Revenue from Contracts with Customers (Impact of ASC 606 on Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Jun. 29, 2019	Mar. 30, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 295,486		$ 314,777	$ 920,626	$ 929,303
Cost of revenue	82,705		81,633	239,961	248,376
Gross margin	212,781		233,144	680,665	680,927
Sales and marketing	108,202		107,801	316,142	305,566
Research and development	60,590		61,221	182,774	187,390
General and administrative	28,773		33,098	102,008	101,487
Amortization of acquired intangible assets	5,920		7,850	17,786	23,566
Restructuring and other charges, net	(9)		1,627	45,464	1,846
Total operating expenses	203,476		211,597	664,174	619,855
Operating income	9,305		21,547	16,491	61,072
Interest expense	(10,816)		(10,646)	(32,475)	(31,072)
Other income (expense), net	1,026		(930)	2,501	(2,013)
Income (loss) before income taxes	(485)		9,971	(13,483)	27,987
Provision (benefit) for income taxes	14,273		(7,026)	23,803	(10,809)
Net income (loss)	(14,758)		16,997	(37,286)	38,796
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	322,410		314,777	976,666	929,303
Cost of revenue	81,233			234,396
Gross margin	241,177			742,270
Sales and marketing	113,533			330,258
Research and development	60,590			182,774
General and administrative	28,773			102,008
Amortization of acquired intangible assets	5,920			17,786
Restructuring and other charges, net	(9)			45,464
Total operating expenses	208,807			678,290
Operating income	32,370			63,980
Interest expense	(10,816)			(32,475)
Other income (expense), net	736			2,349
Income (loss) before income taxes	22,290			33,854
Provision (benefit) for income taxes	10,585			14,931
Net income (loss)	11,705			18,923
Software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	253,405		273,619	796,169	801,262
Cost of revenue	47,092		46,273	136,601	139,078
Software | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	281,939		273,619	858,228	801,262
Cost of revenue	46,604			134,803
Support and cloud services
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	190,487		137,051	566,053	424,671
Cost of revenue	33,785		34,291	97,856	103,128
Support and cloud services | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	118,719			364,972
Cost of revenue	33,606			97,213
License
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	62,918		136,568	230,116	376,591
Cost of revenue	13,307		11,982	38,745	35,950
License | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	163,220	$ 28,700		493,256
Cost of revenue	12,998			37,590
Professional services
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	42,081		41,158	124,457	128,041
Cost of revenue	35,613		35,360	103,360	109,298
Professional services | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	40,471		$ 41,158	118,438	$ 128,041
Cost of revenue	34,629			99,593
Accounting Standards Update 2014-09 | License
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	49,800			173,100
Revenue On New And Renewal Bookings	$ 51,700			$ 115,100