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Equity Compensation Plans - Grant Date Fair Value (Details) - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Employee Consultants and Directors Stock Options [Member]      
Stock Option Disclosures      
Weighted average estimated grant date fair value per share $ 18.07 $ 15.05 $ 8.41
Restricted and Performance Stock Units [Member]      
Stock Option Disclosures      
Weighted average estimated grant date fair value per share $ 17.60 $ 23.34 $ 26.24