Statements of Consolidated Stockholders' Equity (Unaudited) - 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		$ 10.1			$ 10.5	$ 0.0	$ (0.4)
Adjusted balance		$ 756.4	$ 0.2	$ 1,055.9	96.0	(358.6)	(37.1)
Common Stock, Dividends, Per Share, Declared		$ 0.55
Beginning balance (shares) at Dec. 31, 2017			16,773,586
Beginning balance at Dec. 31, 2017		$ 746.3	$ 0.2	1,055.9	85.5	(358.6)	(36.7)
Stockholders' Equity [Roll Forward]
Net income		25.7			25.7
Other comprehensive income (loss), net of tax		(8.3)					(8.3)
Issuance of common shares to employees upon vesting of restricted stock units and performance shares (shares)			135,134
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(68,029)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(6.9)		(6.9)
Repurchase of common stock (shares)	[1]		(58,155)
Repurchase of common stock1	[1]	(6.1)				(6.1)
Cash dividends on common stock and restricted shares and dividend equivalents on restricted stock units and performance shares2	[2]	(10.0)			(10.0)
Amortization of unearned equity compensation		2.8		2.8
Ending balance (shares) at Mar. 31, 2018			16,782,536
Ending balance at Mar. 31, 2018		753.6	$ 0.2	1,051.8	111.7	(364.7)	(45.4)
Beginning balance (shares) at Dec. 31, 2017			16,773,586
Beginning balance at Dec. 31, 2017		746.3	$ 0.2	1,055.9	85.5	(358.6)	(36.7)
Stockholders' Equity [Roll Forward]
Net income		68.1
Ending balance (shares) at Sep. 30, 2018			16,547,237
Ending balance at Sep. 30, 2018		$ 762.5	$ 0.2	1,057.4	135.6	(390.9)	(39.8)
Common Stock, Dividends, Per Share, Declared		$ 0.55
Beginning balance (shares) at Mar. 31, 2018			16,782,536
Beginning balance at Mar. 31, 2018		$ 753.6	$ 0.2	1,051.8	111.7	(364.7)	(45.4)
Stockholders' Equity [Roll Forward]
Net income		20.7			20.7
Other comprehensive income (loss), net of tax		6.4					6.4
Issuance of non-vested shares to non-employee directors (shares)			9,009
Issuance of common shares to non-employee directors (shares)			1,954
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)			82
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(95)
Repurchase of common stock (shares)	[1]		(127,545)
Repurchase of common stock1	[1]	(13.3)				(13.3)
Cash dividends on common stock and restricted shares and dividend equivalents on restricted stock units and performance shares2	[2]	(9.3)			(9.3)
Amortization of unearned equity compensation		2.7		2.7
Ending balance (shares) at Jun. 30, 2018			16,665,941
Ending balance at Jun. 30, 2018		$ 761.0	$ 0.2	1,054.7	123.1	(378.0)	(39.0)
Common Stock, Dividends, Per Share, Declared		$ 0.55
Stockholders' Equity [Roll Forward]
Net income		$ 21.7			21.7
Other comprehensive income (loss), net of tax		(0.8)					(0.8)
Issuance of common shares to employees upon vesting of restricted stock units and performance shares (shares)			78
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(42)
Repurchase of common stock (shares)	[1]		(118,740)
Repurchase of common stock1	[1]	(12.9)				(12.9)
Cash dividends on common stock and restricted shares and dividend equivalents on restricted stock units and performance shares2	[2]	(9.2)			(9.2)
Amortization of unearned equity compensation		2.7		2.7
Ending balance (shares) at Sep. 30, 2018			16,547,237
Ending balance at Sep. 30, 2018		$ 762.5	$ 0.2	1,057.4	135.6	(390.9)	(39.8)
Common Stock, Dividends, Per Share, Declared		$ 0.60
Beginning balance (shares) at Dec. 31, 2018		16,234,603	16,234,603
Beginning balance at Dec. 31, 2018		$ 740.4	$ 0.2	1,059.3	150.2	(420.5)	(48.8)
Stockholders' Equity [Roll Forward]
Net income		28.0			28.0
