Stockholders' Equity (Details 2) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2011
Summary of stock option activity
Number of Shares, Outstanding, Beginning Balance	5,700
Weighted Average Exercise Price, Outstanding, Beginning Balance	$ 46.56
Number of Shares, Granted	1,003
Number of Shares, Exercised	(873)
Number of Shares, Cancelled	(38)
Weighted Average Exercise Price, Granted	$ 65.38
Weighted Average Exercise Price, Exercised	$ 43.83
Weighted Average Exercise Price, Cancelled	$ 49.13
Number of Shares, Outstanding, Ending Balance	5,792
Weighted Average Exercise Price, Outstanding, Ending Balance	$ 50.21
Weighted Average Remaining Contractual Term, Outstanding, Ending Balance	4.4
Aggregate Intrinsic Value, Outstanding, Ending Balance	$ 111,156
Number of shares, Exercisable, Ending Balance	3,542
Weighted Average Exercise Price, Exercisable, Ending Balance	$ 47.65
Weighted Average Remaining Contractual Term, Exercisable, Ending Balance	3.5
Aggregate Intrinsic Value, Exercisable, Ending Balance	$ 76,209