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Stock-Based Compensation (Valuation Assumptions) (Details) - Stock options [Member] - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected term (in years) (1) 5 years 2 months 12 days 5 years 2 months 12 days 5 years 4 months 10 days 6 years
Volatility 63.00% 67.00% 65.00% 66.00%
Risk-free interest rate 1.18% 1.64% 1.29% 1.70%
Dividend yield 0.00% 0.00% 0.00% 0.00%
Weighted-average estimated fair value of stock options granted (usd per share) $ 2.25 $ 2.31 $ 2.30 $ 2.09