Share-Based Compensation and Benefit Plans (Profit Sharing and Savings Plan) (Narrative) (Detail) - Profit sharing and savings plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-Based Compensation and Benefit Plans
Profit sharing and savings plan, employer discretionary contribution	$ 0.0	$ 0.0	$ 0.0
Profit sharing and savings plan, cost recognized	$ 31.0	$ 27.5	$ 24.8
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%