Goodwill and Purchased Intangible Assets, Finite Lived Intangible Assets by Class (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Purchased Intangible Assets [Line Items]
Gross	$ 725,900,000	$ 710,500,000
Accumulated amortization	594,100,000	576,600,000
Impairment and other charges	(52,700,000)	(52,700,000)
Net	79,100,000	81,200,000
Total purchased intangible assets, gross	774,900,000	759,500,000
Purchased intangible assets, net	128,100,000	130,200,000
Amortization of intangible assets	17,500,000	16,300,000	$ 28,500,000
Impairment of intangible assets	0	0
Cost of revenues
Purchased Intangible Assets [Line Items]
Acceleration of the end of life of certain intangible assets, finite-lived			$ 5,600,000
IPR&D
Purchased Intangible Assets [Line Items]
Indefinite-lived intangible assets:	49,000,000	49,000,000
Technologies and patents
Purchased Intangible Assets [Line Items]
Gross	640,300,000	624,900,000
Accumulated amortization	518,100,000	504,200,000
Impairment and other charges	(49,900,000)	(49,900,000)
Net	72,300,000	70,800,000
Customer contracts, support agreements, and related relationships
Purchased Intangible Assets [Line Items]
Gross	83,600,000	83,600,000
Accumulated amortization	74,100,000	70,800,000
Impairment and other charges	(2,800,000)	(2,800,000)
Net	6,700,000	10,000,000
Other
Purchased Intangible Assets [Line Items]
Gross	2,000,000	2,000,000
Accumulated amortization	1,900,000	1,600,000
Impairment and other charges	0	0
Net	$ 100,000	$ 400,000