Note 1 - General (Details Textual) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Operations Commenced Date	Jan. 01, 2005
Subsidiary or Equity Method Investee, Number	8
Entity Incorporation, Date of Incorporation	Nov. 24, 2004
Revenue from Contract with Customer, Including Assessed Tax	$ 53,528	$ 39,593
Deferred Revenue, Current	68,481		$ 73,493
Deferred Revenue, Noncurrent	6,247		6,608
Contract with Customer, Liability, Revenue Recognized	27,952
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Total	$ 0
Short-term Investments [Member] \| US Treasury Securities [Member] \| Maximum [Member]
Short-term Investment, Maturity Period	1 year
Foreign Exchange Contract [Member]
Derivative, Gain (Loss) on Derivative, Net, Total	$ 48	265
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net, Total	0	0
Accounting Standards Update 2014-09 [Member] \| As of December 31, 2017 [Member]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 13,064
Accounting Standards Update 2014-09 [Member] \| Restatement Adjustment [Member]
Revenue from Contract with Customer, Including Assessed Tax		$ (787)	(1,974)
Deferred Sales Commission			13,486
Deferred Revenue, Current			(398)
Deferred Revenue, Noncurrent			(426)
Deferred Tax Liabilities, Net, Noncurrent			$ 1,246

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