Stockholders' Equity (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended		9 Months Ended			9 Months Ended		12 Months Ended		12 Months Ended			0 Months Ended				0 Months Ended
	Jun. 07, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Incentive Stock Option [Member]	Dec. 31, 1998 Nineteen Ninety Eight Plan [Member] Incentive Stock Option [Member] Maximum [Member]	Dec. 31, 2000 Two Thousand Plan [Member] Incentive Stock Option [Member]	Dec. 31, 2000 Nineteen Ninety Eight and Two Thousand Plan [Member] Incentive Stock Option [Member]	Dec. 31, 2009 Two Thousand Nine Plan [Member] Incentive Stock Option [Member]	Sep. 30, 2013 Two Thousand Nine Plan [Member] Incentive Stock Option [Member]	Jun. 07, 2012 Two Thousand Nine Plan [Member] Incentive Stock Option [Member]	Apr. 30, 2010 Two Thousand Employee Stock Purchase Plan [Member]	Mar. 31, 2000 Two Thousand Employee Stock Purchase Plan [Member]	Sep. 30, 2013 Employee Stock Purchase Plan, 2010 [Member]	Jun. 30, 2010 Employee Stock Purchase Plan, 2010 [Member]	Jun. 07, 2012 2009 Plan [Member] Two Thousand Nine Plan [Member] Incentive Stock Option [Member]
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common stock, shares issued (in shares)		54,123,328		54,123,328		55,948,924
Common stock, shares outstanding (in shares)		54,123,328		54,123,328		55,948,924
Common stock, par value (in dollars per share)		$ 0.001		$ 0.001		$ 0.001
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred stock, shares issued (in shares)		0		0		0
Preferred stock, shares outstanding (in shares)		0		0		0
Preferred stock, par value (in dollars per share)		$ 0.001		$ 0.001		$ 0.001
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock available for issuance, expiration date														Apr. 01, 2010
Weighted average fair value of stock options granted		$ 4.82	$ 8.78	$ 5.25	$ 8.23
Shares of common stock available for issuance								5,850,000		10,000,000		15,000,000	23,817,744		450,000	726,000	1,000,000
Increase in number of shares of common stock available for issuance									4,150,000		6,000,000							4,250,000
Stock option term	10 years
Unrecognized compensation cost related to nonvested share-based compensation arrangements							$ 33.4
Weighted average recognition period of unrecognized compensation cost							2 years
Total value of stock options exercised				2.1
Total intrinsic value of options exercisable		11.9		11.9
Total intrinsic value of nonvested options		0.5		0.5
Total intrinsic value of all outstanding options		$ 12.5		$ 12.5