Common Stock Issuance (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Cash received from stock sale, before issuance costs	$ 20,220,000	$ 19,356,000
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	<p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0">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.</p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"></p>
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	<p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0">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.</p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"></p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"></p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p>
Public August 2017
Number of shares of common stock issued	5,500,000
Cash received from stock sale, before issuance costs	$ 11,500,000
Stock issuance costs	$ 1,100,000
Terms and provisions	<p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0">In August 2017, we raised approximately $11.5 million before issuance costs of approximately $1.1 million through an underwritten public offering of 5.5 million shares of our common stock.</p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p>
Private Aug 2017
Number of shares of common stock issued	1,500,000
Cash received from stock sale, before issuance costs	$ 3,200,000
Stock issuance costs	$ 26,000
Terms and provisions	<p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0">In August 2017, we raised $3.2 million before issuance costs of approximately $26,000 through a private placement of 1.5 million shares of our common stock.</p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p>
Warrant Exercise 2nd Quarter 2017
Number of shares of common stock issued	460,000
Cash received from stock sale, before issuance costs	$ 906,000
Terms and provisions	<p style="margin: 0"><font style="font-size: 10pt"></font></p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0">During the second quarter of 2017, we received $906,000 from the exercise of warrants to purchase 460,000 shares of common stock, which warrants were issued in connection with earlier financing transactions.</p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"></p> <p style="font: 10pt Times New Roman, Times, Serif; margin: 0"> </p> <p style="margin: 0"><font style="font-size: 10pt"> </font></p> <p style="margin: 0"></p> <p style="margin: 0"><font style="font-size: 10pt"> </font></p>
ATM Agreement Terminated June 2017 2nd Quarter 2017
Number of shares of common stock issued	1,700,000
Cash received from stock sale, before issuance costs	$ 3,700,000
Stock issuance costs	$ 125,000
Terms and provisions	<p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0">During the second quarter of 2017, we received gross proceeds of $3.7 million before issuance costs of approximately $125,000 from the sale of 1.7 million shares of our common stock under an ATM agreement that was terminated in June 2017 at our election without penalty.</p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"></p> <p style="font: 10pt Times New Roman, Times, Serif; margin: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"></p> <p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0"> </p>
Agreement Terminated August 2017 2nd Quarter 2017
Number of shares of common stock issued	1,200,000
Cash received from stock sale, before issuance costs	$ 2,200,000
Terms and provisions	<p style="font: 10pt Times New Roman, Times, Serif; margin-right: 0; margin-left: 0">During the second quarter of 2017, we received proceeds of $2.2 million from the sale of 1.2 million shares of our common stock as part of a common stock purchase agreement entered into in September 2016 that was terminated in August 2017 at our election without penalty.</p> <p style="font: 10pt Times New Roman, Times, Serif; margin: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin: 0"> </p> <p style="font: 10pt Times New Roman, Times, Serif; margin: 0"> </p>