Marketable Securities (Components of Cash Equivalents and Marketable Securities) (Details) $ in Thousands	Sep. 30, 2015 USD ($) security	Dec. 31, 2014 USD ($) security
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	$ 11,678	$ 15,165
Gross Unrealized Gains	668	125
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 12,346	$ 15,290
Number of Marketable Securities In Unrealized Loss Position | security	0	0
Money market funds [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	$ 11,115	$ 14,602
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	11,115	14,602
Common shares of CO2 Solution [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	563	563
Gross Unrealized Gains	668	125
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 1,231	$ 688