Share-Based Compensation - 2017, 2016 and 2015 Share-Based Compensation Grants (Details) - shares				1 Months Ended	12 Months Ended
	Feb. 24, 2017	Jan. 28, 2016	Jan. 27, 2015	Feb. 28, 2017	Dec. 31, 2017	Dec. 31, 2016
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period				229,976
Restricted Stock Units (RSUs) [Member] | Chief Executive Officer [Member] | Executive officer share-based compensation programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period		294,821	212,468
Market measure-based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period	130,956	168,077	127,657
Time-Based Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period		126,744	84,811	99,020
Time-Based Restricted Stock Units (RSUs) [Member] | Executive officer share-based compensation programs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period					43,081	47,003