Financial Instruments (Rollforward of Level 2 and Level 3 Investments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Significant Other Observable Inputs (Level 2) [Member]
Balance	$ 3,305
Transfer of warrants from Level 3 to Level 2		$ 6,300
Fair value of warrants modified in the Third Amendment	(908)
Issuance of warrants in private placement	1,651
Change in fair value of financial instruments	(2,096)	(4,107)
Beneficial conversion feature recognized on warrants issued in connection with 2015 credit agreement		1,112
Balance	$ 1,952	3,305
Significant Unobservable Inputs (Level 3) [Member]
Balance		8,289
Transfer of warrants from Level 3 to Level 2		(6,300)
Change in fair value of financial instruments		(273)
Reclassification of warrants to APIC in connection with IPO		$ (1,716)