Financial instruments (Tables)

6 Months Ended

Jun. 30, 2016

Investments, All Other Investments [Abstract]

Summary of Short-Term Investments and Long-Term Investments of Available-for-Sale Securities

The Company’s short-term investments and long-term investments consist of available-for-sale securities as follows:

June 30, 2016

	Amortized cost		Gross unrealized gains		Gross unrealized losses		Fair value
Short-term investments:
U.S. treasury securities	$	44,062	$	27	$	—	$	44,089
Long-term investments:
U.S. treasury securities	$	32,619	$	45	$	—	$	32,664
Contractual maturities:
Due within one year	$	44,062					$	44,089
Due after one year through two years		32,619						32,664

December 31, 2015

	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Short-term investments:
U.S. treasury securities	$	33,014	$	—	$	(61	)	$	32,953
U.S. government agency securities		2,003		—		—			2,003
	$	35,017	$	—	$	(61	)	$	34,956
Long-term investments:
U.S. treasury securities	$	38,687	$	—	$	(229	)	$	38,458
Contractual maturities:
Due within one year	$	35,017						$	34,956
Due after one year through two years		38,687							38,458

Aggregate Estimated Fair Value of Investments with Unrealized Losses

The aggregate estimated fair value of the Company’s investments with unrealized losses are as follows:

	Period of continuous unrealized loss
	12 months or less					Greater than 12 months
	Fair value		Gross unrealized losses			Fair value		Gross unrealized losses
June 30, 2016
U.S. treasury securities	$	5,498	$	—			N/A		N/A
December 31, 2015
U.S. treasury securities	$	71,411	$	(290	)		N/A		N/A

Fair Value of Financial Instruments Measured At Fair Value on a Recurring Basis

The following tables present the fair value of our financial instruments that are measured at fair value on a recurring basis:

	QUOTED PRICES IN ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1)		OTHER OBSERVABLE INPUTS (LEVEL 2)		SIGNIFICANT UN- OBSERVABLE INPUTS (LEVEL 3)			TOTAL
BALANCES – June 30, 2016
Short-term investments – U.S. treasury securities	$	44,089	$	—	$	—		$	44,089
Long-term investments – U.S. treasury securities		32,664		—		—			32,664
Bank loan warrant derivative liabilities		—		—		(51	)		(51	)
	$	76,753	$	—	$	(51	)	$	76,702
BALANCES – December 31, 2015
Short-term investments – U.S. treasury securities	$	32,953	$	—	$	—		$	32,953
Short-term investments – U.S. government agency securities		2,003		—		—			2,003
Long-term investments – U.S. treasury securities		38,458		—		—			38,458
Bank loan warrant derivative liabilities		—		—		(124	)		(124	)
	$	73,414	$	—	$	(124	)	$	73,290

Fair Value of Significant Unobservable Inputs

Fair value of significant unobservable inputs (Level 3):

	BANK LOAN WARRANT DERIVATIVE LIABILITIES
Three months ended June 30, 2016:
BALANCES – March 31, 2016	$	74
Change in fair value of derivative liabilities		(23	)
BALANCES – June 30, 2016	$	51
Six months ended June 30, 2016:
BALANCES – December 31, 2015	$	124
Change in fair value of derivative liabilities		(73	)
BALANCES – June 30, 2016	$	51