Statement of Consolidated Stockholders' Equity - USD ($) $ in Millions		Total	Common Stock	Additional Paid in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss
Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment	[1]	$ 0.7		$ 0.8	$ (0.1)
Beginning balance, shares (Scenario, Previously Reported) at Dec. 31, 2015			18,053,747
Beginning balance, shares at Dec. 31, 2015		18,053,747	18,053,747
Beginning balance (Scenario, Previously Reported) at Dec. 31, 2015		$ 774.4	$ 0.2	1,036.5	15.9	$ (246.5)	$ (31.7)
Beginning balance at Dec. 31, 2015		775.1	$ 0.2	1,037.3	15.8	(246.5)	(31.7)
Stockholders' Equity [Roll Forward]
Net income		67.2			67.2
Other comprehensive income, net of tax		2.9					2.9
Issuance of non-vested shares to employees and non-employee directors, shares			9,702
Issuance of common shares to non-employee directors, shares			1,474
Issuance of common shares to non-employee directors		0.1		0.1
Issuance of common shares to employees upon option exercises and vesting of restricted stock units and performance shares, shares			64,476
Issuance of common shares to employees upon option exercises and vesting of restricted stock units and performance shares				1.0
Cancellation of employee non-vested shares, shares			(379)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares			(35,498)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		$ (2.8)		(2.8)
Repurchase of common stock, shares		(170,304)	(170,304)
Repurchase of common stock		$ (13.8)				(13.8)
Cash dividends on common stock ($1.35 per share)		(24.4)			(24.4)
Amortization of unearned equity compensation		8.7		8.7
Dividends on unvested equity awards that were canceled		$ 0.1			0.1
Ending balance, shares at Sep. 30, 2016		17,923,218	17,923,218
Ending balance at Sep. 30, 2016		$ 814.1	$ 0.2	$ 1,044.3	$ 58.7	$ (260.3)	$ (28.8)

[1] See Note 4 and Note 6 for discussion of our adoption of ASU 2016-09 (as defined in Note 1).