Note 3 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Amortized Cost		$ 16,341	$ 31,995
Gross Unrealized Gains		1	2
Gross Unrealized Losses	[1]	2	7
Short-term investments		16,340	31,990	[2]
Corporate Debt Securities [Member]
Amortized Cost	[3]	9,843	22,513
Gross Unrealized Gains	[3]	1	1
Gross Unrealized Losses	[1],[3]	2	6
Short-term investments	[3]	9,842	22,508
US Treasury Securities [Member]
Amortized Cost		4,596
Gross Unrealized Gains
Gross Unrealized Losses	[1]
Short-term investments		4,596
US Government-sponsored Enterprises Debt Securities [Member]
Amortized Cost			8,109
Gross Unrealized Gains
Gross Unrealized Losses	[1]		1
Short-term investments			8,108
Certificates of Deposit [Member]
Amortized Cost		1,299	750
Gross Unrealized Gains			1
Gross Unrealized Losses	[1]
Short-term investments		1,299	751
Foreign Government Debt Securities [Member]
Amortized Cost		603	623
Gross Unrealized Gains
Gross Unrealized Losses	[1]
Short-term investments		$ 603	$ 623

[1] As of September 30, 2017, there were $7.5 million of investments in our portfolio in a loss position. As of December 31, 2016, the cost and fair value of investments with loss positions were approximately $26.6 million. We evaluated the nature of these investments, credit worthiness of the issuer and the duration of these impairments to determine if an other-than-temporary decline in fair value had occurred and concluded that these losses were temporary and we have the ability and intent to hold these investments to maturity.

[2] Derived from December 31, 2016 audited financial statements

[3] Corporate debt securities include investments in financial and other corporate institutions. No single issuer represents a significant portion of the total corporate debt securities portfolio.