Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Stock Options [Member]	Dec. 31, 2012 Stock Options [Member]
Number of Shares, Outstanding Beginning of Period	1,765,461
Number of options granted	0
Number of Shares, Exercised	(562,173)
Number of Shares, Canceled	(20,600)
Number of Shares, Outstanding Ending of Period	1,182,688
Number of Shares, Exercisable	836,229
Number of Shares, Vested and expected to vest	1,127,602
Weighted-Average Exercise Price, Outstanding Beginning of Period	$ 22.08
Weighted-Average Exercise Price, Granted	$ 0.00
Weighted-Average Exercise Price, Exercised	$ 24.04
Weighted-Average Exercise Price, Canceled	$ 21.79
Weighted-Average Exercise Price, Outstanding Ending of Period	$ 21.16
Weighted-Average Exercise Price, Exercisable	$ 20.25
Weighted-Average Exercise Price, Vested and expected to vest	$ 20.94
Weighted-Average Remaining Contractual Term, Outstanding (in years)	4 years 3 months 11 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)	3 years 3 months 11 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)	4 years 1 month 17 days
Aggregate Intrinsic Value, Outstanding	$ 33,542,013
Aggregate Intrinsic Value, Exercisable	24,476,289
Aggregate Intrinsic Value, Vested and expected to vest	32,231,627
Aggregate intrinsic values of options exercised	11,600,000	4,000,000
Unrecognized compensation cost related to non-vested awards granted			$ 2,600,000	$ 5,000,000
Weighted-average period to recognize compensation cost (in years)			1 year 8 months 1 day