Cash Equivalents and Marketable Securities (Components of Cash Equivalents and Marketable Securities) (Details) $ in Thousands	Jun. 30, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	$ 11,704	$ 11,683
Gross Unrealized Gains	552	986
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 12,256	$ 12,669
Number of Marketable Securities In Unrealized Loss Position | security	0	0
Money market funds [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	$ 11,141	$ 11,120
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	11,141	11,120
Common shares of CO2 Solution [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	563	563
Gross Unrealized Gains	552	986
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 1,115	$ 1,549