Marketable Securities

3 Months Ended

Mar. 31, 2020

Marketable Securities

Marketable Securities

4.  Marketable Securities

Marketable securities consist of the following:

	March 31, 2020
			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated
(in thousands)	Cost		Gain		Loss		Fair Value
Agency bonds	$	35,643	$	157	$	—	$	35,800
Corporate bonds		258,091		186		(886)		257,391
Total	$	293,734	$	343	$	(886)	$	293,191

	December 31, 2019
			Gross		Gross
	Amortized		Unrealized		Unrealized		Estimated
(in thousands)	Cost		Gain		Loss		Fair Value
U.S. treasury securities	$	4,991	$	—	$	—	$	4,991
Agency bonds		24,437		15		(1)		24,451
Corporate bonds		271,124		103		(155)		271,072
Total	$	300,552	$	118	$	(156)	$	300,514

As of March 31, 2020, no marketable securities are considered to be other-than-temporarily impaired. The Company uses the specific identification method when calculating realized gains and losses. For the three months ended March 31, 2020, the Company recorded approximately $64,000 in realized gains on available-for-sale securities.