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Stock-based Compensation - Option Valuation Method (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Weighted average value of options granted in period (in dollars per share) $ 2.57 $ 4.79 $ 6.24
Aggregate fair value of options $ 1,279 $ 4,217 $ 3,249
Expected dividend yield 0.00% 0.00% 0.00%
Expected dividend yield, non-employees directors 0.00% 0.00% 0.00%
Weighted average expected volatility 67.18% 64.42% 68.57%
Weighted average expected volatility, non-employees directors 67.61% 63.46% 64.10%
Weighted average risk-free interest rate 1.48% 1.60% 2.05%
Weighted average risk-free interest rate, non-employees directors 1.41% 1.62% 1.75%
Weighted average expected term (in years) 6 years 29 days 6 years 26 days 6 years 15 days
Weighted average expected term (in years), non-employees directors 5 years 3 months 18 days 5 years 3 months 26 days 5 years 3 months 17 days
Forfeiture rate 5.00% 5.00% 5.00%
Forfeiture rate, non-employees directors 5.00% 5.00% 5.00%