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Incentive Plans (Changes in Performance-Based RSU Outstanding) (Details) - Equity-Settled Restricted Stock Units [Member] - shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Balance at beginning of year 1,103,986 1,397,040 1,560,292
Granted 394,000 455,000 464,300
Awarded (361,096) (521,800) (473,186)
Forfeited (144,317) (226,254) (154,366)
Balance at end of year 992,573 1,103,986 1,397,040