Note 14 - Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

December 31, 2019	Total		Level 1		Level 2
Assets
Cash equivalents:
Money market funds	$	190,598	$	67,494	$	123,104
Commercial paper		9,465		—		9,465
Municipal bonds		1,250		—		1,250
Investments in marketable securities:
U.S. Treasury securities		3,759		3,759		—
Municipal bonds		6,119		—		6,119
Corporate notes/bonds		119,449		—		119,449
Asset-backed securities		4,268		—		4,268
Commercial paper		6,464		—		6,464
Certificate of deposit		72		72		—
	$	341,444	$	71,325	$	270,119

December 31, 2018	Total		Level 1		Level 2
Assets
Cash equivalents:
Money market funds	$	740	$	38	$	702
Commercial paper		96,759		—		96,759
Investments in marketable securities:
Municipal bonds		6,733		—		6,733
Corporate notes/bonds		146,126		—		146,126
Variable rate demand notes		8,900		—		8,900
Asset-backed securities		32,923		—		32,923
Commercial paper		39,701		—		39,701
Certificate of deposit		956		956		—
	$	332,838	$	994	$	331,844