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Stock-Based Compensation - Valuation Assumptions (Details) - Options
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Assumptions used in estimation of fair value of the share-based payment awards on the grant date      
Risk-free interest rate, minimum (as a percent) 1.00% 0.60% 1.30%
Risk-free interest rate, maximum (as a percent) 2.10% 1.70% 1.70%
Volatility, minimum (as a percent) 61.40% 55.70% 53.70%
Volatility, maximum (as a percent) 65.00% 59.30% 57.50%
Dividend yield (as a percent) 0.00% 0.00% 0.00%
Minimum      
Assumptions used in estimation of fair value of the share-based payment awards on the grant date      
Expected life 3 years 3 years 4 years
Maximum      
Assumptions used in estimation of fair value of the share-based payment awards on the grant date      
Expected life 5 years 5 years 5 years