Stock-Based Compensation (Schedule of Fair Value of the Restricted Stock Awards Granted During the Periods) (Details) - Restricted Stock [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Time Vested [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		925,673	839,498
Estimated fair value (in millions)	[1]	$ 14.6	$ 16.1
Time Vested [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		925,673	839,498
Estimated fair value (in millions)	[1]	$ 14.6	$ 16.1
Percentage of shares granted expected to be distributed		95.00%	95.00%
Time Vested [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
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		424,070	362,070
Estimated fair value (in millions)	[1]	$ 7.1	$ 7.3
Performance Shares [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		424,070	362,070
Estimated fair value (in millions)	[1]	$ 7.1	$ 7.3
Percentage of shares granted expected to be distributed		64.00%	63.00%
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] The performance shares represent 100% of the grant date fair value. (We recognize the grant date fair value minus estimated forfeitures.)