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Stock-based Compensation - Performance Share Units Activity (Details) - Performance Share Units [Member] - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Non-vested, beginning balance, shares 529 1,107 987
Granted, shares 542 240 139
Vested, shares (176) (761) (19)
Forfeited, shares (51) (57)  
Non-vested, ending balance, shares 844 529 1,107
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]      
Non-vested, weighted average grant date fair value, beginning balance (in dollars per share) $ 39.53 $ 17.71 $ 12.94
Granted, weighted average grant date fair value (in dollars per share) 17.14 44.38 52.34
Vested, weighted average grant date fair value (in dollars per share) 35.84 5.07 24.16
Forfeited, weighted average grant date fair value (in dollars per share) 27.79 43.35  
Non-vested, weighted average grant date fair value, ending balance (in dollars per share) $ 29.05 $ 39.53 $ 17.71