4.Fair Value Measurements

The fair value of the Company’s financial instruments reflects the amounts that the Company estimates it would receive in connection with the sale of an asset or pay in connection with the transfer of a liability in an orderly transaction between market participants at the measurement date (exit price). The Company discloses and recognizes the fair value of its assets and liabilities using a hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to valuations based upon unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to valuations based upon unobservable inputs that are significant to the valuation (Level 3 measurements). The guidance establishes three levels of the fair value hierarchy as follows:

Level 1 – Inputs that reflect unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date;

Level 2 – Inputs other than quoted prices that are observable for the assets or liability either directly or indirectly, including inputs in markets that are not considered to be active;

Level 3 – Inputs that are unobservable.

Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability.

During the periods presented, the Company has not changed the manner in which it values assets and liabilities that are measured at fair value using Level 3 inputs. The Company recognizes transfers between levels of the fair value hierarchy as of the end of the reporting period. There were no transfers within the hierarchy during the periods presented. A summary of the assets and liabilities carried at fair value in accordance with the hierarchy defined above is as follows (in thousands):

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
September 30, 2018 (unaudited)
Assets:
Money market funds	$	9,850	$	—	$	—	$	9,850
Corporate notes		—		31,694		—		31,694
Commercial paper		—		83,744		—		83,744
Asset backed securities		—		12,198		—		12,198
Government notes		—		12,430		—		12,430
Total assets	$	9,850	$	140,066		—	$	149,916

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
December 31, 2017:
Assets:
Money market funds	$	8,685	$	—	$	—	$	8,685
Corporate notes		5,103		40,995		—		46,098
Government notes		6,175		—		—		6,175
Total assets	$	19,963	$	40,995	$	—	$	60,958

The Company uses a market approach for determining the fair value of all its Level 1 and Level 2 money market funds and marketable securities. To value its money market funds, the Company values the funds at $1 stable net asset value, which is the market pricing convention for identical assets that the Company has the ability to access.