Share-Based Compensation and Benefit Plans (Profit Sharing and Savings Plan) (Narrative) (Details) - Profit sharing and savings plan [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-Based Compensation and Benefit Plans
Profit sharing and savings plan, employer discretionary contribution	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Profit sharing and savings plan, cost recognized	$ 6.5	$ 6.2	$ 12.6	$ 11.9
Employee's first 2% of contributed wages [Member]
Share-Based Compensation and Benefit Plans
Profit sharing and savings plan, Company match			100.00%
Employee's next 4% of contributed wages [Member]
Share-Based Compensation and Benefit Plans
Profit sharing and savings plan, Company match			25.00%