Revenue from Contracts with Customers (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 1,255,631	$ 1,241,824	$ 1,164,039
Subscription license
Disaggregation of Revenue [Line Items]
Revenue	253,698
Subscription support & cloud services
Disaggregation of Revenue [Line Items]
Revenue	348,452
Subscription Services
Disaggregation of Revenue [Line Items]
Revenue	602,150
Perpetual support
Disaggregation of Revenue [Line Items]
Revenue	415,248
Recurring Services
Disaggregation of Revenue [Line Items]
Revenue	1,017,398
Perpetual license
Disaggregation of Revenue [Line Items]
Revenue	70,702
Software
Disaggregation of Revenue [Line Items]
Revenue	1,088,100	1,088,487	987,316
Professional services
Disaggregation of Revenue [Line Items]
Revenue	167,531	153,337	176,723
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,311,494	1,241,824	1,164,039
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Subscription Services
Disaggregation of Revenue [Line Items]
Revenue	667,597	482,027	279,246
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Perpetual support
Disaggregation of Revenue [Line Items]
Revenue	411,030	496,826	574,680
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Recurring Services
Disaggregation of Revenue [Line Items]
Revenue	1,078,627	978,853	853,926
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Perpetual license
Disaggregation of Revenue [Line Items]
Revenue	72,191	109,634	133,390
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Software
Disaggregation of Revenue [Line Items]
Revenue	1,150,818	1,088,487	987,316
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Professional services
Disaggregation of Revenue [Line Items]
Revenue	$ 160,676	$ 153,337	$ 176,723