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Stock Compensation Plans - Assumptions Used to Estimate The Fair Value of The Performance-based Stock Options and Restricted Stock Units (Details)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Fair Value, Option, Quantitative Disclosures [Line Items]      
Expected volatility 45.20%    
Employee Stock Option      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Risk-free interest rate, minimum 1.88% 1.06% 0.80%
Risk-free interest rate, maximum 2.02% 1.57% 1.21%
Expected dividend yield 0.00% 0.00% 0.00%
Expected option life 5 years 4 years 3 years
Weighted-average expected volatility 45.20% 46.10% 43.50%
Performance Shares      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Risk-free interest rate, minimum     0.95%
Risk-free interest rate, maximum     1.48%
Expected dividend yield     0.00%
Expected option life     4 years
Expected volatility     44.50%
Weighted-average expected volatility     44.50%