Marketable Securities (Components of Cash Equivalents and Marketable Securities) (Details) $ in Thousands	Jun. 30, 2015 USD ($) securities	Dec. 31, 2014 USD ($)
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	$ 13,175	$ 15,165
Gross Unrealized Gains	1,379	125
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 14,554	15,290
Number of Marketable Securities | securities	0
Money market funds [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	$ 12,612	14,602
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	12,612	14,602
Common shares of CO2 Solution [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	563	563
Gross Unrealized Gains	1,379	125
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 1,942	$ 688