Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 264,888	$ 167,304	$ 53,893
Other comprehensive income (loss), net of tax:
Adjustments to unrealized components of defined benefit pension plans	5,165	2,563	1,100
Foreign currency translation	11,092	5,783	(146)
Equity interest in J-Devices' other comprehensive income (loss)	0	0	29,433
Total other comprehensive income (loss)	16,257	8,346	30,387
Comprehensive income	281,145	175,650	84,280
Comprehensive income attributable to noncontrolling interests	(4,182)	(3,114)	(2,795)
Comprehensive income attributable to Amkor	$ 276,963	$ 172,536	$ 81,485