Stock Options And Employee Stock Purchase Plan (Stock Options) (Details) (USD $)	6 Months Ended
	Jun. 30, 2012 Y	Jun. 30, 2011	Jun. 30, 2012 Stock Options [Member]	Dec. 31, 2011 Stock Options [Member]
Number of Shares, Outstanding Beginning of Period	2,087,695
Number of options granted	57,000
Number of Shares, Exercised	(225,410)
Number of Shares, Canceled	(16,000)
Number of Shares, Outstanding Ending of Period	1,903,285
Number of Shares, Exercisable	1,212,489
Number of Shares, Vested and expected to vest	1,803,435
Weighted-Average Exercise Price, Outstanding Beginning of Period	$ 20.99
Weighted-Average Exercise Price, Granted	$ 27.04
Weighted-Average Exercise Price, Exercised	$ 13.27
Weighted-Average Exercise Price, Canceled	$ 33.54
Weighted-Average Exercise Price, Outstanding Ending of Period	$ 21.98
Weighted-Average Exercise Price, Exercisable	$ 21.45
Weighted-Average Exercise Price, Vested and expected to vest	$ 21.82
Weighted-Average Remaining Contractual Term, Outstanding (in years)	5 years 7 months 6 days
Weighted-Average Remaining Contractual Term, Exercisable (in years)	4 years 6 months
Weighted-Average Remaining Contractual Term, Vested and expected to vest (in years)	5 years 4 months 24 days
Aggregate Intrinsic Value, Outstanding	$ 11,001,387
Aggregate Intrinsic Value, Exercisable	7,867,462
Aggregate Intrinsic Value, Vested and expected to vest	10,701,380
Expiration period of options granted (in years)	10
Aggregate intrinsic values of options exercised	3,200,000	6,200,000
Unrecognized compensation cost related to non-vested awards granted			$ 6,800,000	$ 9,000,000
Weighted-average period to recognize compensation cost (in years)			2 years 4 months 24 days