Statement of Consolidated Stockholders' Equity (USD $) In Millions, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2013	$ 1,084.2	$ 0.2	$ 1,023.1	$ 233.8	$ (152.2)	$ (20.7)
Beginning balance, shares at Dec. 31, 2013	18,147,017	18,147,017
Stockholders' Equity [Roll Forward]
Net income	40.3			40.3
Other comprehensive income, net of tax	3.0					3.0
Issuance of non-vested shares to employees, shares		118,638
Issuance of common shares to non-employee directors, shares		2,548
Issuance of common shares to non-employee directors	0.2		0.2
Issuance of common shares to employees upon vesting of restricted stock units and performance shares, shares		44,895
Cancellation of employee non-vested shares		(526)
Cancellation of shares to cover employees’ tax withholdings upon vesting of non-vested shares, shares		(33,006)
Cancellation of shares to cover employees’ tax withholdings upon vesting of non-vested shares	(2.4)		(2.4)
Repurchase of common stock, shares	(346,781)	(346,781)
Repurchase of common stock	(24.0)				(24.0)
Cash dividends on common stock ($0.70 per share)	(12.8)			(12.8)
Excess tax benefit upon vesting of non-vested shares and dividend payment on unvested shares expected to vest	0.8		0.8
Amortization of unearned equity compensation	4.3		4.3
Dividends on unvested equity awards that were canceled	0.1			0.1
Ending balance at Jun. 30, 2014	$ 1,093.7	$ 0.2	$ 1,026.0	$ 261.4	$ (176.2)	$ (17.7)
Ending balance, shares at Jun. 30, 2014	17,932,785	17,932,785