Note 4 - Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2016

Notes Tables

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

			Fair Value Measurements at Reporting Date Using
	December 31, 2016		Quoted Prices in Active Markets  for Identical Assets   (Level 1)		Significant Other  Observable Inputs   (Level 2)		Significant   Unobservable Inputs   (Level 3)
Cash equivalents:
Money market funds	$	68,352	$	-	$	68,352	$	-
Bank certificates of deposit		750		-		750		-
Total cash equivalents		69,102		-		69,102		-
Investments:
Bank certificates of deposit	$	20,500	$	-	$	20,500	$	-

			Fair Value Measurements at Reporting Date Using
	December 31, 2015		Quoted Prices in Active Markets  for Identical Assets  (Level 1)		Significant Other  Observable Inputs  (Level 2)		Significant   Unobservable Inputs  (Level 3)
Cash equivalents:
Money market funds	$	61,385	$	-	$	61,385	$	-
Bank certificates of deposit		250		-		250		-
Total cash equivalents	$	61,635	$	-	$	61,635	$	-
Investments:
Corporate debt securities	$	2,001	$	-	$	2,001	$	-
Bank certificates of deposit		25,750		-		25,750		-
Total investments	$	27,751	$	-	$	27,751	$	-