Stockholders' Equity (Deficit) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Jan. 28, 2015	Apr. 23, 2014
Stockholders' Equity (Deficit)
Approved stock repurchase program, authorized amount			$ 450.0	$ 200.0
Repurchase of common stock (in shares)	1,339,499	7,731,428
Repurchase of common stock, amount	$ 55.1	$ 298.3
Remaining capacity under the stock repurchase program	$ 246.3			$ 25.4