Stockholders' Equity (Details 5) (USD $)	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Intrinsic value
Stock price (in dollars per share)	$ 50.21
Options
Fair value assumptions
Expected volatility (as a percent)	60.40%
Expected volatility, minimum (as a percent)		63.90%	66.50%
Expected volatility, maximum (as a percent)		64.80%	69.40%
Risk-free interest rate (as a percent)	0.60%
Risk free interest rate, minimum (as a percent)		0.30%	0.30%
Risk free interest rate, maximum (as a percent)		1.70%	1.80%
Expected forfeiture rate (as a percent)	19.00%	18.40%	19.60%
Intrinsic value
Intrinsic value of outstanding shares	$ 60,946,000
Intrinsic value of exercisable options	35,448,000
Weighted average grant date fair value
Weighted average grant date fair value of options granted (in dollars per share)	$ 34.42	$ 15.21	$ 4.02
Intrinsic value of options exercised	$ 26,911,000	$ 43,706,000	$ 3,342,000