4. Fair value measurements

The following table presents information about the Company's assets and liabilities regularly measured and carried at a fair value and indicates the level within fair value hierarchy of the valuation techniques utilized to determine such value as of September 30, 2019 and December 31, 2018:


					Significant
			Quoted Prices		Other		Significant
			in Active		Observable		Unobservable
	Fair		Markets		Inputs		Inputs
	Value		(Level 1)		(Level 2)		(Level 3)
September 30, 2019
Marketable securities:
Commercial paper	$	14,871	$	—	$	14,871	$	—
Corporate bonds		12,010		—		12,010		—
U.S. Treasuries		26,925		—		26,925		—
	$	53,806	$	—	$	53,806	$	—


					Significant
			Quoted Prices		Other		Significant
			in Active		Observable		Unobservable
	Fair		Markets		Inputs		Inputs
	Value		(Level 1)		(Level 2)		(Level 3)
December 31, 2018
Marketable securities:
U.S. Treasuries	$	10,497	$	10,497	$	—	$	—
	$	10,497	$	10,497	$	—	$	—

The carrying amounts of accounts payable and accrued expenses approximate their fair values due to their short-term maturities. There were no changes in valuation techniques or transfers between fair value measurement levels during the nine months ended September 30, 2019 and 2018. As of September 30, 2019, and December 31, 2018, cash and cash equivalents were comprised of cash and money market funds.

There were no changes in valuation techniques or transfers between fair value measurement levels during the nine months ended September 30, 2019 and 2018.

Cash and Cash Equivalents

The carrying amounts of accounts payable and accrued expenses approximate their fair values due to their short-term maturities. As of September 30, 2019, and December 31, 2018, cash and cash equivalents were comprised of cash and money market funds.

Marketable Securities

Marketable securities classified as Level 2 within the valuation hierarchy generally consist of U.S. treasury securities, corporate bonds and commercial paper. The Company estimates the fair values of these marketable securities by taking into consideration valuations obtained from third-party pricing sources. These inputs include market pricing based on real-time trade data for the same or similar securities, issuer credit spreads, benchmark yields and other observable inputs. The Company validates the prices provided by its third-party pricing sources by obtaining market values from other pricing sources and analyzing pricing data in certain instances. As of September 30, 2019, the carrying value of the Company’s outstanding borrowing under the Credit Facility approximates fair value (a Level 2 fair value measurement), reflecting interest rates currently available to the Company. The Credit Facility is discussed more detail in Note 7, “Debt”.