New Accounting Standards Adjustment for new accounting pronouncement (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2016	Dec. 31, 2015
Income Statement:
Net sales	$ 1,081,271	$ 1,144,192	$ 1,065,684	$ 1,025,319	$ 1,150,478	$ 1,148,884	$ 1,008,385	$ 899,284	$ 4,316,466	$ 4,207,031	$ 3,927,849
Cost of sales									3,605,901	3,445,952	3,217,958
Gross Profit	182,370	200,707	169,717	157,771	224,341	223,888	176,616	136,234	710,565	761,079	709,891
Income tax expense	28,812	14,326	10,631	2,481	(13,613)	21,263	33,466	(1,325)	56,250	39,791	51,042
Net income	28,894	57,292	33,184	10,195	101,185	60,458	120,030	(13,968)	129,565	267,705	178,653
Net income attributable to Amkor	$ 28,295	$ 56,662	$ 32,591	$ 9,544	$ 100,059	$ 59,264	$ 119,013	$ (14,786)	$ 127,092	$ 263,550	$ 175,530
Diluted (in dollars per share)	$ 0.12	$ 0.24	$ 0.14	$ 0.04	$ 0.42	$ 0.25	$ 0.50	$ (0.06)	$ 0.53	$ 1.10	$ 0.74
Balance Sheet:
Accounts receivable, net	$ 724,456				$ 798,264				$ 724,456	$ 798,264
Inventories	230,589				213,649				230,589	213,649
Other Assets, Noncurrent	144,178				139,796				144,178	139,796
Accrued expenses	258,209				330,868				258,209	330,868
Other non-current liabilities	79,071				47,823				79,071	47,823
Accumulated deficit	113,189				(13,903)				113,189	(13,903)
Cumulative effect adjustment from standard adoption												$ 14,764
Operating income	$ 75,381	$ 92,703	$ 53,941	$ 36,119	109,018	$ 105,479	$ 172,659	$ 18,384	258,144	405,540	$ 308,587
As Previously Reported
Income Statement:
Net sales										4,186,497	3,893,635
Cost of sales										3,429,224	3,198,158
Gross Profit										757,273	695,477
Income tax expense										38,982	47,853
Net income										264,888	167,304
Net income attributable to Amkor										$ 260,706	$ 164,190
Diluted (in dollars per share)										$ 1.09	$ 0.69
Balance Sheet:
Accounts receivable, net					692,287					$ 692,287
Inventories					326,492					326,492
Other Assets, Noncurrent					146,051					146,051
Accrued expenses					374,598					374,598
Other non-current liabilities					46,144					46,144
Accumulated deficit					(42,851)					(42,851)
Accounting Standards Update 2017-07
Balance Sheet:
Operating income										(600)	$ (100)
Accounting Standards Update 2014-09
Income Statement:
Net sales										4,207,031	3,927,849
Cost of sales										3,445,952	3,217,958
Gross Profit										761,079	709,891
Income tax expense										39,791	51,042
Net income										267,705	178,653
Net income attributable to Amkor										$ 263,550	$ 175,530
Diluted (in dollars per share)										$ 1.10	$ 0.74
Balance Sheet:
Accounts receivable, net					798,264					$ 798,264
Inventories					213,649					213,649
Other Assets, Noncurrent					139,796					139,796
Accrued expenses					330,868					330,868
Other non-current liabilities					47,823					47,823
Accumulated deficit					(13,903)					(13,903)
New Accounting Pronouncement Adjustment | Accounting Standards Update 2014-09
Income Statement:
Net sales										20,534	$ 34,214
Cost of sales										16,728	19,800
Gross Profit										3,806	14,414
Income tax expense										809	3,189
Net income										2,817	11,349
Net income attributable to Amkor										$ 2,844	$ 11,340
Diluted (in dollars per share)										$ 0.01	$ 0.05
Balance Sheet:
Accounts receivable, net					105,977					$ 105,977
Inventories					(112,843)					(112,843)
Other Assets, Noncurrent					(6,255)					(6,255)
Accrued expenses					(43,730)					(43,730)
Other non-current liabilities					1,679					1,679
Accumulated deficit					28,948					28,948
Retained Earnings (Accumulated Deficit)
Income Statement:
Net income attributable to Amkor									$ 127,092	263,550	$ 175,530
Balance Sheet:
Cumulative effect adjustment from standard adoption												$ 14,764
Retained Earnings (Accumulated Deficit) | Accounting Standards Update 2014-09 | Restatement
Balance Sheet:
Cumulative effect adjustment from standard adoption					$ 2,800					$ 2,800	$ 11,300		$ 14,800