Stockholders' Equity (Details 4) (USD $)	0 Months Ended	1 Months Ended				3 Months Ended		9 Months Ended
	Oct. 31, 2011	Jul. 31, 2012	Jun. 30, 2012	May 31, 2012	Oct. 31, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Employee and non-employee stock option exercise data
Employee and non-employee stock options, Number of options exercised (in shares)						246,401	20,135	386,515	820,572
Cash received						$ 6,575,000	$ 224,000	$ 9,689,000	$ 23,948,000
Share Repurchase
Authorized aggregate repurchases of common stock			100,000,000		300,000,000
Period over which shares may be purchased under share repurchase program	2 years	1 year
Cost of shares repurchased				$ 88,000,000	$ 212,000,000	$ 42,900,000
Repurchased shares of common stock				2,000,000	4,700,000	788,288