Note 3 - Financial Instruments (Details) - Summary of Assets and Liabilities Measured at Fair Value (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financial assets
Assets	$ 79,519	$ 83,585
Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]
Financial assets
Assets	9,778	68,830
Fair Value, Inputs, Level 1 [Member] | US Government Agencies Debt Securities [Member]
Financial assets
Assets	64,452	6,508
Fair Value, Inputs, Level 1 [Member]
Financial assets
Assets	74,230	75,338
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Financial assets
Assets	5,289	8,247
Fair Value, Inputs, Level 2 [Member]
Financial assets
Assets	5,289	8,247
Cash Equivalents [Member]
Financial assets
Assets	9,778	68,830
US Government Agencies Debt Securities [Member]
Financial assets
Assets	64,452	6,508
Corporate Debt Securities [Member]
Financial assets
Assets	$ 5,289	$ 8,247