Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Assets and Liabilities Carried at Fair Value Measured on Recurring Basis

The following tables summarize the Company’s assets carried at fair value measured on a recurring basis at June 30, 2019 and December 31, 2018 by valuation hierarchy (in thousands):

	June 30, 2019
			Quoted prices in		Significant other		Significant
	Total Carrying		active markets		observable inputs		unobservable inputs
Description	Value		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash equivalents	$	43,202	$	43,202	$	—	$	—
	$	43,202	$	43,202	$	—	$	—

	December 31, 2018
			Quoted prices in		Significant other		Significant
	Total Carrying		active markets		observable inputs		unobservable inputs
Description	Value		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash equivalents	$	43,194	$	43,194	$	—	$	—
	$	43,194	$	43,194	$	—	$	—

Summary of Changes in the Fair Value of the Company's Derivative Liability

The following table sets forth a summary of changes in the fair value of the Company’s derivative liability for which fair value was determined by Level 3 inputs (in thousands):

	Second Tranche Liability			Additional Advance Warrant Liability			Second Tranche Warrants		Total
Balance at January 1, 2018	$	—		$	—		$	—	$	—
Initial fair value of derivative liability		4,734			69			18,165		22,968
Change in fair value		24,319			18			1,615		25,952
Reclassification to equity		—			(87	)		—		(87	)
Settlement		(29,053	)		—			—		(29,053	)
Balance at June 30, 2018	$	—		$	—		$	19,780	$	19,780

Additional Advance Warrant Liability [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Schedule of Assumptions Used to Value Liability

	March 28, 2018 (Date of Issuance)			June 25, 2018 (Date of Reclassification to Equity)
Volatility		55.20	%		55.10	%
Risk free interest rate		1.70	%		2.80	%
Term (in years)	7			7
Dividend rate		0	%		0	%
Valuation date stock price	$	1.07		$	1.93
Probability of issuance		80	%		100	%

Second Tranche Transaction Liability [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Schedule of Assumptions Used to Value Liability

Significant assumptions used to value this liability were as follows:

	March 28, 2018 (Date of Issuance)			June 25, 2018 (Date of Settlement)
Volatility		54.20	%	N/A
Risk free interest rate		1.70	%	N/A
Estimated date of stockholder    approval	June 2018			N/A
Estimated number of units issuable		26,900,000			20,184,224
Valuation date stock price	$	1.07		$	1.93

Second Tranche Warrants [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Schedule of Assumptions Used to Value Liability

  Significant assumptions used to value this liability prior to exercise in September 2018 were as follows:

	June 25, 2018 (Date of issuance)			June 30, 2018
Volatility		81.00	%		85.40	%
Risk free interest rate		2.10	%		2.10	%
Term (in years)	0.5			0.5
Dividend rate		0	%		0	%
Valuation date stock price	$	2.00		$	2.08
Probability of issuance		100	%		100	%