Unaudited Condensed Consolidated Statement Of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock
BALANCE at period start (in shares) at Dec. 31, 2021		86,562,149
BALANCE at period start at Dec. 31, 2021	$ 2,377.0	$ 0.8	$ 3.2	$ 4,639.9	$ (2,266.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	362.1			362.1
Repurchases of common stock, including excise tax	(380.9)				(380.9)
Stock-based compensation expense	15.9		15.9
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	(28.5)		(16.7)	(58.1)	46.3
BALANCE at period end (in shares) at Mar. 31, 2022		86,562,149
BALANCE at period end at Mar. 31, 2022	2,345.6	$ 0.8	2.4	4,943.9	(2,601.5)
BALANCE at period start (in shares) at Dec. 31, 2021		86,562,149
BALANCE at period start at Dec. 31, 2021	2,377.0	$ 0.8	3.2	4,639.9	(2,266.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	738.4
BALANCE at period end (in shares) at Jun. 30, 2022		86,562,149
BALANCE at period end at Jun. 30, 2022	2,325.0	$ 0.8	5.2	5,320.2	(3,001.2)
BALANCE at period start (in shares) at Mar. 31, 2022		86,562,149
BALANCE at period start at Mar. 31, 2022	2,345.6	$ 0.8	2.4	4,943.9	(2,601.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	376.3			376.3
Repurchases of common stock, including excise tax	(403.9)				(403.9)
Stock-based compensation expense	5.3		5.3
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	1.7		(2.5)		4.2
BALANCE at period end (in shares) at Jun. 30, 2022		86,562,149
BALANCE at period end at Jun. 30, 2022	2,325.0	$ 0.8	5.2	5,320.2	(3,001.2)
BALANCE at period start (in shares) at Dec. 31, 2022		63,562,149
BALANCE at period start at Dec. 31, 2022	2,047.8	$ 0.6	3.1	3,663.7	(1,619.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	288.7			288.7
Repurchases of common stock, including excise tax	(307.5)				(307.5)
Stock-based compensation expense	15.1		15.1
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	(23.8)		(15.2)	(41.8)	33.2
BALANCE at period end (in shares) at Mar. 31, 2023		63,562,149
BALANCE at period end at Mar. 31, 2023	2,020.3	$ 0.6	3.0	3,910.6	(1,893.9)
BALANCE at period start (in shares) at Dec. 31, 2022		63,562,149
BALANCE at period start at Dec. 31, 2022	2,047.8	$ 0.6	3.1	3,663.7	(1,619.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	561.2
BALANCE at period end (in shares) at Jun. 30, 2023		63,562,149
BALANCE at period end at Jun. 30, 2023	2,091.8	$ 0.6	11.0	4,183.1	(2,102.9)
BALANCE at period start (in shares) at Mar. 31, 2023		63,562,149
BALANCE at period start at Mar. 31, 2023	2,020.3	$ 0.6	3.0	3,910.6	(1,893.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	272.5			272.5
Repurchases of common stock, including excise tax	(209.5)				(209.5)
Stock-based compensation expense	8.3		8.3
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	0.2		(0.3)		0.5
BALANCE at period end (in shares) at Jun. 30, 2023		63,562,149
BALANCE at period end at Jun. 30, 2023	$ 2,091.8	$ 0.6	$ 11.0	$ 4,183.1	$ (2,102.9)