Equity and Accumulated Other Comprehensive Income (Loss) - Changes in Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 1,719,709	$ 1,429,517
Net income	$ 33,184	$ 120,030	43,379	106,062
Other comprehensive income (loss)	(11,186)	(815)	3,866	13,001
Issuance of stock through employee share-based compensation plans			1,023	2,365
Treasury stock acquired through surrender of shares for tax withholding			(105)	(1,378)
Share-based compensation			2,556	2,516
Subsidiary dividends paid to non-controlling interests			(270)	(270)
Ending balance	1,770,158	1,551,813	1,770,158	1,551,813
Attributable to Amkor
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			1,696,276	1,409,692
Net income			42,135	104,227
Other comprehensive income (loss)			3,866	13,001
Issuance of stock through employee share-based compensation plans			1,023	2,365
Treasury stock acquired through surrender of shares for tax withholding			(105)	(1,378)
Share-based compensation			2,556	2,516
Subsidiary dividends paid to non-controlling interests			0	0
Ending balance	1,745,751	1,530,423	1,745,751	1,530,423
Attributable to Non-controlling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			23,433	19,825
Net income			1,244	1,835
Other comprehensive income (loss)			0	0
Issuance of stock through employee share-based compensation plans			0	0
Treasury stock acquired through surrender of shares for tax withholding			0	0
Share-based compensation			0	0
Subsidiary dividends paid to non-controlling interests			(270)	(270)
Ending balance	$ 24,407	$ 21,390	$ 24,407	$ 21,390