Financial instruments (Tables)

12 Months Ended

Dec. 31, 2014

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:

December 31, 2014
Short-term investments:	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
U.S. treasury securities	$	12,199,357	$	—	$	(5,438	)	$	12,193,919
U.S. Government agency securities		11,995,946		1,354		—			11,997,300
	$	24,195,303	$	1,354	$	(5,438	)	$	24,191,219
Long-term investments:
U.S. Government agency securities	$	2,002,870	$	229	$	—		$	2,003,099
Contractual maturities:
Due within one year	$	24,195,303						$	24,191,219
Due after one year through two years		2,002,870							2,003,099

December 31, 2013
Short-term investments:	Amortized cost		Gross unrealized gains		Gross unrealized losses		Fair value
Bank guaranteed investment certificate	$	2,820,600	$	—	$	—	$	2,820,600
Contractual maturities:
Due within one year	$	2,820,600					$	2,820,600

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
December 31, 2014	Fair value		Gross unrealized losses			Fair value		Gross unrealized losses
U.S. treasury securities	$	12,193,919	$	(5,438	)		NA		NA
December 31, 2013		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 – December 31, 2014
Short-term investments – U.S. treasury securities	$	12,193,919	$	—	$	—		$	12,193,919
Short-term investments – U.S. government agency securities		11,997,300		—		—			11,997,300
Investments – U.S. treasury securities		—		—		—			—
Investments – U.S. government agency securities		2,003,099		—		—			2,003,099
Bank loan warrant derivative liabilities		—		—		(72,341	)		(72,341	)
	$	26,194,318	$	—	$	(72,341	)	$	26,121,977
BALANCES – December 31, 2013
Short-term investments – bank term deposits	$	—	$	2,820,600	$	—		$	2,820,600
Bank loan warrant derivative liabilities		—		—		(221,320	)		(221,320	)
Redemption option on preferred stock		—		—		(800,206	)		(800,206	)
	$	—	$	2,820,600	$	(1,021,526	)	$	1,799,074

Fair Value of Significant Unobservable Inputs

Fair value of significant unobservable inputs (Level 3):

	BANK LOAN WARRANT DERIVATIVE LIABILITIES			PREFERRED STOCK EMBEDDED DERIVATIVE LIABILITIES			TOTAL
BALANCES – December 31, 2013	$	221,320		$	800,206		$	1,021,526
Change in fair value of derivative liabilities		(148,979	)		—			(148,979	)
Derecognition of liabilities upon preferred stock conversion to common stock conversion		—			(800,206	)		(800,206	)
BALANCES – December 31, 2014	$	72,341		$	—		$	72,341