Common Stock Issuance (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash received from stock sale, before issuance costs	$ 16,775,000	$ 20,220,000
Purchase Agreement December 2019
Number of shares of common stock issued	375,000
Cash received from stock sale, before issuance costs	$ 277,000
Stock issuance costs	$ 90,000
Terms and provisions	In December 2019, we entered into a Common Stock Purchase Agreement with Lincoln Park granting us the right to sell shares of our common stock having an aggregate value of up to $16.0 million. Under the terms of the agreement, Lincoln Park made an initial purchase of 1.5 million shares of common stock for $1.0 million at a purchase price of $0.6531 per share. Subject to various limitations and conditions set forth in the agreement, we may sell up to an additional $15.0 million in shares of common stock, from time to time, at our sole discretion to Lincoln Park over a 24-month period beginning December 2019. In consideration for entering into the agreement, we issued 375,000 shares of our common stock, having a value of $277,000, based on the closing stock price at the date of grant, to Lincoln Park as a commitment fee. We incurred an additional $90,000 in issuance costs.
Direct July 2019
Number of shares of common stock issued	3,000,000
Cash received from stock sale, before issuance costs	$ 2,000,000
Stock issuance costs	$ 24,000
Terms and provisions	In July 2019, we raised $2.0 million before issuance costs of approximately $24,000 through a registered direct offering of 3.0 million shares of our common stock to a private investor.
Direct April 2019
Number of shares of common stock issued	2,300,000
Cash received from stock sale, before issuance costs	$ 2,000,000
Stock issuance costs	$ 34,000
Terms and provisions	In April 2019, we raised $2.0 million before issuance costs of approximately $34,000 through a registered direct offering of 2.3 million shares of our common stock to a private investor.
Purchase Agreement April 2019
Number of shares of common stock issued	15,700,000
Cash received from stock sale, before issuance costs	$ 11,000,000
Terms and provisions	In April 2019, we entered into a Common Stock Purchase Agreement with Lincoln Park granting us the right to sell shares of our common stock having an aggregate value of up to $11.0 million. Under the terms of the agreement, Lincoln Park made an initial purchase of $1.0 million in shares of common stock at a purchase price of $0.98 per share. Subject to various limitations and conditions set forth in the agreement, we may sell up to an additional $10.0 million in shares of common stock, from time to time, at our sole discretion to Lincoln Park over a 24-month period beginning April 2019. In consideration for entering into the agreement, we issued 250,000 shares of our common stock, having a value of $258,000, based on the closing stock price at the date of grant, to Lincoln Park as a commitment fee. We incurred an additional $92,000 in issuance costs. As of December 31, 2019, we have issued 15.7 million shares and raised a total of $11.0 million under this agreement. No further shares are available for sales under this agreement.
Direct January 2019
Number of shares of common stock issued	2,000,000
Cash received from stock sale, before issuance costs	$ 1,200,000
Stock issuance costs	$ 26,000
Terms and provisions	In January 2019, we raised $1.2 million before issuance costs of approximately $26,000 through a registered direct offering of 2.0 million shares of our common stock to a private investor.
Public December 2018
Number of shares of common stock issued	7,000,000
Cash received from stock sale, before issuance costs	$ 4,200,000
Stock issuance costs	$ 524,000
Terms and provisions	In December 2018, we raised $4.2 million before issuance costs of approximately $524,000 through an underwritten public offering of 7.0 million shares of our common stock.
Public June 2018
Number of shares of common stock issued	14,400,000
Cash received from stock sale, before issuance costs	$ 18,000,000
Stock issuance costs	$ 1,400,000
Terms and provisions	In June 2018, we raised $18.0 million before issuance costs of approximately $1.4 million through an underwritten public offering of 14.4 million shares of our common stock.