Cash Equivalents and Marketable Securities (Components of Cash Equivalents and Marketable Securities) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	$ 16,156	$ 19,654
Gross Unrealized Gains	884	235
Gross Unrealized Losses	0	0
Estimated Fair Value	17,040	19,889
Money market funds [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	14,592	16,089
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	14,592	16,089
Corporate bonds (unamortized cost) [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	1,001	1,002
Gross Unrealized Gains	1	3
Gross Unrealized Losses	0	0
Estimated Fair Value	1,002	1,005
Average Contractual Maturities (in days)	50 days	140 days
U.S. Treasury obligations (unamortized cost) [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost		2,000
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Estimated Fair Value		2,000
Average Contractual Maturities (in days)		59 days
Common shares of CO2 Solution [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	563	563
Gross Unrealized Gains	883	232
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 1,446	$ 795