Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Financial Instruments [Abstract]

Fair Values of Financial Instruments

	Fair Value Measurement Using:
	December 31,		Significant Other Observable Inputs		Significant Unobservable Inputs
Description	2016		(Level 2)		(Level 3)
Warrants	$	3,305	$	3,305	$	—
Total	$	3,305	$	3,305	$	—
	December 31,		Significant Other Observable Inputs		Significant Unobservable Inputs
Description	2017		(Level 2)		(Level 3)
Warrants	$	1,952	$	1,952	$	—
Total	$	1,952	$	1,952	$	—

Rollforward of Level 2 and Level 3 Investments

	Significant Other Observable Inputs		Significant Unobservable Inputs
	(Level 2)		(Level 3)
Balance as of January 1, 2016	$	—	$	8,289
Transfer of warrants from Level 3 to Level 2		6,300		(6,300)
Change in fair value of financial instruments		(4,107)		(273)
Beneficial conversion feature recognized on warrants issued in connection with 2015 credit agreement		1,112		—
Reclassification of warrants to APIC in connection with IPO		—		(1,716)
Balance as of December 31, 2016	$	3,305	$	—
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)		—
Balance as of December 31, 2017	$	1,952	$	—