Note 7 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Total financial assets (liabilities)	$ 71,633
Foreign Exchange Forward [Member]
Derivative assets
Derivative liabilities
Short-term Investments [Member] | Term Bank Deposits [Member]
Short-term investments, at fair value	65,493
Money Market Funds [Member]
Cash equivalents	6,140
US Treasury Securities Included in Cash and Cash Equivalents [Member]
Short-term investments, at fair value
Fair Value, Inputs, Level 1 [Member]
Total financial assets (liabilities)	86,738	$ (479)
Fair Value, Inputs, Level 1 [Member] | Foreign Exchange Forward [Member]
Derivative assets
Derivative liabilities		(479)
Fair Value, Inputs, Level 1 [Member] | Short-term Investments [Member] | Term Bank Deposits [Member]
Short-term investments, at fair value	40,137
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Cash equivalents	6,870
Fair Value, Inputs, Level 1 [Member] | US Treasury Securities Included in Cash and Cash Equivalents [Member]
Short-term investments, at fair value	39,731
Fair Value, Inputs, Level 2 [Member]
Total financial assets (liabilities)	163	71,154
Fair Value, Inputs, Level 2 [Member] | Foreign Exchange Forward [Member]
Derivative assets	163
Derivative liabilities		(479)
Fair Value, Inputs, Level 2 [Member] | Short-term Investments [Member] | Term Bank Deposits [Member]
Short-term investments, at fair value		65,493
Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Cash equivalents		6,140
Fair Value, Inputs, Level 2 [Member] | US Treasury Securities Included in Cash and Cash Equivalents [Member]
Short-term investments, at fair value
Fair Value, Inputs, Level 3 [Member]
Total financial assets (liabilities)	86,901
Fair Value, Inputs, Level 3 [Member] | Foreign Exchange Forward [Member]
Derivative assets	163
Derivative liabilities
Fair Value, Inputs, Level 3 [Member] | Short-term Investments [Member] | Term Bank Deposits [Member]
Short-term investments, at fair value	40,137
Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Cash equivalents	6,870
Fair Value, Inputs, Level 3 [Member] | US Treasury Securities Included in Cash and Cash Equivalents [Member]
Short-term investments, at fair value	$ 39,731