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
	Mar. 31, 2018	Mar. 31, 2017
Share-Based Compensation and Benefit Plans
Profit sharing and savings plan, description	The Company sponsors a contributory profit sharing and savings plan (the “401(k) Plan”) that covers substantially all employees who are at least 21 years of age and have completed one year of service. The Company makes matching contributions equal to 100% of the first 2% of each employee’s wages that are contributed and 25% of the next 4% of each employee’s wages that are contributed.
Profit sharing and savings plan, employer discretionary contribution	$ 0.0	$ 0.0
Profit sharing and savings plan, cost recognized	$ 5.7	$ 5.5
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%