Condensed Consolidated Statements of Stockholders' 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, 2017	$ 31.9	$ 289.7	$ (24.9)	$ 380.5	$ 677.2
Balance (in shares) at Dec. 31, 2017	42.5
Increase (Decrease) in Stockholders' Equity
Cumulative-effect adjustment recorded to retained earnings			(6.0)	6.0
Net income				14.2	14.2
Other comprehensive income (loss), net of tax			0.2		0.2
Share-based compensation		2.7			2.7
Shares issued	$ 0.1	(4.3)			(4.2)
Shares issued (in shares)	0.2
Dividends ($0.21 and $0.20 per share) for the periods ending March 31, 2019 and 2018 respectively				(8.7)	(8.7)
Balance at the end of the period at Mar. 31, 2018	$ 32.0	288.1	(30.7)	392.0	681.4
Balance (in shares) at Mar. 31, 2018	42.7
Balance at the beginning of the period at Dec. 31, 2018	$ 32.0	297.8	(34.5)	460.0	755.3
Balance (in shares) at Dec. 31, 2018	42.7
Increase (Decrease) in Stockholders' Equity
Cumulative-effect adjustment recorded to retained earnings				4.4	4.4
Net income				12.5	12.5
Other comprehensive income (loss), net of tax			(0.2)		(0.2)
Share-based compensation		3.2			3.2
Shares issued	$ 0.1	(3.2)			(3.1)
Shares issued (in shares)	0.1
Dividends ($0.21 and $0.20 per share) for the periods ending March 31, 2019 and 2018 respectively				(9.1)	(9.1)
Balance at the end of the period at Mar. 31, 2019	$ 32.1	$ 297.8	$ (34.7)	$ 467.8	$ 763.0
Balance (in shares) at Mar. 31, 2019	42.8