Other Financial Information (Narrative) (Details)	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Deferred commission	$ 26,300,000	$ 26,300,000
Amortization of deferred commission	37,700,000	78,200,000
Impairment loss	0	0
Product
Disaggregation of Revenue [Line Items]
Contract with customer, liability, revenue recognized	17,000,000	56,500,000
Service
Disaggregation of Revenue [Line Items]
Contract with customer, liability, revenue recognized	$ 166,300,000	$ 431,300,000