Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 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	(268,793)
Number of Shares, Canceled	(20,600)
Number of Shares, Outstanding Ending of Period	1,476,068
Number of Shares, Exercisable	1,126,109
Number of Shares, Vested and expected to vest	1,411,380
Weighted-Average Exercise Price, Outstanding Beginning of Period	$ 22.08
Weighted-Average Exercise Price, Granted	$ 0.00
Weighted-Average Exercise Price, Exercised	$ 24.27
Weighted-Average Exercise Price, Canceled	$ 21.79
Weighted-Average Exercise Price, Outstanding Ending of Period	$ 21.69
Weighted-Average Exercise Price, Exercisable	$ 21.16
Weighted-Average Exercise Price, Vested and expected to vest	$ 21.53
Weighted-Average Remaining Contractual Term, Outstanding (in years)	4 years 6 months 26 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)	3 years 9 months 29 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)	4 years 5 months 9 days
Aggregate Intrinsic Value, Outstanding	$ 30,731,407
Aggregate Intrinsic Value, Exercisable	24,039,530
Aggregate Intrinsic Value, Vested and expected to vest	29,614,301
Aggregate intrinsic values of options exercised	4,000,000	3,200,000
Unrecognized compensation cost related to non-vested awards granted			$ 3,300,000	$ 5,000,000
Weighted-average period to recognize compensation cost (in years)			1 year 11 months 9 days