Pension and Severance Plans (Defined Benefit Plans - Allocation of plan assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 115,725	$ 91,471	$ 76,042
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55,873	34,145
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33,699	35,304
Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,098	10,419
Level 1 | US Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16,854	12,602
Level 1 | Foreign Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16,826	8,825
Level 1 | Foreign Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22,193	12,718
Level 1 | US Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,188	2,859
Level 1 | U.S. Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,144	1,980
Level 1 | Foreign Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,211	11,001
Level 1 | Foreign Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	520	0
Level 1 | Foreign Treasury Notes [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,686	0
Level 1 | Foreign Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,787	10,044
Level 1 | Taiwan Retirement Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10,094	8,972
Level 1 | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	584	0
Level 2 | US Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	830	0
Level 2 | U.S. Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	0
Level 2 | Foreign Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,270	7,727
Level 2 | Foreign Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,058	1,693
Level 2 | Foreign Guaranteed Investment Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14,138	2,445
Level 2 | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 239	$ 186
Japan | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	37.00%
Japan | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	60.00%
Japan | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	3.00%
Korea | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	50.00%
Korea | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	40.00%
Korea | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	10.00%
Philippines | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	56.00%
Philippines | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	40.00%
Philippines | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	4.00%