Consolidated Statements Of Shareholders' Equity (USD $) In Millions, except Share data	Total		Common Stock [Member]	Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at at Dec. 31, 2011	$ 540.0		$ 0.3	$ 38.8	$ 500.9	$ 0
Balance, shares at at Dec. 31, 2011			25,623,684
Net income	219.7		0	0	219.7	0
Other comprehensive income (loss)	(0.1)		0	0	0	(0.1)
Stock-based compensation	12.2		0	12.2	0	0
Restricted stock awards, net of forfeitures, shares			195,679
Repurchase of common stock	(152.5)		(0.1)	(0.2)	(152.2)	0
Repurchase of common stock, shares	(1,740,372)		(1,740,372)
Stock options exercised	0.6		0	0.6	0	0
Stock options exercised, shares			35,905
Tax benefits from stock-based compensation plans	2.0		0	2.0	0	0
Balance at at Dec. 31, 2012	621.9		0.2	53.4	568.4	(0.1)
Balance, shares at at Dec. 31, 2012			24,114,896
Net income	253.1		0	0	253.1	0
Other comprehensive income (loss)	(0.1)		0	0	0	(0.1)
Stock-based compensation	8.5		0	8.5	0	0
Restricted stock awards, net of forfeitures, shares			8,349
Repurchase of common stock	(135.2)		0	(0.6)	(134.6)	0
Repurchase of common stock, shares	(1,216,015)		(1,216,015)
Restricted stock units converted to common stock, shares			848
Stock options exercised	0.6		0	0.6	0	0
Stock options exercised, shares			35,000
Tax benefits from stock-based compensation plans	1.3		0	1.3	0	0
Balance at at Dec. 31, 2013	750.1	[1]	0.2	63.2	686.9	(0.2)
Balance, shares at at Dec. 31, 2013	22,943,078		22,943,078
Net income	266.2		0	0	266.2	0
Other comprehensive income (loss)	0.1		0	0	0	0.1
Stock-based compensation	15.3		0	15.3	0	0
Restricted stock awards, net of forfeitures, shares			5,462
Repurchase of common stock	(343.7)		0	(4.0)	(339.7)	0
Repurchase of common stock, shares	(2,686,744)		(2,686,744)
Restricted stock units converted to common stock, shares			300,875
Stock options exercised	0.6		0	0.6	0	0
Stock options exercised, shares			35,000
Tax benefits from stock-based compensation plans	13.6		0	13.6	0	0
Balance at at Dec. 31, 2014	$ 702.2	[1]	$ 0.2	$ 88.7	$ 613.4	$ (0.1)
Balance, shares at at Dec. 31, 2014	20,597,671		20,597,671

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