Fair value of financial instruments (Tables)

12 Months Ended

Dec. 31, 2018

Fair value of financial instruments

Schedule of hierarchy for financial instruments measured at fair value on a recurring basis

		Fair Value as of December 31, 2018
	Level 1		Level 2		Level 3		Total
		(in thousands)
Cash and cash equivalents	$	27,419	$	19,059	$	—	$	46,478
Total financial assets	$	27,419	$	19,059	$	—	$	46,478
Earnout liability	$	—	$	—	$	37	$	37
Derivative liability (see Note 11)		—		—		2,017		2,017
Total financial liabilities	$	—	$	—	$	2,054	$	2,054

	Fair Value as of December 31, 2017
	Level 1		Level 2		Level 3		Total
	(in thousands)
Cash and cash equivalents	$	31,969	$	—	$	—	$	31,969
Short-term investments		—		18,448		—		18,448
Total financial assets	$	31,969	$	18,448	$	—	$	50,417
Earnout liability	$	—	$	—	$	170	$	170
Derivative liability (see Note 11)		—		—		1,660		1,660
Total financial liabilities	$	—	$	—	$	1,830	$	1,830

Schedule of cash and cash equivalents and short-term investments

	December 31, 2018
	Amortized		Unrealized		Market
	Cost		Loss		Value
	(in thousands)
Bank deposits and money market funds	$	27,419	$	—	$	27,419
Financial and corporate debt securities		19,059		—		19,059
	$	46,478	$	—	$	46,478

	December 31, 2017
	Amortized		Unrealized		Market
	Cost		Loss		Value
	(in thousands)
Bank deposits and money market funds	$	31,969	$	—	$	31,969
Financial and corporate debt securities		18,454		(6)		18,448
	$	50,423	$	(6)	$	50,417

Schedule of changes in Level 3 liabilities measured at fair value

	Level 3
	Liabilities
	(in thousands)
Balance at December 31, 2016	$	232
Addition of Deerfield derivative liability		2,107
Change in fair value		(509)
Balance at December 31, 2017		1,830
Change in fair value		224
Balance at December 31, 2018	$	2,054

Earnout liability

Fair value of financial instruments

Methodologies and significant inputs used in determination of fair value

	December 31, 2018	December 31, 2017
	Earnout Liability	Earnout Liability
Date of Valuation	12/31/2018	12/31/2017
Valuation Method	Monte Carlo	Monte Carlo
Volatility (annual)	42%	42%
Risk‑free rate (annual)	2.53% - 3.29%	1.62% ‑ 2.88%
Time period from valuation until end of earnout	.5 ‑ 9.5	.5 ‑ 9.5
Earnout Target 1 (thousands)	$13,700	$13,700
Earnout Target 2 (thousands)	$18,200	$18,200
Discount rate	21.35% - 21.68%	14.72% ‑ 15.98%
Fair value of liability at valuation date (thousands)	$37	$170

Derivative liability

Fair value of financial instruments

Methodologies and significant inputs used in determination of fair value

	DerivativeLiability
Date of Valuation	12/31/2018	12/31/2017
Valuation Method	Monte Carlo	Monte Carlo
Volatility (annual)	N/A	N/A
Time period from valuation until maturity of debt (yrs.)	3.4	4.4
Cumulative probability of a change in control prepayment implied by model	25.1%	27%
Cumulative probability of other accelerated prepayments implied by model	13.7%	17%
Discount rate	23.12%	16.20%
Fair value of liability at valuation date (thousands)	$2,017	$1,660