Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Number of Shares, Outstanding Beginning of Period	2,087,695	3,794,394	4,480,591
Number of options granted	67,000	163,319	167,967
Number of Shares, Exercised	357,234	1,820,678	816,552
Number of Shares, Canceled	32,000	49,340	37,612
Number of Shares, Outstanding Ending of Period	1,765,461	2,087,695	3,794,394
Number of Shares, Exercisable	1,132,365
Number of Shares, Vested and expected to vest	1,664,406
Weighted-Average Exercise Price, Outstanding Beginning of Period	$ 20.99	$ 14.40	$ 13.17
Weighted-Average Exercise Price, Granted	$ 27.26	$ 29.42	$ 23.13
Weighted-Average Exercise Price, Exercised	$ 15.81	$ 7.92	$ 9.18
Weighted-Average Exercise Price, Canceled	$ 31.34	$ 24.76	$ 20.26
Weighted-Average Exercise Price, Outstanding Ending of Period	$ 22.08	$ 20.99	$ 14.40
Weighted-Average Exercise Price, Vested and expected to vest	$ 21.95
Weighted-Average Remaining Contractual Term, Outstanding (in years)	5 years 1 month 6 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)	4 years
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)	4 years 10 months 24 days
Aggregate Intrinsic Value, Outstanding	$ 15,684,163
Aggregate Intrinsic Value, Exercisable	10,451,569
Aggregate Intrinsic Value, Vested and expected to vest	15,042,947
Aggregate intrinsic values of options exercised	4,500,000	41,400,000	13,200,000
Stock Options [Member]
Unrecognized compensation cost related to non-vested awards granted	$ 5,000,000
Weighted-average period to recognize compensation cost (in years)	2 years 0 months 11 days