We measure certain financial assets and liabilities at fair value. Fair value is determined based upon the exit price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants, as determined by either the principal market or the most advantageous market. Inputs used in the valuation techniques to derive fair values are classified based on a three-level hierarchy, as follows:

Level 1: Observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets.

Level 2: Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities; quoted prices in markets with insufficient volume or infrequent transactions (less active markets); or model-derived valuations in which all significant inputs are observable or can be derived principally from or corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the asset or liability.

We consider an active market to be one in which transactions for the asset or liability occur with sufficient frequency and volume to provide pricing information on an ongoing basis, and we consider an inactive market to be one in which there are infrequent or few transactions for the asset or liability, the prices are not current, or price quotations vary substantially either over time or among market makers.

The following table presents our financial assets measured and recorded at fair value on a recurring basis using the above input categories:


	As of September 30, 2020
	Level 1		Level 2		Level 3		Total
	(in thousands)
Description:
Assets:
Money market funds	$	215,449	$	—	$	—	$	215,449
U.S. government agencies	32,987		—		—		32,987
Commercial paper	—		32,252		—		32,252
Corporate bonds	—		20,349		—		20,349
Agency bonds	—		3,998		—		3,998
Asset-backed securities	—		2,436		—		2,436
Total assets	$	248,436	$	59,035	$	—	$	307,471
Liabilities:
Foreign currency forward contracts designated as cash flow hedges	$	—	$	88	$	—	$	88
Total liabilities	$	—	$	88	$	—	$	88


	As of December 31, 2019
	Level 1		Level 2		Level 3		Total
	(in thousands)
Description:
Assets:
Money market funds	$	106,781	$	—	$	—	$	106,781
Corporate bonds	—		60,878		—		60,878
U.S. government agencies	36,979		—		—		36,979
Commercial paper	—		19,966		—		19,966
Agency bonds	—		12,242		—		12,242
Asset-backed securities	—		8,980		—		8,980
Total assets	$	143,760	$	102,066	$	—	$	245,826

As of September 30, 2020, the fair values of our 1.25% and 2.25% convertible senior notes due 2023 and 2025, respectively, as further described in Note 9, Debt, were $359.5 million and $289.2 million, respectively, based upon quoted market prices. We consider the fair values of the convertible senior notes to be a Level 2 measurement due to the limited trading activity of both notes. We had no other liabilities measured and recorded at fair value on a recurring basis as of September 30, 2020 or December 31, 2019.


	As of September 30, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
	(in thousands)
Description:
U.S. government agencies	32,984		3		—		32,987
Commercial paper	32,252		—		—		32,252
Corporate bonds	20,287		69		(7)		20,349
Agency bonds	3,998		—		—		3,998
Asset-backed securities	2,436		—		—		2,436
Total assets	$	91,957	$	72	$	(7)	$	92,022


	As of December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
	(in thousands)
Description:
U.S. government agencies	$	36,880	$	99	$	—	$	36,979
Corporate bonds	60,803		77		(2)		60,878
Commercial paper	19,965		1		—		19,966
Agency bonds	12,198		44		—		12,242
Asset-backed securities	8,986		1		(7)		8,980
Total assets	$	138,832	$	222	$	(9)	$	139,045

As of September 30, 2020, our available-for-sale investments had maturities ranging from one to nineteen months. As of December 31, 2019, our available-for-sale investments had maturities ranging from three months to two years.