Note 4 - Cash, Cash Equivalents, and Restricted Cash (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Table Text Block]

	Year ended December 31,
(in thousands)	2019		2018
Cash	$	12,041	$	7,875
Cash equivalents:
U.S. Government money market funds		14,971		19,812
Tri-party reverse repurchase agreements (collateralized by at least 102% U.S. Treasury and Agency Securities)		154,258		165,157
Restricted cash, non-current		100		100
Total cash, cash equivalents, and restricted cash	$	181,370	$	192,944