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Stock-based Compensation - Weighted-average Assumptions (Details) - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Black-Scholes-Merton option valuation model based on weighted-average assumptions [Abstract]    
Expected term 6 years 6 years
Risk-free interest rate 1.75% 1.58%
Volatility 77.56% 75.07%
Resulting weighted average grant date fair value (in dollars per share) $ 1.84 $ 4.50