Income Taxes - Foreign Earnings Percentage (Details) - Pre-tax income [Member] - Geographic Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Concentration Risk [Line Items]
Concentration Risk, Percentage	14.00%	11.00%	11.00%
Concentration Risk, Benchmark Description	Pre-tax income, consolidated
Concentration Risk, Additional Characteristic	Foreign operations
South Korea [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	13.00%	11.00%	8.00%
Concentration Risk, Benchmark Description	Pre-tax income, consolidated
Concentration Risk, Additional Characteristic	South Korea