Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Stock Options [Member]	Dec. 31, 2013 Stock Options [Member]
Number of Shares, Outstanding Beginning of Period	1,175,657
Number of options granted	0
Number of Shares, Exercised	(352,966)
Number of Shares, Canceled	0
Number of Shares, Outstanding Ending of Period	822,691
Number of Shares, Exercisable	611,372
Number of Shares, Vested and expected to vest	793,255
Weighted-Average Exercise Price, Outstanding Beginning of Period	$ 21.21
Weighted-Average Exercise Price, Granted	$ 0.00
Weighted-Average Exercise Price, Exercised	$ 14.46
Weighted-Average Exercise Price, Canceled	$ 0.00
Weighted-Average Exercise Price, Outstanding Ending of Period	$ 24.10
Weighted-Average Exercise Price, Exercisable	$ 23.33
Weighted-Average Exercise Price, Vested and expected to vest	$ 23.97
Weighted-Average Remaining Contractual Term, Outstanding (in years)	4 years 8 months 1 day
Weighted-Average Remaining Contractual Term, Exercisable (in years)	3 years 11 months 9 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)	4 years 6 months 29 days
Aggregate Intrinsic Value, Outstanding	$ 21,344,914
Aggregate Intrinsic Value, Exercisable	16,335,927
Aggregate Intrinsic Value, Vested and expected to vest	20,685,031
Aggregate intrinsic values of options exercised	12,300,000	1,400,000
Unrecognized compensation cost related to non-vested awards granted			$ 1,500,000	$ 2,000,000
Weighted-average period to recognize compensation cost (in years)			1 year 9 months 15 days