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, 2023		63,562,149
BALANCE at period start at Dec. 31, 2023	$ 2,211.4	$ 0.6	$ 22.4	$ 4,643.0	$ (2,454.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	190.1			190.1
Repurchases of common stock, including excise tax	(38.8)				(38.8)
Stock-based compensation expense	14.1		14.1
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	(17.0)		(34.5)	(3.4)	20.9
BALANCE at period end (in shares) at Mar. 31, 2024		63,562,149
BALANCE at period end at Mar. 31, 2024	2,359.8	$ 0.6	2.0	4,829.7	(2,472.5)
BALANCE at period start (in shares) at Dec. 31, 2023		63,562,149
BALANCE at period start at Dec. 31, 2023	2,211.4	$ 0.6	22.4	4,643.0	(2,454.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	506.1
BALANCE at period end (in shares) at Sep. 30, 2024		63,562,149
BALANCE at period end at Sep. 30, 2024	2,371.2	$ 0.6	16.4	5,145.7	(2,791.5)
BALANCE at period start (in shares) at Mar. 31, 2024		63,562,149
BALANCE at period start at Mar. 31, 2024	2,359.8	$ 0.6	2.0	4,829.7	(2,472.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	130.2			130.2
Repurchases of common stock, including excise tax	(314.4)				(314.4)
Stock-based compensation expense	7.6		7.6
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	0.0		(0.8)		0.8
BALANCE at period end (in shares) at Jun. 30, 2024		63,562,149
BALANCE at period end at Jun. 30, 2024	2,183.2	$ 0.6	8.8	4,959.9	(2,786.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	185.8			185.8
Repurchases of common stock, including excise tax	(5.7)				(5.7)
Stock-based compensation expense	8.1		8.1
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	(0.2)		(0.5)		0.3
BALANCE at period end (in shares) at Sep. 30, 2024		63,562,149
BALANCE at period end at Sep. 30, 2024	2,371.2	$ 0.6	16.4	5,145.7	(2,791.5)
BALANCE at period start (in shares) at Dec. 31, 2024		63,562,149
BALANCE at period start at Dec. 31, 2024	2,457.3	$ 0.6	20.3	5,331.8	(2,895.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	175.5			175.5
Repurchases of common stock, including excise tax	(226.6)				(226.6)
Stock-based compensation expense	16.7		16.7
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	(19.7)		(33.7)	(4.8)	18.8
BALANCE at period end (in shares) at Mar. 31, 2025		63,562,149
BALANCE at period end at Mar. 31, 2025	2,403.2	$ 0.6	3.3	5,502.5	(3,103.2)
BALANCE at period start (in shares) at Dec. 31, 2024		63,562,149
BALANCE at period start at Dec. 31, 2024	2,457.3	$ 0.6	20.3	5,331.8	(2,895.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	477.0
BALANCE at period end (in shares) at Sep. 30, 2025		63,562,149
BALANCE at period end at Sep. 30, 2025	2,511.6	$ 0.6	21.3	5,804.0	(3,314.3)
BALANCE at period start (in shares) at Mar. 31, 2025		63,562,149
BALANCE at period start at Mar. 31, 2025	2,403.2	$ 0.6	3.3	5,502.5	(3,103.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	86.4			86.4
Repurchases of common stock, including excise tax	(29.3)				(29.3)
Stock-based compensation expense	8.9		8.9
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	0.3		(0.3)		0.6
BALANCE at period end (in shares) at Jun. 30, 2025		63,562,149
BALANCE at period end at Jun. 30, 2025	2,469.5	$ 0.6	11.9	5,588.9	(3,131.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	215.1			215.1
Repurchases of common stock, including excise tax	(182.8)				(182.8)
Stock-based compensation expense	9.9		9.9
Shares awarded under stock-based compensation plans, net of shares withheld for taxes	(0.1)		(0.5)		0.4
BALANCE at period end (in shares) at Sep. 30, 2025		63,562,149
BALANCE at period end at Sep. 30, 2025	$ 2,511.6	$ 0.6	$ 21.3	$ 5,804.0	$ (3,314.3)