Condensed Consolidated Statements of Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Common Stock	Additional Paid In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Total
Balance at the beginning of the period at Dec. 31, 2021	$ 30.7	$ 314.1	$ (30.9)	$ 1,353.5	$ 1,667.4
Balance (in shares) at Dec. 31, 2021	41.0
Increase (Decrease) in Shareholders' Equity
Net income				339.2	339.2
Other comprehensive income (loss), net of tax			0.2		0.2
Share-based compensation		4.7			4.7
Shares issued, net of shares withheld for employee taxes	$ 0.2	(19.5)			(19.3)
Shares issued, net of shares withheld for employee taxes (in shares)	0.2
Shares repurchased	$ (0.5)	(3.1)		(65.0)	(68.6)
Shares repurchased (in shares)	(0.7)
Dividends				(12.9)	(12.9)
Balance at the end of the period at Mar. 31, 2022	$ 30.4	296.2	(30.7)	1,614.8	1,910.7
Balance (in shares) at Mar. 31, 2022	40.5
Balance at the beginning of the period at Dec. 31, 2022	$ 27.2	290.4	(6.9)	1,986.2	2,296.9
Balance (in shares) at Dec. 31, 2022	36.3
Increase (Decrease) in Shareholders' Equity
Net income				34.0	34.0
Other comprehensive income (loss), net of tax			0.6		0.6
Share-based compensation		4.6			4.6
Shares issued, net of shares withheld for employee taxes	$ 0.2	(12.6)			(12.4)
Shares issued, net of shares withheld for employee taxes (in shares)	0.3
Shares repurchased	$ (0.5)	(2.7)		(38.9)	$ (42.1)
Shares repurchased (in shares)	(0.7)				(0.7)
Dividends				(11.3)	$ (11.3)
Balance at the end of the period at Mar. 31, 2023	$ 26.9	$ 279.7	$ (6.3)	$ 1,970.0	$ 2,270.3
Balance (in shares) at Mar. 31, 2023	35.9