Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) (USD $)	9 Months Ended
	Sep. 30, 2011 years	Sep. 30, 2010	Sep. 30, 2011 Stock Options [Member]	Dec. 31, 2010 Stock Options [Member]
Number of Shares, Outstanding Beginning of Period	3,794,394
Number of options granted	130,819
Number of Shares, Exercised	(1,781,950)
Number of Shares, Canceled	(41,140)
Number of Shares, Outstanding Ending of Period	2,102,123
Number of Shares, Exercisable	1,179,263
Number of Shares, Vested and expected to vest	1,959,636
Weighted-Average Exercise Price, Outstanding Beginning of Period	$ 14.40
Weighted-Average Exercise Price, Granted	$ 29.01
Weighted-Average Exercise Price, Exercised	$ 8.04
Weighted-Average Exercise Price, Canceled	$ 24.69
Weighted-Average Exercise Price, Outstanding Ending of Period	$ 20.50
Weighted-Average Exercise Price, Exercisable	$ 19.23
Weighted-Average Exercise Price, Vested and expected to vest	$ 20.34
Weighted-Average Remaining Contractual Term, Outstanding (in years)	5.8
Weighted-Average Remaining Contractual Term, Exercisable (in years)	4.3
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)	5.6
Aggregate Intrinsic Value, Outstanding	$ 15,655,942
Aggregate Intrinsic Value, Exercisable	10,587,334
Aggregate Intrinsic Value, Vested and expected to vest	14,970,305
Expiration period of options granted (in years)	10
Weighted-average grant date fair value of options granted	$ 13.12	$ 10.94
Aggregate intrinsic values of options exercised	38,900,000	10,000,000
Unrecognized compensation cost related to non-vested awards granted			$ 10,200,000	$ 12,900,000
Weighted-average period to recognize compensation cost (in years)			2.6