The following is a summary of our available-for-sale debt securities recorded within short-term and long-term investments on the condensed consolidated balance sheets (in thousands):


	June 30, 2020
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-sale securities:
Commercial paper	$	414,613	$	521	$	(31)	$	415,103
Corporate notes and bonds	1,571,083		15,645		(493)		1,586,235
Certificates of deposit	20,077		21		—		20,098
U.S. government and agency securities	259,097		1,641		(5)		260,733

Total available-for-sale securities	$	2,264,870	$	17,828	$	(529)	$	2,282,169


	December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Available-for-sale securities:
Commercial paper	$	101,416	$	83	$	(9)	$	101,490
Corporate notes and bonds	1,654,166		7,360		(196)		1,661,330
Certificates of deposit	38,007		38		—		38,045
U.S. government and agency securities	127,544		254		(14)		127,784
Total available-for-sale securities	$	1,921,133	$	7,735	$	(219)	$	1,928,649

As of June 30, 2020, the contractual maturities of our available-for-sale debt securities, excluding those securities classified within cash and cash equivalents on the condensed consolidated balance sheet, did not exceed 36 months. The fair values of available-for-sale securities, by remaining contractual maturity, are as follows (in thousands):

The following table shows the fair values and the gross unrealized losses of these available-for-sale debt securities, classified by the length of time that the securities have been in a continuous unrealized loss position, and aggregated by investment types, excluding those securities classified within cash and cash equivalents on the condensed consolidated balance sheets (in thousands):


	June 30, 2020
	Less than 12 Months						12 Months or Greater						Total
	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Commercial paper	$	82,317	$	(31)	$	—	$	—	$	82,317	$	(31)
Corporate notes and bonds	273,570		(493)		—		—		273,570		(493)

U.S. government and agency securities	72,843		(5)		—		—		72,843		(5)
Total	$	428,730	$	(529)	$	—	$	—	$	428,730	$	(529)


	December 31, 2019
	Less than 12 Months						12 Months or Greater						Total
	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Commercial paper	$	20,752	$	(9)	$	—	$	—	$	20,752	$	(9)
Corporate notes and bonds	242,012		(181)		16,264		(15)		258,276		(196)

U.S. government and agency securities	17,806		(14)		—		—		17,806		(14)
Total	$	280,570	$	(204)	$	16,264	$	(15)	$	296,834	$	(219)

The decline in fair value below amortized cost basis was not considered other than temporary as it is more likely than not we will hold the securities until maturity or a recovery of the cost basis, and credit-related impairment losses were not deemed material as of June 30, 2020.

As of June 30, 2020 and December 31, 2019, the total amount of equity investments in privately-held companies included in other assets on our condensed consolidated balance sheets was $27 million and $22 million, respectively. We classify these assets as Level 3 within the fair value hierarchy only if an impairment or observable adjustment is recognized on these non-marketable equity securities during the period as they are based on observable transaction price at the transaction date of identical or similar investment of the same issuer and other unobservable inputs such as volatility.