New Accounting Standards - Revenue from Contracts with Customers (Topic 606) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	$ 1,025,319	$ 899,284
Cost of sales	867,548	763,050
Gross profit	157,771	136,234
Income tax expense (benefit)	2,481	(1,325)
Net loss	10,195	(13,968)
Net loss attributable to Amkor	$ 9,544	$ (14,786)
Net loss attributable to Amkor per common share - diluted (in dollars per share)	$ 0.04	$ (0.06)
Accounts receivable, net	$ 734,953		$ 798,264
Inventories	228,611		213,649
Other assets	142,041		139,796
Accrued expenses	311,408		330,868
Other non-current liabilities	45,234		47,823
Accumulated deficit (1)	$ (4,359)		(13,903)
As Previously Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales		$ 913,600
Cost of sales		770,694
Gross profit		142,906
Income tax expense (benefit)		439
Net loss		(9,144)
Net loss attributable to Amkor		$ (10,006)
Net loss attributable to Amkor per common share - diluted (in dollars per share)		$ (0.04)
Accounts receivable, net			692,287
Inventories			326,492
Other assets			146,051
Accrued expenses			374,598
Other non-current liabilities			46,144
Accumulated deficit (1)			(42,851)
New Accounting Pronouncement Adjustment | ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales		$ (14,316)
Cost of sales		(7,644)
Gross profit		(6,672)
Income tax expense (benefit)		(1,764)
Net loss		(4,824)
Net loss attributable to Amkor		$ (4,780)
Net loss attributable to Amkor per common share - diluted (in dollars per share)		$ (0.02)
Accounts receivable, net			105,977
Inventories			(112,843)
Other assets			(6,255)
Accrued expenses			(43,730)
Other non-current liabilities			1,679
Accumulated deficit (1)			28,948
New Accounting Pronouncement Adjustment | ASU 2014-09 | Adjustment to Accumulated Deficit
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Adjustment to accumulated deficit			$ 2,800	$ 11,300	$ 14,800