Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Schedule of cash and available-for-sale securities’ adjusted cost, gross unrealized gains, gross unrealized losses and fair values by significant investment category

The following table presents the Company’s cash, cash equivalents, restricted cash, and marketable securities as of December 31, 2017 and 2016 (in thousands):

	December 31, 2017
	Adjusted Cost		Unrealized Gains		Unrealized Losses			Fair Value		Cash and Cash Equivalents		Restricted Cash		Marketable Securities
Cash	$	6,783	$	—	$	—		$	6,783	$	5,370	$	1,413	$	—
Level 1 (1):
Money market funds	11,187		—		—			11,187		11,187		—		—
U.S. treasury securities	1,991		—		—			1,991		—		—		1,991
Subtotal	13,178		—		—			13,178		11,187		—		1,991
Level 2 (2):
U.S. government agency securities	47,594		—		(42		)	47,552		—		—		47,552
Total	$	67,555	$	—	$	(42	)	$	67,513	$	16,557	$	1,413	$	49,543

	December 31, 2016
	Adjusted Cost		Unrealized Gains		Unrealized Losses			Fair Value		Cash and Cash Equivalents		Restricted Cash		Marketable Securities
Cash	$	13,756	$	—	$	—		$	13,756	$	12,563	$	1,193	$	—
Level 1 (1):
Money market funds	10,043		—		—			10,043		10,043		—		—
Level 2 (2):
Repurchase agreements	1,660							1,660		1,660
U.S. government agency securities	86,333		19		(17		)	86,335		—		—		86,335
Subtotal	87,993		19		(17		)	87,995		1,660		—		86,335
Total	$	111,792	$	19	$	(17	)	$	111,794	$	24,266	$	1,193	$	86,335

(1) The fair value of Level 1 securities is estimated based on quoted prices in active markets for identical assets or liabilities.

(2) The fair value of Level 2 securities is estimated based on observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term on the assets or liabilities.

Schedule of changes in the fair value of the Company's warrant liability representing a recurring measurement classified within Level 3, wherein fair value is estimated using significant unobservable inputs

The following table sets forth a summary of changes in the fair value of this warrant liability, which represents a recurring measurement that is classified within Level 3 of the fair value hierarchy, wherein fair value is estimated using significant unobservable inputs (in thousands):

	Warrant Liability
Balance as of January 1, 2016	$	153
Amounts acquired or issued	—
Changes in estimated fair value	(78		)
Balance as of December 31, 2016	75
Amounts acquired or issued	—
Changes in estimated fair value	(65		)
Balance as of December 31, 2017	$	10

Schedule of assumptions used for valuation of warrants

The following assumptions were used at December 31, 2017 and 2016 to determine the warrant liability:

	December 31,
	2017			2016
Estimated remaining term	4.3 years			5.3 years
Risk-free interest rate	2.1		%	2.0		%
Volatility	77.6		%	77.2		%
Dividend yield	—		%	—		%
Fair value of underlying instrument*	$	1.60		$	5.88

*Trevena, Inc. closing stock price.