Consolidated Statements Of Shareholders' Equity (USD $) In Millions, except Share data	Common Stock [Member]	Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance at Dec. 31, 2009	$ 0.3	$ 24.4	$ 474.4	$ (0.9)	$ 498.2
Balance, shares at Dec. 31, 2009	31,038,217
Net income			170.1		170.1
Other comprehensive income (loss)				0.8	0.8
Stock-based compensation		4.1			4.1
Restricted stock awards, net of forfeitures, shares	12,565
Repurchase of common stock		(1.0)	(201.2)		(202.2)	[1]
Repurchase of common stock, shares	(4,047,311)				(4,047,311)
Stock options exercised		2.9			2.9
Stock options exercised, shares	300,475
Tax benefits from stock-based compensation plans		0.6			0.6
Balance at Dec. 31, 2010	0.3	31.0	443.3	(0.1)	474.5
Balance, shares at Dec. 31, 2010	27,303,946
Net income			188.0		188.0
Other comprehensive income (loss)				0.1	0.1
Stock-based compensation		1.9			1.9
Restricted stock awards, net of forfeitures, shares	(842)
Repurchase of common stock		(0.4)	(130.4)		(130.8)	[1]
Repurchase of common stock, shares	(1,979,444)				(1,979,444)
Stock options exercised		2.9			2.9
Stock options exercised, shares	300,024
Tax benefits from stock-based compensation plans		3.4			3.4
Balance at Dec. 31, 2011	0.3	38.8	500.9		540.0	[2]
Balance, shares at Dec. 31, 2011	25,623,684				25,623,684
Net income			219.7		219.7
Other comprehensive income (loss)				(0.1)	(0.1)
Stock-based compensation		12.2			12.2
Restricted stock awards, net of forfeitures, shares	195,679
Repurchase of common stock	(0.1)	(0.2)	(152.2)		(152.5)	[1]
Repurchase of common stock, shares	(1,740,372)				(1,740,372)
Stock options exercised		0.6			0.6
Stock options exercised, shares	35,905
Tax benefits from stock-based compensation plans		2.0			2.0
Balance at Dec. 31, 2012	$ 0.2	$ 53.4	$ 568.4	$ (0.1)	$ 621.9	[2]
Balance, shares at Dec. 31, 2012	24,114,896				24,114,896

[1] Tender Offer amounts include offering costs of $0.3 million, $0.2 million, and $0.3 million for 2012, 2011 and 2010, respectively.

[2] No dividends were paid during the periods presented.