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Stockholders’ Equity - Black-Scholes Assumptions (Details) - Stock options - $ / shares
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Weighted-average assumptions        
Expected stock price volatility 53.20% 43.60% 49.20% 43.40%
Risk-free interest rate 1.70% 1.20% 1.70% 1.20%
Expected life of options (in years) 4 years 18 days 4 years 4 years 11 days 4 years
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Weighted-average fair value (grant date) of the options (in dollars per share) $ 6.87 $ 12.49 $ 7.79 $ 11.07