Cash Equivalents and Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

Cash equivalents and marketable securities classified as available-for-sale at December 31, 2017 and 2016 consisted of the following (in thousands):



	December 31, 2017
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value		Average Contractual Maturities
									(in days)
Money market funds ⁽¹⁾	$	6,778	$	—	$	—	$	6,778	n/a
Common shares of CO₂ Solutions ⁽²⁾	563		108		—		671		n/a
Total	$	7,341	$	108	$	—	$	7,449



	December 31, 2016
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value		Average Contractual Maturities
									(in days)
Money market funds ⁽¹⁾	$	11,172	$	—	$	—	$	11,172	n/a
Common shares of CO₂ Solutions ⁽²⁾	563		579		—		1,142		n/a
Total	$	11,735	$	579	$	—	$	12,314

⁽¹⁾Money market funds are classified in cash and cash equivalents on our consolidated balance sheets.

⁽²⁾Common shares of CO₂ Solutions are classified in marketable securities on our consolidated balance sheets.