Equity Incentive Plans (Allocation of Share-Based Compensation Expense) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	$ 261,000	$ 949,000	$ 1,118,000	$ 1,442,000
Research and development expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	259,000	489,000	804,000	679,000
General and administrative expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense	$ 2,000	$ 460,000	$ 314,000	$ 763,000