Stockholders' Equity (Stock Options Vested, Or Expected to Vest and Are Exercisable) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2017	Sep. 30, 2017
Stock-Based Compensation
Options outstanding, Number of options	5,937	5,236
Options outstanding, Weighted-Average Exercise Price	$ 44.48	$ 39.58
Options outstanding, Weighted-Average Remaining Life in Years	6 years 2 months 12 days
Options outstanding, Aggregate Intrinsic Value	$ 192,105
Options vested and exercisable, Number of options	3,917
Options vested and exercisable, Weighted-Average Exercise Price Per Share	$ 35.64
Options vested and exercisable, Weighted-Average Remaining Life in Years	4 years 10 months 24 days
Options vested and exercisable, Aggregate Intrinsic Value	$ 160,206
Options vested and expected to vest, Number of options	5,823
Options vested and expected to vest, Weighted-Average Exercise Price Per Share	$ 44.07
Options vested and to expected vest, Weighted-Average Remaining Life in Years	6 years 1 month 6 days
Options vested and expected to vest, Aggregate Intrinsic Value	$ 190,725