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% |