Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2021

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, 2021
Available-for-sale securities:
Corporate bonds and notes	$	1,434	$	8	$	(2	)	$	1,440
Municipal bonds		1,573		—		(3	)		1,570
Total available-for-sale securities	$	3,007		8		(5	)		3,010
December 31, 2020
Available-for-sale securities:
Corporate bonds and notes	$	1,312	$	26	$	—		$	1,338
Municipal bonds		1,536		5		—			1,541
Total available-for-sale securities	$	2,848	$	31	$	—		$	2,879

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

	Amortized		Estimated
	cost		fair value
Due within one year	$	1,785	$	1,791
Due after one year through five years		1,222		1,219
Total available-for-sale securities	$	3,007	$	3,010