Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payments for repurchases of common stock	$ 0	$ 71,751	$ 125,541
Exercise prices of stock options outstanding	$ 45.42	$ 39.58
Employee stock-based compensation expense	$ 18,229	$ 17,282	15,122
Total unrecognized compensation cost related to non-vested stock-based compensation arrangements	$ 9,887
Unrecognized compensation cost is expected to be recognized over a weighted-average period	1 year 9 months 18 days
Forfeiture rate, Board of Directors	0.00%
Forfeiture rate, non-Board of Directors	9.00%
Shares granted, Number of Shares	10,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested contractual term, in years	10 years
Vesting rate	25.00%
Vesting period, in years	4 years
Restricted Stock Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate	50.00%
Vesting period, in years	2 years
2017 Authorization [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized repurchase amount	$ 500,000
Payments for repurchases of common stock		$ 71,197
Repurchase period in years	3 years
Purchases of treasury stock, number of shares	0	1,027,000
Number of shares available for future grants	1,300
Goldman Sachs Accelerated Share Repurchase Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized repurchase amount			125,000
Purchases of treasury stock			$ 125,000
Purchases of treasury stock, number of shares			2,635,000
10b5-1 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchases of treasury stock, number of shares		491,000
10b-18 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchases of treasury stock, number of shares		536,000
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise prices of stock options outstanding	$ 18.67
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise prices of stock options outstanding	$ 78.97