Revenue from Contracts with Customers (Impact of ASC 606 on Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Mar. 30, 2019	Dec. 29, 2018	Mar. 31, 2018	Mar. 30, 2019	Mar. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	$ 290,451		$ 307,883	$ 625,140	$ 614,527
Cost of revenue	79,904		83,708	157,256	166,743
Gross margin	210,547		224,175	467,884	447,784
Sales and marketing	103,722		98,390	207,940	197,765
Research and development	61,402		62,197	122,184	126,169
General and administrative	35,371		33,369	73,235	68,389
Amortization of acquired intangible assets	5,930		7,895	11,866	15,716
Restructuring and other charges, net	26,980		114	45,473	219
Total operating expenses	233,405		201,965	460,698	408,258
Operating income (loss)	(22,858)		22,210	7,186	39,526
Interest expense	(11,383)		(10,379)	(21,659)	(20,426)
Other income (expense), net	821		(285)	1,475	(1,083)
Income (loss) before income taxes	(33,420)		11,546	(12,998)	18,017
Provision (benefit) for income taxes	10,093		3,624	9,530	(3,782)
Net income (loss)	(43,513)		7,922	(22,528)	21,799
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	315,499		307,883	654,256	614,527
Cost of revenue	77,967			153,163
Gross margin	237,532			501,093
Sales and marketing	109,421			216,725
Research and development	61,402			122,184
General and administrative	35,371			73,235
Amortization of acquired intangible assets	5,930			11,866
Restructuring and other charges, net	26,980			45,473
Total operating expenses	239,104			469,483
Operating income (loss)	(1,572)			31,610
Interest expense	(11,383)			(21,659)
Other income (expense), net	1,065			1,613
Income (loss) before income taxes	(11,890)			11,564
Provision (benefit) for income taxes	140			4,346
Net income (loss)	(12,030)			7,218
Software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	249,521		262,453	542,764	527,643
Cost of revenue	45,749		46,189	89,509	92,805
Software | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	276,901		262,453	576,289	527,643
Cost of revenue	45,222			88,199
Support and cloud services
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	187,645		141,948	375,566	287,620
Cost of revenue	32,874		34,335	64,071	68,837
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	120,770			246,253
Cost of revenue	32,977			63,607
License
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	61,876		120,505	167,198	240,023
Cost of revenue	12,875		11,854	25,438	23,968
License | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	156,131	$ 15,000		330,036
Cost of revenue	12,245			24,592
Professional services
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	40,930		45,430	82,376	86,884
Cost of revenue	34,155		37,519	67,747	73,938
Professional services | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	38,598		$ 45,430	77,967	$ 86,884
Cost of revenue	32,745			$ 64,964
Accounting Standards Update 2014-09 | License
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue	58,300	123,300
Revenue On New And Renewal Bookings	$ 48,500	$ 92,000