SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash equivalents maturities, months	3 months
Impairment charge	$ 0	$ 0	$ 0
Severance pay expense	9,862	9,970	8,936
Expense for matching contributions	7,044	3,930	4,310
Advertising expenses	13,543	9,693	7,986
Retained earnings	850,772	710,910
Assets	2,845,086	2,631,876
Excess tax benefit from share-based payment arrangements		$ 7,868	$ 7,595
Cumulative effect of deferred revenues	39,000
Costs related to obtaining customer contracts	$ 45,000
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in computation of diluted earnings per share	249,274	398,544	561,621
Exchangeable Note Hedge [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in computation of diluted earnings per share	3,457,475
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded in computation of diluted earnings per share	3,457,475
Cumulative effect adjustment [Member]
Retained earnings	$ 0	$ 6,208
Assets	0
Liabilities	$ 0

The original period of time which a cash and cash equivalent matures.

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Amount of increase in additional paid in capital (APIC) resulting from a tax benefit associated with share-based compensation plan other than an employee stock ownership plan (ESOP). Includes, but is not limited to, excess tax benefit.

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Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

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Amount of deferred costs for long-term contracts and programs. Includes, but is not limited to, initial tooling costs and deferred production costs.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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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 cost for defined contribution plan.

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Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future.

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation.

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