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Stock-Based Compensation (Valuation Assumptions) (Details) - Stock options [Member] - $ / shares
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term (in years) 5 years 4 months 2 days 5 years 4 months 12 days
Volatility 62.00% 65.00%
Risk-free interest rate 2.00% 1.30%
Dividend yield 0.00% 0.00%
Weighted-average estimated fair value of stock options granted (usd per share) $ 2.52 $ 2.31