Financial instruments (Tables)

3 Months Ended

Mar. 31, 2015

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 are consisted of available-for-sale securities as follows:

March 31, 2015

	Amortized cost		Gross unrealized gains		Gross unrealized losses		Fair value
Short-term investments:
U.S. treasury securities	$	12,133	$	1	$	—	$	12,134
U.S. Government agency securities		7,999		2		—		8,001
	$	20,132	$	3	$	—	$	20,135
Contractual maturities:
Due within one year	$	20,132					$	20,135

December 31, 2014

	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Short-term investments:
U.S. treasury securities	$	12,199	$	—	$	(5	)	$	12,194
U.S. Government agency securities		11,996		1		—			11,997
	$	24,195	$	1	$	(5	)	$	24,191
Long-term investments:
U.S. Government agency securities	$	2,003	$	0	$	—		$	2,003
Contractual maturities:
Due within one year	$	24,195						$	24,191
Due after one year through two years		2,003							2,003

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
December 31, 2014
U.S. treasury securities	$	12,194	$	(5	)		NA		NA
March 31, 2015		NA		NA			NA		NA

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 – March 31, 2015
Short-term investments – U.S. treasury securities	$	12,134	$	—	$	—		$	12,134
Short-term investments – U.S. government agency securities		8,001		—		—			8,001
Bank loan warrant derivative liabilities		—		—		(79	)		(79	)
	$	20,135	$	—	$	(79	)	$	20,056
BALANCES – December 31, 2014
Short-term investments – U.S. treasury securities	$	12,194	$	—	$	—		$	12,194
Short-term investments – U.S. government agency securities		11,997		—		—			11,997
Long-term investments – U.S. government agency securities		2,003		—		—			2,003
Bank loan warrant derivative liabilities		—		—		(72	)		(72	)
	$	26,194	$	—	$	(72	)	$	26,122

Fair Value of Significant Unobservable Inputs

Fair value of significant unobservable inputs (Level 3):

Three months ended March 31, 2015:	BANK LOAN WARRANT DERIVATIVE LIABILITIES		TOTAL
BALANCES – December 31, 2014	$	72	$	72
Change in fair value of derivative liabilities		7		7
BALANCES – March 31, 2015	$	79	$	79