Stock-Based Compensation Plans (Details) (USD $)			9 Months Ended				9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 Stock Options [Member]	Dec. 31, 2004 Stock Options [Member]	Dec. 31, 1997 Stock Options [Member]	May 09, 1994 Stock Options [Member]	Sep. 30, 2011 Restricted Stock [Member] Incentive Plan (2005) [Member]	May 10, 2005 Restricted Stock [Member] Incentive Plan (2005) [Member]	Sep. 30, 2011 Restricted Stock [Member] Incentive Plan (2010) [Member]	May 11, 2010 Restricted Stock [Member] Incentive Plan (2010) [Member]	Sep. 30, 2011 Employee Stock Purchase Plan [Member]	May 10, 2011 Employee Stock Purchase Plan [Member]	Sep. 30, 2011 Authorized Preferred Stock And Preferred Stock Purchase Rights Plan [Member]	Jan. 21, 2004 Authorized Preferred Stock And Preferred Stock Purchase Rights Plan [Member]
Number of shares reserved for issuance						13,668,750		4,050,000		3,362,304				750,000
Additional number of shares reserved for issuance (1997) (in shares)					10,631,250
Additional number of shares reserved for issuance (2004) (in shares)				1,125,000
Additional number of shares reserved for issuance (2010) (in shares)										3,000,000
Award vesting period, minimum (in years)			five				three		three
Award vesting period, mid (in years)							five		five
Award vesting period, maximum (in years)			ten				ten		ten
Number of shares available for grant									5,094,572
Additional number of shares available for grant												3,000,000
Percentage of the lower of the market related to purchase of common stock											85.00%
Maximum employee subscription rate											15.00%
Shares of common stock reserved for future employee purchases											3,921,240
Shares issued during the period, in shares											699,602
Weighted average grant date fair value, in dollar per share											$ 21.78
Preferred stock, shares authorized	5,000,000	5,000,000											5,000,000
Number of preferred shares declared for each share of common stock outstanding, in shares													1
Amount of Series A Participating Preferred Stock each right entitles its holder to purchase													one-thousandth
Exercise price of Series A Participating Preferred Stock Rights, in dollar per share													$ 200
Percentage of common stock before rights become exercisable													20.00%
Multiple of original exercise price for which holder is entitled to purchase (in number of times: 2x, 3x, etc.)													2
Redemption price of Series A Participating Preferred Stock													$ 0.01
Expiration date													May 10, 2014
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0