Note 3 - Investment Securities (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Investment [Table Text Block]

	December 31,
	2017		2016
Cash and cash equivalents:
Cash	$	14,058	$	6,672
Cash equivalents:
Money market funds		126		6,053
Commercial paper		—		1,050
Total cash and cash equivalents		14,184		13,775
Marketable securities:
U.S. government notes		11,870		8,398
U.S. government agencies		—		3,916
Municipal securities		200		1,325
Commercial paper		1,833		12,299
Corporate debt securities		7,825		14,361
Total marketable securities		21,728		40,299
Total cash, cash equivalents and marketable securities	$	35,912	$	54,074

Unrealized Gain (Loss) on Investments [Table Text Block]

December 31, 2017	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Market Value
Cash and cash equivalents	$	14,184	$	—	$	—		$	14,184
Marketable investments
U.S. government notes		11,885		—		(15	)		11,870
U.S. government agencies		—		—		—			—
Municipal securities		201		—		(1	)		200
Commercial paper		1,836		—		(3	)		1,833
Corporate debt securities		7,838		2		(15	)		7,825
Total marketable securities		21,760		2		(34	)		21,728
Total cash, cash equivalents and marketable securities	$	35,944	$	2	$	(34	)	$	35,912

December 31, 201 6	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Market Value
Cash and cash equivalents	$	13,775	$	—	$	—		$	13,775
Marketable investments
U.S. government notes		8,403		4		(9	)		8,398
U.S. government agencies		3,918		—		(2	)		3,916
Municipal securities		1,325		—		—			1,325
Commercial paper		12,299		2		(2	)		12,299
Corporate debt securities		14,366		3		(8	)		14,361
Total marketable securities		40,311		9		(21	)		40,299
Total cash, cash equivalents and marketable securities	$	54,086	$	9	$	(21	)	$	54,074

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amount
Due in less than one year (fiscal year 201 8)	$	19,109
Due in 1 to 3 years (fiscal year 2019)		2,619
Total marketable securities	$	21,728

Fair Value Measurements, Recurring and Nonrecurring [Table Text Block]

December 31, 2017	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	126	$	—	$	—	$	126
Commercial paper		—		—		—		—
Short term marketable investments:
Available-for-sale securities		—		21,728		—		21,728
Total assets at fair value	$	126	$	21,728	$	—	$	21,854

December 31, 2016	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	6,053	$	—	$	—	$	6,053
Commercial paper		—		1,050		—		1,050
Short term marketable investments:
Available-for-sale securities		—		40,299		—		40,299
Total assets at fair value	$	6,053	$	41,349	$	—	$	47,402