Equity and Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, Beginning balance	$ 1,130,936	$ 964,940
Net income	29,697	21,183
Other comprehensive income (loss)	1,238	3,949
Issuance of stock through employee share-based compensation plans	574	438
Treasury stock acquired through surrender of shares for tax withholding	(230)	(122)
Share-based compensation expense	1,369	972
Equity, Ending balance	1,163,584	991,360
Amkor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, Beginning balance	1,116,235	953,740
Net income	28,781	20,633
Other comprehensive income (loss)	1,238	3,949
Issuance of stock through employee share-based compensation plans	574	438
Treasury stock acquired through surrender of shares for tax withholding	(230)	(122)
Share-based compensation expense	1,369	972
Equity, Ending balance	1,147,967	979,610
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity, Beginning balance	14,701	11,200
Net income	916	550
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 expense	0	0
Equity, Ending balance	$ 15,617	$ 11,750