Investments

As of March 31, 2020 and December 31, 2019, the Company primarily invested its excess cash in debt instruments of corporations, the U.S. Treasury, financial institutions, and U.S. government agencies with strong credit ratings and an investment grade rating at or above a long-term rating of Aa3/AA- and a short-term rating of P1/A1. The Company has established guidelines relative to diversification and maturities that maintain safety and liquidity. The Company periodically reviews and modifies these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity.

The following table summarizes the contract maturity of the available-for-sale securities the Company held as of March 31, 2020:



One year or less	64	%
After one year but within two years	36	%
Total	100	%

All of the Company’s available-for-sale securities are available to the Company for use in its current operations. As a result, the Company categorizes all of these securities as current assets even though the stated maturity of some individual securities may be one year or more beyond the balance sheet date.

The amortized cost, gross unrealized holding gains, gross unrealized holding losses and fair value of cash equivalents and available-for-sale securities by type of security at March 31, 2020 and December 31, 2019 were as follows:



	March 31, 2020
	Amortized Costs		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
Commercial paper	$	10,718	$	3	$	(9	)	$	10,712
Corporate notes/bonds	49,973		44		(158		)	49,859
U.S. Treasuries	4,510		36		—			4,546
U.S. Government agency securities	9,039		67		—			9,106
	$	74,240	$	150	$	(167	)	$	74,223



	December 31, 2019
	Amortized Costs		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
Commercial paper	$	13,932	$	1	$	(2	)	$	13,931
Corporate notes/bonds	36,620		1		(24		)	36,597
U.S. Treasuries	4,513		—		(1		)	4,512
U.S. Government agency securities	9,786		—		(2		)	9,784
	$	64,851	$	2	$	(29	)	$	64,824