- Narrative (Details) - USD ($)	1 Months Ended
	Dec. 31, 2009	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents		$ 31,219,000	$ 19,240,000	$ 23,273,000	$ 26,487,000
Money market funds		6,800,000	11,200,000
Cash		24,400,000	8,068,000
Initial ownership percentage at the time of investment	16.60%
Statutory resale restriction expiry period	4 months
Number of marketable securities in unrealized loss position		$ 0	$ 0
Common shares of CO2 Solutions
Schedule of Available-for-sale Securities [Line Items]
Number of CO2 Solutions common shares we invested in (shares)	10,000,000