Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2019

Marketable Securities

Schedule of amortized cost, gross unrealized holding gains, gross unrealized holding losses, and fair value for available-for-sale securities by major security type and class of security

	Amortized cost		Gross unrealized holding gains		Gross unrealized holding losses			Estimated fair value
December 31, 2019
Available-for-sale securities:
Corporate bonds and notes	$	1,814		21		(3	)		1,832
Municipal bonds		2,707		5		(1	)		2,711
Total available-for-sale securities	$	4,521		26		(4	)		4,543
December 31, 2018
Available-for-sale securities:
Corporate bonds and notes	$	2,911	$	1	$	(31	)	$	2,881
Municipal bonds		1,849		—		(15	)		1,834
Total available-for-sale securities	$	4,760	$	1	$	(46	)	$	4,715

Schedule of maturities of marketable securities classified as available-for-sale securities

	Amortized		Estimated
	cost		fair value
Due within one year	$	3,021		3,026
Due after one year through five years		1,500		1,517
Total available-for-sale securities	$	4,521		4,543

Schedule of available-for-sale marketable securities in a gross unrealized loss position

	Less than 12 months				More than 12 months				Total
	Estimated fair value		Gross unrealized holding losses		Estimated fair value		Gross unrealized holding losses		Estimated fair value		Gross unrealized holding losses
As of December 31, 2019
Corporate bonds and notes	$	194	$	3	$	—	$	—	$	194	$	3
Municipal bonds		2,003		1		—		—		2,003		1
	$	2,197	$	4	$	-	$	-	$	2,197	$	4