Stockholders' Equity (Stock Options Vested, or Expected to Vest and Exercisable) (Details) - Stock Options [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, Number of options	5,623	5,766	5,387
Options outstanding, Weighted-Average Exercise Price	$ 60.50	$ 59.97	$ 53.73
Options outstanding, Weighted-Average Remaining Life in Years	6 years
Options outstanding, Aggregate Intrinsic Value	$ 56,006
Options vested and exercisable, Number of options	3,755
Options vested and exercisable, Weighted-Average Exercise Price Per Share	$ 47.67
Options vested and exercisable, Weighted-Average Remaining Life in Years	4 years 9 months 18 days
Options vested and exercisable, Aggregate Intrinsic Value	$ 56,006
Options vested and expected to vest, Number of options	5,515
Options vested and expected to vest, Weighted-Average Exercise Price Per Share	$ 59.92
Options vested and expected to vest, Weighted-Average Remaining Life in Years	5 years 10 months 24 days
Options vested and expected to vest, Aggregate Intrinsic Value	$ 56,006