Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 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	(95,600)
Number of Shares, Canceled	(12,000)
Number of Shares, Outstanding Ending of Period	1,657,861
Number of Shares, Exercisable	1,171,505
Number of Shares, Vested and expected to vest	1,580,207
Weighted-Average Exercise Price, Outstanding Beginning of Period	$ 22.08
Weighted-Average Exercise Price, Granted	$ 0.00
Weighted-Average Exercise Price, Exercised	$ 21.18
Weighted-Average Exercise Price, Canceled	$ 25.09
Weighted-Average Exercise Price, Outstanding Ending of Period	$ 22.11
Weighted-Average Exercise Price, Exercisable	$ 21.58
Weighted-Average Exercise Price, Vested and expected to vest	$ 21.98
Weighted-Average Remaining Contractual Term, Outstanding (in years)	4 years 9 months 15 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)	3 years 10 months 24 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)	4 years 7 months 28 days
Aggregate Intrinsic Value, Outstanding	$ 28,342,082
Aggregate Intrinsic Value, Exercisable	20,651,647
Aggregate Intrinsic Value, Vested and expected to vest	27,221,158
Aggregate intrinsic values of options exercised	1,400,000	1,100,000
Unrecognized compensation cost related to non-vested awards granted			$ 4,100,000	$ 5,000,000
Weighted-average period to recognize compensation cost (in years)			1 year 11 months 9 days