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Stock Incentive Plan (Schedule of Nonvested Restricted Stock Units Activity) (Details) - Restricted Stock Units (RSUs) - shares
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 [Roll Forward]      
RSUs granted and unvested at beginning of period: 4,124,260 5,062,661 5,216,972
Granted 962,453 840,796 1,140,048
Vested (1,111,588) (1,447,522) (900,254)
Canceled (170,789) (331,675) (394,105)
RSUs granted and unvested at end of period: 3,804,336 4,124,260 5,062,661