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				6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Time Vested [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	49,312		63,104		888,810		524,903
Estimated fair value (in millions)	$ 1.0	[1]	$ 1.3	[1]	$ 17.1	[2]	$ 12.7	[2]
Time Vested [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	5,000		14,000		844,498		475,799
Estimated fair value (in millions)	$ 0.1	[1]	$ 0.4	[1]	$ 16.2	[2]	$ 11.8	[2]
Percentage of shares granted expected to be distributed	95.00%		100.00%		95.00%		95.00%
Time Vested [Member] | Non-employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	44,312		49,104		44,312		49,104
Estimated fair value (in millions)	$ 0.9	[1]	$ 0.9	[1]	$ 0.9	[2]	$ 0.9	[2]
Percentage of shares granted expected to be distributed	100.00%		100.00%		100.00%		100.00%
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	0		21,000		362,070		173,373
Estimated fair value (in millions)	$ 0.0	[1]	$ 0.5	[1]	$ 7.3	[2]	$ 4.5	[2]
Performance Shares [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	0		21,000		362,070		173,373
Estimated fair value (in millions)	$ 0.0	[1]	$ 0.5	[1]	$ 7.3	[2]	$ 4.5	[2]
Percentage of shares granted expected to be distributed			87.00%		62.00%		87.00%
Performance Shares [Member] | Non-employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	0		0		0		0
Estimated fair value (in millions)	$ 0.0	[1]	$ 0.0	[1]	$ 0.0	[2]	$ 0.0	[2]

[1] The performance shares represent 100% of the grant date fair value. (We recognize the grant date fair value minus estimated forfeitures.)

[2] The performance shares represent 100% of the grant date fair value. (We recognize the grant date fair value minus estimated forfeitures.)