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Share-Based Payments - Performance Share Awards (PSAs) Narrative (Details) - Performance Shares [Member]
12 Months Ended
Dec. 31, 2018
measure
period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of measures used to determine share payout | measure 2
Share payout measures, operating income, number of periods | period 3
Share payout measures, operating income, duration of period 1 year
Award vesting period 3 years
Minimum [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of shares earned as a percentage of initial award 0.00%
Maximum [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of shares earned as a percentage of initial award 200.00%