Stock-Based Compensation (Schedule of Fair Value of the Restricted Stock Awards Granted During the Periods) (Details) - Restricted Stock [Member] - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016
Time Vested [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		524,903	576,578
Estimated fair value (in millions)	[1]	$ 12.7	$ 3.5
Time Vested [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		475,799	486,578
Estimated fair value (in millions)	[1]	$ 11.8	$ 2.6
Percentage of shares granted expected to be distributed		95.00%	94.00%
Time Vested [Member] | Non-employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		49,104	90,000
Estimated fair value (in millions)	[1]	$ 0.9	$ 0.9
Percentage of shares granted expected to be distributed		100.00%	100.00%
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		173,373	152,373
Estimated fair value (in millions)	[1]	$ 4.5	$ 0.8
Performance Shares [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		173,373	152,373
Estimated fair value (in millions)	[1]	$ 4.5	$ 0.8
Percentage of shares granted expected to be distributed		91.00%	89.00%
Performance Shares [Member] | Non-employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		0	0
Estimated fair value (in millions)	[1]	$ 0.0	$ 0.0

[1] Represents 100% of the grant date fair value. (We recognize the grant date fair value minus estimated forfeitures.)