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Stock-Based Compensation (Schedule of Fair Value of Employee Share-Based Payments Awards Estimated Using the Assumptions) (Details)
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Stock Option [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Risk-free interest rate 1.72% 0.90% 1.68% 1.10%
Dividend yield 0.00% 0.00% 0.00% 0.00%
Expected volatility 60.00% 67.00% 61.00% 76.00%
Expected life 4 years 3 months 25 days 4 years 4 months 13 days 4 years 2 months 8 days 4 years 4 months 9 days
Employee Stock Purchase Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Risk-free interest rate 0.94% 0.39% 0.77% 0.42%
Dividend yield 0.00% 0.00% 0.00% 0.00%
Expected volatility 60.00% 65.00% 64.00% 69.00%
Expected life 6 months 6 months 6 months 6 months