CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS’ EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2022		43,593,809
Beginning balance at Dec. 31, 2022	$ 2,903.5	$ 0.4	$ 1,281.4	$ 2,610.1	$ (1,063.0)	$ 74.4
Treasury stock, beginning balance (in shares) at Dec. 31, 2022					22,024,479
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	181.4			181.4
Change in fair value of cash flow swaps, net of reclassification adjustment	(14.6)					(14.6)
Unrealized gain on changes in fair value of debt securities, net of reclassification adjustment and tax expense	2.0					2.0
Comprehensive income	168.7			181.4		(12.6)
Share-based compensation	8.6		8.6
Issuance of common stock, net of forfeitures in connection with share-based payment arrangements (in shares)		120,575
Shares repurchased (in shares)					110,323
Share repurchases	(20.7)				$ (20.7)
Repurchase of common stock associated with net share settlements of employee share-based awards (in shares)					45,613
Repurchase of common stock associated with net share settlement of employee share-based awards	(10.9)				$ (10.9)
Retirement of common stock (in shares)		(164,527)			(164,527)
Retirement of common stock	0.0		(2.0)	(28.2)	$ 30.2
Ending balance (in shares) at Mar. 31, 2023		43,549,857
Ending balance at Mar. 31, 2023	3,049.2	$ 0.4	1,288.0	2,763.3	$ (1,064.3)	61.8
Treasury stock, ending balance (in shares) at Mar. 31, 2023					22,015,888
Beginning balance (in shares) at Dec. 31, 2022		43,593,809
Beginning balance at Dec. 31, 2022	2,903.5	$ 0.4	1,281.4	2,610.1	$ (1,063.0)	74.4
Treasury stock, beginning balance (in shares) at Dec. 31, 2022					22,024,479
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	377.7
Comprehensive income	$ 374.7
Shares repurchased (in shares)	1,070,126
Ending balance (in shares) at Jun. 30, 2023		42,591,097
Ending balance at Jun. 30, 2023	$ 3,068.6	$ 0.4	1,282.0	2,781.1	$ (1,066.4)	71.4
Treasury stock, ending balance (in shares) at Jun. 30, 2023					22,016,267
Beginning balance (in shares) at Mar. 31, 2023		43,549,857
Beginning balance at Mar. 31, 2023	3,049.2	$ 0.4	1,288.0	2,763.3	$ (1,064.3)	61.8
Treasury stock, beginning balance (in shares) at Mar. 31, 2023					22,015,888
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	196.4			196.4
Change in fair value of cash flow swaps, net of reclassification adjustment	12.8					12.8
Unrealized gain on changes in fair value of debt securities, net of reclassification adjustment and tax expense	(3.2)					(3.2)
Comprehensive income	206.0			196.4		9.6
Share-based compensation	$ 5.5		5.5
Issuance of common stock, net of forfeitures in connection with share-based payment arrangements (in shares)		1,043
Shares repurchased (in shares)	959,803				959,803
Share repurchases	$ (192.1)				$ (192.1)
Repurchase of common stock associated with net share settlements of employee share-based awards (in shares)					379
Repurchase of common stock associated with net share settlement of employee share-based awards	(0.1)				$ (0.1)
Retirement of common stock (in shares)		(959,803)			(959,803)
Retirement of common stock	0.0		(11.6)	(178.5)	$ 190.1
Ending balance (in shares) at Jun. 30, 2023		42,591,097
Ending balance at Jun. 30, 2023	3,068.6	$ 0.4	1,282.0	2,781.1	$ (1,066.4)	71.4
Treasury stock, ending balance (in shares) at Jun. 30, 2023					22,016,267
Beginning balance (in shares) at Dec. 31, 2023		42,352,001
Beginning balance at Dec. 31, 2023	$ 3,244.1	$ 0.4	1,288.4	2,961.5	$ (1,067.3)	61.1
Treasury stock, beginning balance (in shares) at Dec. 31, 2023	22,018,537				22,018,537
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 147.1			147.1
Change in fair value of cash flow swaps, net of reclassification adjustment	7.5					7.5
Unrealized gain on changes in fair value of debt securities, net of reclassification adjustment and tax expense	(2.2)					(2.2)
Comprehensive income	152.4			147.1		5.3
Share-based compensation	10.5		10.5
Issuance of common stock, net of forfeitures in connection with share-based payment arrangements (in shares)		123,845
Shares repurchased (in shares)					239,790
Share repurchases	(50.4)				$ (50.4)
Repurchase of common stock associated with net share settlements of employee share-based awards (in shares)					45,399
Repurchase of common stock associated with net share settlement of employee share-based awards	(9.8)				$ (9.8)
Retirement of common stock (in shares)		(239,790)			(239,790)
Retirement of common stock	0.0		(2.9)	(47.1)	$ 50.0
Ending balance (in shares) at Mar. 31, 2024		42,236,056
Ending balance at Mar. 31, 2024	3,346.9	$ 0.4	1,296.1	3,061.5	$ (1,077.5)	66.4
Treasury stock, ending balance (in shares) at Mar. 31, 2024					22,063,936
Beginning balance (in shares) at Dec. 31, 2023		42,352,001
Beginning balance at Dec. 31, 2023	$ 3,244.1	$ 0.4	1,288.4	2,961.5	$ (1,067.3)	61.1
Treasury stock, beginning balance (in shares) at Dec. 31, 2023	22,018,537				22,018,537
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 175.2
Comprehensive income	$ 178.8
Shares repurchased (in shares)	432,389
Ending balance (in shares) at Jun. 30, 2024		42,044,298
Ending balance at Jun. 30, 2024	$ 3,330.7	$ 0.4	1,299.5	3,048.7	$ (1,082.5)	64.7
Treasury stock, ending balance (in shares) at Jun. 30, 2024	22,064,198				22,064,198
Beginning balance (in shares) at Mar. 31, 2024		42,236,056
Beginning balance at Mar. 31, 2024	$ 3,346.9	$ 0.4	1,296.1	3,061.5	$ (1,077.5)	66.4
Treasury stock, beginning balance (in shares) at Mar. 31, 2024					22,063,936
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	28.1			28.1
Change in fair value of cash flow swaps, net of reclassification adjustment	(0.4)					(0.4)
Unrealized gain on changes in fair value of debt securities, net of reclassification adjustment and tax expense	(1.3)					(1.3)
Comprehensive income	26.4			28.1		(1.7)
Share-based compensation	$ 5.7		5.7
Issuance of common stock, net of forfeitures in connection with share-based payment arrangements (in shares)		841
Shares repurchased (in shares)	192,599				192,599
Share repurchases	$ (48.2)				$ (48.2)
Repurchase of common stock associated with net share settlements of employee share-based awards (in shares)					262
Repurchase of common stock associated with net share settlement of employee share-based awards	(0.1)				$ (0.1)
Retirement of common stock (in shares)		(192,599)			(192,599)
Retirement of common stock	0.0		(2.3)	(40.9)	$ 43.2
Ending balance (in shares) at Jun. 30, 2024		42,044,298
Ending balance at Jun. 30, 2024	$ 3,330.7	$ 0.4	$ 1,299.5	$ 3,048.7	$ (1,082.5)	$ 64.7
Treasury stock, ending balance (in shares) at Jun. 30, 2024	22,064,198				22,064,198