Marketable Securities and Fair Value Measurements

The guidance regarding fair value measurements establishes a three-tier fair value hierarchy which prioritizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets that are accessible at the measurement date; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions.

Assets and liabilities are classified based on the lowest level of input that is significant to the fair value measurements. The Company reviews the fair value hierarchy classification on a quarterly basis. Changes in the ability to observe valuation inputs may result in a reclassification of levels for certain securities within the fair value hierarchy. The Company did not have any transfer of assets and liabilities between Level 1, Level 2 and Level 3 of the fair value hierarchy during the years ended December 31, 2017 and 2016.

The following table presents the Company’s assets and liabilities that are measured at fair value on a recurring basis, and are determined using the following inputs as of December 31, 2017:



	Fair Value Measurements at
	December 31, 2017
	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Unobservable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Money market funds	$	9,843,482	$	9,843,482	$	—	$	—
Mutual funds	68,565,889		—		68,565,889		—
US corporate debt securities	35,072,955		—		35,072,955		—
Investments in affiliated entities	11,394,480		11,394,480		—		—
Total assets	$	124,876,806	$	21,237,962	$	103,638,844	$	—
Liabilities:
Common stock warrants	$	360,795			$	—	$	360,795
Total liabilities	$	360,795			$	—	$	360,795

The following table presents the Company’s assets and liabilities that are measured at fair value on a recurring basis, and are determined using the following inputs as of December 31, 2016:



	Fair Value Measurements at
	December 31, 2016
	Total		Quoted Prices in Active Markets (Level 1)		Significant Other Unobservable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets:
Money market funds	$	10,300,813	$	10,300,813	$	—	$	—
Mutual funds	60,589,746		—		60,589,746		—
US corporate debt securities	25,039,666		—		25,039,666		—
Investments in affiliated entities	19,829,575		19,829,575		—		—
Total assets	$	115,759,800	$	30,130,388	$	85,629,412	$	—
Liabilities:
Common stock warrants	$	1,167,614	$	—	$	—	$	1,167,614
Total liabilities	$	1,167,614	$	—	$	—	$	1,167,614

Level 1 assets at December 31, 2017 and 2016 consisted of money market funds held by the Company that are valued at quoted market prices, as well as the Company’s investments in GeneOne and PLS (see Note 12 for additional information about the Company’s investments in these affiliated entities).

Level 2 assets at December 31, 2017 and 2016 consisted of US corporate debt securities and mutual funds held by the Company that are initially valued at the transaction price and subsequently valued, at the end of each reporting period, typically utilizing market observable data. The Company obtains the fair value of its Level 2 assets from a professional pricing service, which may use quoted market prices for identical or comparable instruments, or inputs other than quoted prices that are observable either directly or indirectly. The professional pricing service gathers quoted market prices and observable inputs from a variety of industry data providers. The valuation techniques used to measure the fair value of the Company's Level 2 financial instruments were derived from non-binding market consensus prices that are corroborated by observable market data, quoted market prices for similar instruments, or pricing models such as discounted cash flow techniques. The Company validates the quoted market prices provided by the primary pricing service by comparing their assessment of the fair values of the Company's investment portfolio balance against the fair values of the Company's investment portfolio balance obtained from an independent source.

There were no Level 3 assets held as of December 31, 2017. Level 3 assets held at December 31, 2016 consisted of a warrant received by the Company in 2012 to purchase shares of common stock of OncoSec Medical Incorporated (“OncoSec”). This warrant expired unexercised in March 2017 and was considered to have zero value as of December 31, 2016. Another warrant to purchase shares of common stock of OncoSec held by the Company expired unexercised in September 2016.

The Company recorded a change in fair value of the OncoSec warrants of $0, $(6,000) and $(544,000) for the years ended December 31, 2017, 2016 and 2015, respectively. The change in fair value is reflected in the Company's consolidated statement of operations as a component of change in fair value of common stock warrants.

Level 3 liabilities held as of December 31, 2017 and 2016 consisted of common stock warrant liabilities associated with warrants to purchase the Company's common stock issued in March 2013. If unexercised, the warrants will expire in September 2018. During the years ended December 31, 2017 and 2016, none of these warrants were exercised. See Note 10 for additional information about the warrants.

As of December 31, 2017 the Company had a $361,000 common stock warrant liability. The Company reassesses the fair value of the common stock warrants at each reporting date utilizing a Black-Scholes pricing model. Inputs used in the pricing model include estimates of stock price volatility, expected warrant life and risk-free interest rate. The Company develops its estimates based on historical data. The assumptions used to estimate the fair value of common stock warrants at December 31, 2017 and 2016 are presented below:



	Year Ended December 31,
	2017	2016
Risk-free interest rate	1.75%	1.1%
Expected volatility	55%	61%
Expected life in years	0.70	1.70
Dividend yield	—	—

Changes in these assumptions as well as fluctuations in the Company's stock price between the valuation dates can have a significant impact on the fair value of the common stock warrant liability. As a result of these calculations, the Company recorded a decrease in fair value of $(807,000), $(134,000) and $(722,000) for the years ended December 31, 2017, 2016 and 2015, respectively. The change in fair value is reflected in the Company's consolidated statement of operations as a component of change in fair value of common stock warrants.

The following table presents the changes in fair value of the Company’s total Level 3 financial liabilities for the years ended December 31, 2017 and 2016:



	Year Ended December 31,
	2017			2016
Balance at beginning of year	$	1,167,614		$	1,301,138
Decrease in fair value included in change in fair value of common stock warrants	(806,819		)	(133,524		)
Balance at end of year	$	360,795		$	1,167,614