Note 18 - Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2021

Notes Tables

Quarterly Financial Information [Table Text Block]

	Year Ended December 31, 2021
	First			Second			Third			Fourth
Revenue	$	506		$	112		$	200		$	74
Operating expenses	$	16,017		$	15,887		$	17,451		$	24,289
Net loss	$	(16,007	)	$	(16,116	)	$	(17,583	)	$	(20,764	)
Net loss per share – basic and diluted	$	(0.14	)	$	(0.13	)	$	(0.14	)	$	(0.17	)

	Year Ended December 31, 2020
	First			Second			Third			Fourth
Revenue	$	2,902		$	523		$	265		$	356
Operating expenses	$	3,596		$	9,049		$	7,854		$	13,717
Net loss	$	(1,297	)	$	(8,977	)	$	(8,085	)	$	(13,861	)
Net loss per share – basic and diluted	$	(0.02	)	$	(0.12	)	$	(0.08	)	$	(0.13	)

	Year Ended December 31, 2019
	First			Second			Third			Fourth
Revenue	$	5,407		$	85		$	454		$	3,916
Operating expenses	$	5,855		$	5,082		$	5,168		$	9,542
Net loss	$	(1,339	)	$	(5,637	)	$	(5,260	)	$	(6,409	)
Net loss per share – basic and diluted	$	(0.18	)	$	(0.39	)	$	(0.32	)	$	(0.13	)