Fair Value Measurements (Change in Fair Value of Derivative Liabilities) (Details)	6 Months Ended
	Jun. 30, 2018 USD ($)
Derivatives And Fair Value [Line Items]
Balance, derivative liability	$ 292,000
Changes in estimated fair value	77,000
Exercised warrants	(184,000)
Balance, derivative liability	185,000
November 2016 Warrants [Member]
Derivatives And Fair Value [Line Items]
Balance, derivative liability	260,000
Changes in estimated fair value	81,000
Exercised warrants	(184,000)
Balance, derivative liability	157,000
June 2016 Offering Liability [Member]
Derivatives And Fair Value [Line Items]
Balance, derivative liability	32,000
Changes in estimated fair value	(4,000)
Balance, derivative liability	$ 28,000