4. Investments

The following is a summary of investments as of June 30, 2018 and December 31, 2017. The Company considered all investments as available for sale.


	As of June 30, 2018
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
Municipal securities	$	76,783	$	2	$	(263	)	$	76,522

Total investments	$	76,783	$	2	$	(263	)	$	76,522


	As of December 31, 2017
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
Municipal securities	$	84,768	$	—	$	(409	)	$	84,359
Certificates of Deposit	$	4,915	$	—	$	(3	)	$	4,912

Total investments	$	89,683	$	—	$	(412	)	$	89,271

The cash flows of municipal securities are backed by the issuing municipality’s credit worthiness. All municipal securities are due in one year or less as of June 30, 2018. For the six months ended June 30, 2018, the net unrealized losses on available-for-sale securities was $196, net of taxes.