Other comprehensive income (loss), net of tax		9.7					9.7
Issuance of common shares to employees upon vesting of restricted stock units and performance shares (shares)			122,309
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(46,388)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(5.0)		(5.0)
Repurchase of common stock (shares)	[3]		(175,977)
Repurchase of common stock1	[3]	(17.4)				(17.4)
Cash dividends on common stock and restricted shares and dividend equivalents on restricted stock units and performance shares2	[4]	(10.2)			(10.2)
Amortization of unearned equity compensation		2.4		2.4
Ending balance (shares) at Mar. 31, 2019			16,134,547
Ending balance at Mar. 31, 2019		$ 747.9	$ 0.2	1,056.7	168.0	(437.9)	(39.1)
Beginning balance (shares) at Dec. 31, 2018		16,234,603	16,234,603
Beginning balance at Dec. 31, 2018		$ 740.4	$ 0.2	1,059.3	150.2	(420.5)	(48.8)
Stockholders' Equity [Roll Forward]
Net income		$ 72.6
Ending balance (shares) at Sep. 30, 2019		15,900,956	15,900,956
Ending balance at Sep. 30, 2019		$ 751.4	$ 0.2	1,061.5	193.0	(460.1)	(43.2)
Common Stock, Dividends, Per Share, Declared		$ 0.60
Beginning balance (shares) at Mar. 31, 2019			16,134,547
Beginning balance at Mar. 31, 2019		$ 747.9	$ 0.2	1,056.7	168.0	(437.9)	(39.1)
Stockholders' Equity [Roll Forward]
Net income		19.2			19.2
Other comprehensive income (loss), net of tax		(3.2)					(3.2)
Issuance of non-vested shares to non-employee directors (shares)			11,850
Issuance of common shares to non-employee directors (shares)			2,850
Issuance of common shares to non-employee directors		0.3		0.3
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares (shares)			(12,395)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(1.2)		(1.2)
Repurchase of common stock (shares)	[3]		(108,177)
Repurchase of common stock1	[3]	(10.2)				(10.2)
Cash dividends on common stock and restricted shares and dividend equivalents on restricted stock units and performance shares2	[4]	(9.9)			(9.9)
Amortization of unearned equity compensation		3.4		3.4
Ending balance (shares) at Jun. 30, 2019			16,028,675
Ending balance at Jun. 30, 2019		746.3	$ 0.2	1,059.2	177.3	(448.1)	(42.3)
Stockholders' Equity [Roll Forward]
Net income		25.4			25.4
Other comprehensive income (loss), net of tax		(0.9)					(0.9)
Issuance of non-vested shares to non-employee directors (shares)			896
Repurchase of common stock (shares)	[3]		(128,615)
Repurchase of common stock1	[3]	(12.0)				(12.0)
Cash dividends on common stock and restricted shares and dividend equivalents on restricted stock units and performance shares2	[4]	(9.7)			(9.7)
Amortization of unearned equity compensation		$ 2.3		2.3
Ending balance (shares) at Sep. 30, 2019		15,900,956	15,900,956
Ending balance at Sep. 30, 2019		$ 751.4	$ 0.2	$ 1,061.5	$ 193.0	$ (460.1)	$ (43.2)

[1] Weighted-average repurchase price (dollars per share) for the quarters ended March 31, 2018, June 30, 2018 and September 30, 2018 was $104.50, $104.74 and $108.07, respectively.

[2] Dividends declared per common share were $0.55 during each of the quarters ended March 31, 2018, June 30, 2018 and September 30, 2018.

[3] Weighted-average repurchase price (dollars per share) for the quarters ended March 31, 2019, June 30, 2019 and September 30, 2019 was $98.55, $95.00 and $92.95, respectively. At September 30, 2019, $108.9 million remained available to repurchase our common shares pursuant to the stock repurchase program.

[4] Dividends declared per common share were $0.60 during each of the quarters ended March 31, 2019, June 30, 2019 and September 30, 2019.