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, 2020	$ 32.4	$ 321.5	$ (50.8)	$ 658.1	$ 961.2
Balance (in shares) at Dec. 31, 2020	43.2
Increase (Decrease) in Shareholders' Equity
Net income				87.2	87.2
Other comprehensive income (loss), net of tax			(0.1)		(0.1)
Share-based compensation		4.8			4.8
Shares issued, net of shares withheld for employee taxes	$ 0.2	(14.3)			(14.1)
Shares issued, net of shares withheld for employee taxes (in shares)	0.2
Dividends				(10.1)	(10.1)
Balance at the end of the period at Mar. 31, 2021	$ 32.6	312.0	(50.9)	735.2	1,028.9
Balance (in shares) at Mar. 31, 2021	43.4
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)				(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