Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Loss
Shares outstanding, beginning (in shares) at Dec. 31, 2013		17,900,000
Shareholders' equity, beginning at Dec. 31, 2013	$ 704.8	$ 296.0	$ 408.8	$ 0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	46.4		46.4
Issuance of common stock (in shares)		400,000
Issuance of common stock	23.3	$ 23.3
Tax windfall from stock-based compensation	$ 7.7	$ 7.7
Repurchase of common stock (in shares)	(691,000)	(800,000)
Repurchase of common stock	$ (76.6)	$ (76.6)
Stock-based compensation	11.9	$ 11.9
Cash & restricted stock dividends	(17.3)		(17.3)
Foreign currency translation, net of tax	(0.1)			(0.1)
Change in pension benefits, net of tax	0.0
Shares outstanding, ending (in shares) at Dec. 31, 2014		17,500,000
Shareholders' equity, ending at Dec. 31, 2014	700.1	$ 262.3	437.9	(0.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	65.2		65.2
Issuance of common stock (in shares)		0
Issuance of common stock	3.5	$ 3.5
Tax windfall from stock-based compensation	5.5	$ 5.5
Repurchase of common stock (in shares)		(1,100,000)
Repurchase of common stock	(151.1)	$ (151.1)
Grants of restricted stock, net of forfeitures (in shares)		200,000
Grants of restricted stock, net of forfeitures	0.0	$ 0.0
Stock-based compensation	13.8	$ 13.8
Cash & restricted stock dividends	(19.3)		(19.3)
Foreign currency translation, net of tax	(0.5)			(0.5)
Change in pension benefits, net of tax	0.0
Shares outstanding, ending (in shares) at Dec. 31, 2015		16,600,000
Shareholders' equity, ending at Dec. 31, 2015	617.2	$ 134.0	483.8	(0.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	108.1		108.1
Issuance of common stock (in shares)		100,000
Issuance of common stock	$ 2.6	$ 2.6
Repurchase of common stock (in shares)	(211,790)	(300,000)
Repurchase of common stock	$ (39.0)	$ (39.0)
Grants of restricted stock, net of forfeitures (in shares)		100,000
Grants of restricted stock, net of forfeitures	0.0	$ 0.0
Stock-based compensation	18.9	$ 18.9
Cash & restricted stock dividends	(22.2)		(22.2)
Foreign currency translation, net of tax	0.2			0.2
Change in pension benefits, net of tax	(0.8)			(0.8)
Shares outstanding, ending (in shares) at Dec. 31, 2016		16,500,000
Shareholders' equity, ending at Dec. 31, 2016	$ 685.0	$ 116.5	$ 569.7	$ (1.2)