Stockholders' Equity (Stock Options Vested, Or Expected to Vest and Are Exercisable) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Stock-Based Compensation
Options outstanding, Number of options	5,331	4,792	4,944
Options outstanding, Weighted-Average Exercise Price	$ 39.43	$ 35.35	$ 35.35
Options outstanding, Weighted-Average Remaining Life in Years	6 years 4 months 24 days
Options outstanding, Aggregate Intrinsic Value	$ 151,901
Options vested and exercisable, Number of options	3,254
Options vested and exercisable, Weighted-Average Exercise Price Per Share	$ 32.80
Options vested and exercisable, Weighted-Average Remaining Life in Years	5 years
Options vested and exercisable, Aggregate Intrinsic Value	$ 114,271
Options vested and expected to vest, Number of options	5,224
Options vested and expected to vest, Weighted-Average Exercise Price Per Share	$ 39.18
Options vested and to expected vest, Weighted-Average Remaining Life in Years	6 years 3 months 18 days
Options vested and expected to vest, Aggregate Intrinsic Value	$ 150,155