Cash Equivalents and Marketable Securities (Components of Cash Equivalents and Marketable Securities) (Details) $ in Thousands	Mar. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	$ 11,753	$ 11,735
Gross Unrealized Gains	488	579
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 12,241	$ 12,314
Number of Marketable Securities In Unrealized Loss Position | security	0	0
Common shares of CO2 Solution [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	$ 563	$ 563
Gross Unrealized Gains	488	579
Gross Unrealized Losses	0	0
Estimated Fair Value	1,051	1,142
Money Market Funds [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	11,190	11,172
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 11,190	$ 11,172