5. Investments

Investments in Privately-Held Companies

Our investments are in the equity of privately-held companies, which do not have readily determinable fair values. The following tables summarize activities related to our investments in privately-held companies during the three months ended March 31, 2019 and 2018 (in thousands):



	Three Months Ended March 31, 2019
	Cost of Investments		Cumulative Downward Adjustment/ Impairment			Cumulative Upward Adjustment		Carrying Amount
Balance of investments held at the beginning of the period	$	44,136	$	(15,000	)	$	1,200	$	30,336
Additions	—		—			1,150		1,150
Balance of investments held at the end of the period	$	44,136	$	(15,000	)	$	2,350	$	31,486



	Three Months Ended March 31, 2018
	Cost of Investments		Cumulative Downward Adjustment/ Impairment		Cumulative Upward Adjustment		Carrying Amount
Balance of investments held at the beginning of the period	$	36,136	$	—	$	—	$	36,136
Additions	—		—		—		—
Balance of investments held at the end of the period	$	36,136	$	—	$	—	$	36,136

As of March 31, 2019 and December 31, 2018, the carrying amount of the investments that have been remeasured to fair value as a result of impairment or observable transactions totaled $26.5 million and $22.3 million, respectively, and are classified within Level III of the fair value hierarchy.