Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payments for repurchases of common stock		$ 24,004,000
Exercise prices of stock options outstanding	$ 44.48		$ 39.58
Total unrecognized compensation cost related to non-vested stock-based compensation arrangements	$ 14,234,000
Unrecognized compensation cost is expected to be recognized over a weighted-average period	2 years 4 months 24 days
Forfeiture rate, Board of Directors	0.00%
Forfeiture rate, non-Board of Directors	9.00%
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation award conditionally awarded date		Oct. 03, 2016
Stock-based compensation award conditionally awarded date approved		Jan. 25, 2017
Vested contractual term, in years	10 years
Vesting rate	25.00%
Employee stock-based compensation expense	$ 12,423,000	$ 1,261,000
2017 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock shares authorized for grants	2,000
Employee stock-based compensation expense		0
2016 Authorization [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized repurchase amount	$ 500,000,000
Payments for repurchases of common stock	$ 0
Repurchase period in years	3 years
10b5-1 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payments for repurchases of common stock		$ 24,004,000
Purchases of treasury stock, number of shares		350