Statement of Consolidated Stockholders' Equity - USD ($) $ in Millions		Total	Common Stock	Additional Paid In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss	Before Cumulative Adjustment	Before Cumulative Adjustment Common Stock	Before Cumulative Adjustment Additional Paid In Capital	Before Cumulative Adjustment Retained Earnings	Before Cumulative Adjustment Treasury Stock	Before Cumulative Adjustment Accumulated Other Comprehensive Loss
Beginning balance, shares at Dec. 31, 2015									18,053,747
Beginning balance at Dec. 31, 2015								$ 774.4	$ 0.2	$ 1,036.5	$ 15.9	$ (246.5)	$ (31.7)
Stockholders' Equity [Roll Forward]
Net income		$ 91.7			$ 91.7
Other comprehensive income (loss), net of tax		(5.0)					$ (5.0)
Issuance of non-vested shares to employees			9,702
Issuance of common shares to non-employee directors		0.1		$ 0.1
Issuance of common shares to directors, shares			1,474
Issuance of common shares to employees upon vesting of restricted stock units and performance shares, shares			66,810
Issuance of common shares to employees upon option exercises and vesting of restricted stock units and performance shares		1.2		1.2
Cancellation of employee non-vested shares, shares			(379)
Cancellation of shares to cover employees’ tax withholdings upon vesting of non-vested shares, shares			(36,055)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		$ (2.9)		(2.9)
Repurchase of common stock, shares		(443,838)	(443,838)
Repurchase of common stock		$ (34.9)				$ (34.9)
Cash dividends on common stock	[1]	(32.4)			(32.4)
Amortization of unearned equity compensation		11.7		11.7
Dividends on unvested equity awards that were canceled		0.1			0.1
Ending balance, shares at Dec. 31, 2016									17,651,461
Ending balance at Dec. 31, 2016							(36.7)	$ 804.7	$ 0.2	$ 1,047.4	$ 75.2	$ (281.4)	$ (36.7)
Stockholders' Equity [Roll Forward]
Net income		45.4			45.4
Issuance of non-vested shares to employees			11,817
Issuance of common shares to non-employee directors		0.2		0.2
Issuance of common shares to directors, shares			2,282
Issuance of common shares to employees upon vesting of restricted stock units and performance shares, shares			103,652
Issuance of common shares to employees upon vesting of restricted stock units and performance shares				0.0
Cancellation of employee non-vested shares, shares			(451)
Cancellation of shares to cover employees’ tax withholdings upon vesting of non-vested shares, shares			(56,495)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		$ (4.5)		(4.5)
Repurchase of common stock, shares		(938,680)	(938,680)
Repurchase of common stock		$ (77.8)				(77.8)
Cancellation of treasury stock				(0.2)	(0.4)	0.6
Cash dividends on common stock	[1]	(35.0)			(35.0)
Amortization of unearned equity compensation		$ 13.0		13.0
Ending balance, shares at Dec. 31, 2017		16,773,586	16,773,586
Ending balance at Dec. 31, 2017		$ 746.3	$ 0.2	1,055.9	85.5	(358.6)	(36.7)
Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment		0.3			0.3
Net income		91.7			91.7
Other comprehensive income (loss), net of tax		(11.7)					(11.7)
Issuance of non-vested shares to employees			9,009
Issuance of common shares to non-employee directors		0.2		0.2
Issuance of common shares to directors, shares			1,954
Issuance of common shares to employees upon vesting of restricted stock units and performance shares, shares			135,400
Cancellation of shares to cover employees’ tax withholdings upon vesting of non-vested shares, shares			(68,195)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		$ (6.9)		(6.9)
Repurchase of common stock, shares		(617,151)	(617,151)
Repurchase of common stock		$ (61.9)				(61.9)
Cash dividends on common stock	[1]	(37.7)			(37.7)
Amortization of unearned equity compensation		$ 10.1		10.1
Ending balance, shares at Dec. 31, 2018		16,234,603	16,234,603
Ending balance at Dec. 31, 2018		$ 740.4	$ 0.2	$ 1,059.3	$ 150.2	$ (420.5)	$ (48.8)

[1] Dividends declared per common share were $2.20, $2.00 and $1.80 during 2018, 2017 and 2016, respectively.