Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) customer distributor	Dec. 31, 2017 USD ($) customer distributor	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	6 years 1 month 21 days	6 years 2 months 12 days
Amortization of capitalized contract costs	$ 38,100,000
Asset impairment charges related to contract assets	0
Allowance for doubtful accounts	3,600,000	$ 3,400,000
Amount capitalized related to internal use software	14,800,000	41,500,000
Amount expensed related to internal use software	25,900,000	27,300,000	$ 37,800,000
Capitalized costs for internally developed software to be sold as a service	7,300,000	15,200,000
Amount expensed related to internally developed computer software to be sold as a service	14,400,000	18,500,000	16,800,000
Advertising costs	99,100,000	85,600,000	72,800,000
Pension Plan | Foreign Plan
Significant Accounting Policies [Line Items]
Termination indemnities	11,200,000	13,200,000
Termination indemnities, compensation expense	$ 1,800,000	$ 2,600,000	$ 2,500,000
Minimum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	3 years
Licensing agreement term	1 year
Maximum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	7 years
Licensing agreement term	5 years
Customer concentration risk | Accounts receivable
Significant Accounting Policies [Line Items]
Number of major distributors | distributor	1	1
Number of customers meeting concentration risk threshold | customer	1	1
Contract-Based Intangible Assets [Member] | Minimum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	2 years
Contract-Based Intangible Assets [Member] | Maximum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	5 years
Internal use software | Minimum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	3 years
Internal use software | Maximum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	7 years
Internally developed software to be sold as a service
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	2 years
Arrow Group | Customer concentration risk | Accounts receivable
Significant Accounting Policies [Line Items]
Concentration risk percentage	17.00%	14.00%
Forecast | Minimum
Significant Accounting Policies [Line Items]
Operating lease, right-of-use assets				$ 200,000,000
Operating lease, liabilities				200,000,000
Forecast | Maximum
Significant Accounting Policies [Line Items]
Operating lease, right-of-use assets				250,000,000
Operating lease, liabilities				$ 250,000,000