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Segment Reporting Information, Percent Of Subscription Contracts Billable Upon Signing For Twelve Months Of Service

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Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

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The number of countries in which the entity operates as of balance sheet date.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Business and Basis of Presentation - Narrative (Details) employee in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2017 USD ($)	Jun. 30, 2018 USD ($) segment country employee	Jun. 30, 2017 USD ($) segment	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of organizations Company serves \| employee		15
Number of countries in which entity operates \| country		100
Number of reportable segments \| segment		4	4,000
Segment Reporting Information [Line Items]
Cash used in investing activities		$ (366,416)	$ 2,645,805
Cash and cash equivalents and restricted cash		159,956	$ 632,567		$ 567,058	$ 499,354
Restatement Adjustment \| Accounting Standards Update 2016-18
Segment Reporting Information [Line Items]
Cash used in investing activities	$ 18,200
Cash and cash equivalents and restricted cash		$ 43,300			$ 25,100
Retained Earnings \| Accounting Standards Update 2016-16
Segment Reporting Information [Line Items]
Cumulative effect of new accounting principle in period of adoption				$ 13,700
Revenue \| Research \| Product Concentration Risk
Segment Reporting Information [Line Items]
Percentage of segment revenues derived from subscription contracts		90.00%
Minimum
Segment Reporting Information [Line Items]
Percent of subscription contracts billable upon signing for twelve months of service		75.00%
Maximum
Segment Reporting Information [Line Items]
Percent of subscription contracts billable upon signing for twelve months of service		80.00%