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Stock Plans (Fair Value of "Look Back" Option for ESPP Weighted-Average Assumptions) (Details) - Employee Stock Purchase Plan - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Schedule of stock options and employee stock purchase plan weighted-average assumptions      
Expected dividends 0.00% 0.00% 0.00%
Stock price on valuation date $ 5.97 $ 8.47 $ 7.77
Expected volatility 57.00% 77.00% 46.00%
Risk-free interest rate 0.29% 0.08% 0.07%
Expected life (in years) 6 months 4 months 25 days 3 months
Fair value per unit $ 1.86 $ 4.56 $ 2.45