Equity Incentive Plan (Narrative) (Details)	1 Months Ended	12 Months Ended
	Jul. 31, 2005	Sep. 30, 2018 USD ($) shares / unit $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issuable per restricted stock unit | shares / unit		1
Share-based Compensation		$ 82,939,000	$ 76,708,000	$ 65,996,000
Total unrecognized compensation cost		$ 144,500,000
Weighted average remaining recognition period, in months		28 months
Common stock were available for grant under the 2000 plan | shares		2,300,000
Common stock were reserved for issuance | shares		3,300,000
ESPP maximum contribution percentage		10.00%
ESPP maximum contribution amount by employee		$ 25,000
ESPP purchase price as a % of stock price		85.00%
Vesting period	4 years
Option expiration period	10 years
Options outstanding and exercisable (in shares) | shares		0	0	0
Shares retained by company to cover tax withholdings | shares		700,000	500,000	600,000
Employee tax withholdings		$ 45,400,000	$ 26,700,000	$ 20,900,000
Restricted Shares and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share | $ / shares		$ 76.17	$ 51.27	$ 37.25
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation		$ 4,300,000	$ 3,200,000	$ 400,000
stock modification [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation			$ 10,000,000
TSR Units [Member] | Restricted Shares and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value per share | $ / shares		$ 4.35	$ 2.27