of period, shares at Dec. 31, 2018							(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)	(31,674)	(32,329)			(32,329)			655
Other comprehensive income (loss)	3,505	3,505				3,505
Treasury stock acquired through surrender of shares for tax withholding, shares							(11)
Treasury stock acquired through surrender of shares for tax withholding	(83)	(83)					$ (83)
Issuance of stock through share-based compensation plans, shares			158
Issuance of stock through share-based compensation plans	436	436		436
Share-based compensation	3,242	3,242		3,242
Subsidiary dividends to noncontrolling interests	(150)							(150)
Balance at end of period, shares at Jun. 30, 2019			285,510
Balance at end of period, shares at Jun. 30, 2019							(45,978)
Balance at end of period at Jun. 30, 2019	1,831,176	1,805,311	$ 285	1,913,103	80,860	27,317	$ (216,254)	25,865
Balance at beginning of period, shares at Mar. 31, 2019			285,430
Balance at beginning of period, shares at Mar. 31, 2019							(45,972)
Balance at beginning of period at Mar. 31, 2019	1,832,582	1,807,011	$ 285	1,911,179	90,310	21,456	$ (216,219)	25,571
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(9,006)	(9,450)			(9,450)			444
Other comprehensive income (loss)	5,861	5,861				5,861
Treasury stock acquired through surrender of shares for tax withholding, shares							(6)
Treasury stock acquired through surrender of shares for tax withholding	(35)	(35)					$ (35)
Issuance of stock through share-based compensation plans, shares			80
Issuance of stock through share-based compensation plans	150	150		150
Share-based compensation	1,774	1,774		1,774
Subsidiary dividends to noncontrolling interests	(150)							(150)
Balance at end of period, shares at Jun. 30, 2019			285,510
Balance at end of period, shares at Jun. 30, 2019							(45,978)
Balance at end of period at Jun. 30, 2019	$ 1,831,176	1,805,311	$ 285	1,913,103	80,860	27,317	$ (216,254)	25,865
Balance at beginning of period, shares at Dec. 31, 2019	286,877		286,877
Balance at beginning of period, shares at Dec. 31, 2019	(46,072)						(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 (loss)	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 noncontrolling interests	$ (300)							(300)
Balance at end of period, shares at Jun. 30, 2020	287,319		287,319
Balance at end of period, shares at Jun. 30, 2020	(46,083)						(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 (loss)	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 noncontrolling interests	$ (300)							(300)
Balance at end of period, shares at Jun. 30, 2020	287,319		287,319
Balance at end of period, shares at Jun. 30, 2020	(46,083)						(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