General (Details Textual)				3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) subsidiary	Dec. 31, 2018	Mar. 31, 2014 USD ($)	Sep. 30, 2019 USD ($) subsidiary	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) subsidiary	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operations commenced date						Jan. 01, 2005
Subsidiary or equity method investee, number | subsidiary	10			10		10
Entity incorporation, date of incorporation						Nov. 24, 2004
Deferred revenue, revenue recognized						$ 76,026,000
Sales returns						$ 0		$ 0
Capitalized contract cost, amortization period (years)	4 years			4 years		4 years
Ineffective hedges recognized				$ 0	$ 0
Gain in financial income, net				951,000		$ 1,404,000
Loss in financial income, net					199,000		$ 199,000
Other than temporary impairment losses, investments, available-for-sale securities						0
Operating lease right-of-use asset	$ 57,046,000			57,046,000		57,046,000
Operating lease liabilities, current	(7,287,000)			(7,287,000)		(7,287,000)
Operating lease liabilities long-term	$ (58,667,000)			(58,667,000)		(58,667,000)
Foreign Exchange Contract
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Derivative, gain (loss) on derivative, net, total				$ 361,000	$ (1,194,000)	(170,000)	(2,094,000)
Ineffective hedges recognized						$ 0	$ 0
US Treasury Securities | Maximum | Short-term deposits
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term Investment, maturity period	1 year	1 year
Promissory Note
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Line of credit facility, maximum borrowing capacity			$ 7,000,000
Basis spread on variable rate (percentage)			0.05%
Interest rate at period end	5.05%			5.05%		5.05%
Long-term line of credit	$ 0			$ 0		$ 0
Promissory Note | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest rate, effective percentage			4.10%
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Elimination of deferred rent, current									$ 1,313,000
Elimination of deferred rent, noncurrent									4,236,000
Operating lease right-of-use asset									53,274,000
Operating lease liabilities, current									(2,349,000)
Operating lease liabilities long-term									$ (55,676,000)
Maintenance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, performance obligation, description of timing						one year