Stockholders' Equity (Summary of Anti-Dilutive Options Excluded) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Summary of anti-dilutive options excluded
Options to purchase shares of common stock	740,879	1,683,333	588,785	1,695,000
Weighted-average exercise prices of anti-dilutive options	$ 32.17	$ 27.94	$ 31.37	$ 27.94