Cash Equivalents and Marketable Securities (Components of Cash Equivalents and Marketable Securities) (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	$ 24,646,000	$ 41,873,000
Gross Unrealized Gains	509,000	63,000
Gross Unrealized Losses	0	0
Estimated Fair Value	25,155,000	41,936,000
Money market funds [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	21,079,000	24,789,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	21,079,000	24,789,000
Commercial paper [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost		1,499,000
Gross Unrealized Gains		1,000
Gross Unrealized Losses		0
Estimated Fair Value		1,500,000
Average Contractual Maturities (in days)		70 days
Corporate bonds (unamortized cost) [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	1,004,000	9,512,000
Gross Unrealized Gains	3,000	10,000
Gross Unrealized Losses	0	0
Estimated Fair Value	1,007,000	9,522,000
Average Contractual Maturities (in days)	151 days	156 days
U.S. Treasury obligations (unamortized cost) [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	2,000,000	5,510,000
Gross Unrealized Gains	2,000	5,000
Gross Unrealized Losses	0	0
Estimated Fair Value	2,002,000	5,515,000
Average Contractual Maturities (in days)	232 days	262 days
Common shares of CO2 Solution [Member]
Cash Equivalents and Marketable Securities [Line Items]
Adjusted Cost	563,000	563,000
Gross Unrealized Gains	504,000	47,000
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 1,067,000	$ 610,000