XML 76 R49.htm IDEA: XBRL DOCUMENT v3.20.1
Stock-Based Compensation - Valuation Assumptions for Stock Options (Details) - Common stock options - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected life (in years) 5 years 8 months 12 days 5 years 7 months 6 days 5 years 7 months 6 days
Volatility 62.90% 56.50% 51.30%
Risk-free interest rate 2.30% 2.70% 1.90%
Dividend yield 0.00% 0.00% 0.00%
Weighted-average grant-date fair value per stock option (usd per share) $ 6.48 $ 10.66 $ 25.13