Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of Financial Assets and Liabilities at Fair value on a Recurring Basis

The Company measures the following financial assets at fair value on a recurring basis. There were no transfers between levels of the fair value hierarchy during any of the periods presented. The following tables set forth the Company’s financial assets and liabilities carried at fair value categorized using the lowest level of input applicable to each financial instrument as of December 31, 2020 and 2019 (in thousands):

			Quoted Prices
			in Active		Significant
			Markets for		Other		Significant
	Balance at		Identical		Observable		Unobservable
	December 31,		Assets		Inputs		Inputs
	2020		(Level 1)		(Level 2)		(Level 3)
Assets:
Certificates of deposit	$	1,251	$	—	$	1,251	$	—
US Treasury securities		34,147		34,147		—		—
Restricted cash		551		551		—		—
	$	35,949	$	34,698	$	1,251	$	—
Liabilities:
Derivative liability	$	1,010	$	—	$	—	$	1,010
	$	1,010	$	—	$	—	$	1,010

			Quoted Prices
			in Active		Significant
			Markets for		Other		Significant
	Balance at		Identical		Observable		Unobservable
	December 31,		Assets		Inputs		Inputs
	2019		(Level 1)		(Level 2)		(Level 3)
Assets:
Money market funds	$	4,301	$	4,301	$	—	$	—
Restricted cash		180		180		—		—
	$	4,481	$	4,481	$	—	$	—
Liabilities:
Derivative liability	$	2,425	$	—	$	—	$	2,425
	$	2,425	$	—	$	—	$	2,425

Summary of Contingent Interest Payments

The estimated fair value of the derivative at December 31, 2020 was determined using a probability-weighted discounted cash flow model that includes contingent interest payments under the following scenarios:

	Range
4% contingent interest beginning in 2021		0	%
4% contingent interest beginning in 2022		90	%

Roll-Forward of Fair Value of Derivative Liability

The following table provides a roll-forward of the fair value of the derivative liability (in thousands):

Balance at December 31, 2018	$	2,142
Change in fair value of derivative liability, recorded as interest    expense		283
Balance at December 31, 2019		2,425
Change in fair value of derivative liability, recorded as interest    expense		(1,415	)
Balance at December 31, 2020	$	1,010