Debt (Interest Rates) (Details)	Dec. 31, 2018	Dec. 31, 2017
Term loan, LIBOR plus 1.80% due December 2019 | China
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	4.22%	3.16%
Subsidiary Term Loans | Term loan, LIBOR plus 2.70%, due December 2019 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	4.02%
Subsidiary Term Loans | Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 (2) | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	4.06%
Subsidiary Term Loans | Term loan, fund floating rate plus 1.60%, due June 2020 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	4.49%	3.29%
Subsidiary Term Loans | Term loan, LIBOR plus 2.56%, due December 2023 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	5.38%	0.00%
Subsidiary Term Loans | Term loan, applicable bank rate plus 1.98%, due December 2028 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	4.64%	0.00%
Revolving Credit Facility | Line of Credit | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due September 2018 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	4.01%
Revolving Credit Facility | Line of Credit | $30 million revolving credit facility, LIBOR plus the applicable bank rate, due October 2019 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	0.00%
Revolving Credit Facility | Line of Credit | Short-term term loans, variable rates | Japan
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.24%	0.22%
Revolving Credit Facility | Line of Credit | $250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore)
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	0.00%
Revolving Credit Facility | Line of Credit | Revolving credit facility, TAIFX plus a bank-determined spread, due November 2020 (Taiwan) | Taiwan
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	4.26%	3.18%