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Share-Based Compensation Schedule Of Performance Share Unit Transactions (Details) - Performance Share Units [Member] - $ / shares
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]    
Unvested balance at beginning of period 1,199,336  
Shares granted 724,095  
Shares vested (229,620)  
Unvested balance at end of period 1,693,811  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]    
Weighted average grant date fair value, beginning of period $ 14.59  
Weighted average grant date fair value, grants 9.55 $ 16.98
Weighted average grant date fair value, vested 21.69  
Weighted average grant date fair value, end of period $ 11.47