Investments

6 Months Ended

Jun. 30, 2020

Investments Debt And Equity Securities [Abstract]

Investments

5. Investments

Available-for-sale investments consisted of the following as of June 30, 2020 and December 31, 2019 (in thousands):

	June 30, 2020
	Amortized Cost		Unrealized Gain		Unrealized Loss		Estimated Fair Value
Short-term marketable securities
Commercial paper	$	5,994	$	—	$	—	$	5,994
U.S. government debt and agency securities		195,764		1,167		—		196,931
Corporate bonds		2,007		8		—		2,015
Total short-term marketable securities	$	203,765	$	1,175	$	—	$	204,940
Long-term marketable securities
U.S. government debt and agency securities	$	46,436	$	810	$	—	$	47,246
Corporate bonds		9,969		168		—		10,137
Total long-term marketable securities	$	56,405	$	978	$	—	$	57,383

	December 31, 2019
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
Short-term marketable securities
Commercial paper	$	121,866	$	—	$	—		$	121,866
U.S. government debt and agency securities		285,963		394		(1	)		286,356
Corporate bonds		71,962		109		(3	)		72,068
Total short-term marketable securities	$	479,791	$	503	$	(4	)	$	480,290
Long-term marketable securities
U.S. government debt and agency securities	$	90,750	$	146	$	(9	)	$	90,887
Corporate bonds		14,513		35		—			14,548
Total long-term marketable securities	$	105,263	$	181	$	(9	)	$	105,435

All the commercial paper, U.S. government debt and agency securities and corporate bonds designated as short-term marketable securities have an effective maturity date that is equal to or less than one year from the respective balance sheet date. Those that are designated as long-term marketable securities have an effective maturity date that is more than one year from the respective balance sheet date.

Accrued interest receivable is excluded from the amortized cost and estimated fair value of our marketable securities. Accrued interest receivables of $1.5 million and $2.2 million were presented separately within the prepaid expenses and other current assets line item on our unaudited condensed balance sheet as of June 30, 2020 and our balance sheet as of December 31, 2019, respectively. We have made an accounting policy election to not measure an allowance for credit losses for accrued interest receivables.

We periodically review our available-for-sale securities to assess for credit impairment. Some of the factors considered in assessing impairment include the extent to which the fair value is less than the amortized cost basis, adverse conditions related to the security, an industry or geographic area, changes to security ratings or sector credit ratings and other relevant market data. As of June 30, 2020, none of our investments were in an unrealized loss position and, based on our assessment, none exhibited credit impairment. As such, a credit allowance was not recognized. Furthermore, as of June 30, 2020, we did not intend, nor were we more likely than not to be required, to sell our available-for-sale investments before the recovery of their amortized cost basis.