Pension and Severance Plans (Defined Benefit Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year	$ 109,695	$ 74,009
Service cost	33,854	12,481
Interest cost	3,641	2,954
Benefits paid	(8,499)	(3,924)
Actuarial (gain) loss	(2,801)	(2,631)
Acquisition (Note 3)	0	31,859
Settlement	(1,165)	0
Foreign exchange (gain) loss	(3,309)	(5,053)
Projected benefit obligation at end of year	131,416	109,695	$ 74,009
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	76,042	54,771
Actual gain (loss) on plan assets	2,876	1,564
Employer contributions	25,114	12,190
Acquisition (Note 3)	0	13,935
Settlement	(1,165)	0
Benefits paid	(8,499)	(3,924)
Foreign exchange gain (loss)	(2,897)	(2,494)
Fair value of plan assets at end of year	91,471	76,042	$ 54,771
Funded status of the Plans at end of year	(39,945)	(33,653)
Defined Benefit Plan, Assets for Plan Benefits [Abstract]
Accrued benefit liability (included in pension and severance obligations)	39,900	33,700
Accumulated benefit obligation	94,500	77,600
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Aggregate projected benefit obligation	131,416	101,832
Aggregate fair value of plan assets	91,471	67,622
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Abstract]
Aggregate accumulated benefit obligation	49,285	40,428
Aggregate fair value of plan assets	$ 16,811	$ 13,944
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate for determining net periodic pension cost	3.30%	4.20%	3.90%
Discount rate for determining benefit obligations at year end	3.10%	3.30%	4.20%
Rate of compensation increase for determining net periodic pension cost	3.90%	4.70%	4.10%
Rate of compensation increase for determining benefit obligations at year end	3.80%	3.90%	4.70%
Expected rate of return on plan assets for determining net periodic pension cost	5.00%	6.20%	6.20%