Fair Value Measurements (Financial Assets measured at Fair Value on a Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	$ 15,290	$ 19,889
Level 1 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	14,602	16,089
Level 2 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	688	3,800
Level 3 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	0	0
Money Market Funds [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	14,602	16,089
Money Market Funds [Member] | Level 1 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	14,602	16,089
Money Market Funds [Member] | Level 2 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	0	0
Money Market Funds [Member] | Level 3 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	0	0
Corporate Bonds [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis		1,005
Corporate Bonds [Member] | Level 1 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis		0
Corporate Bonds [Member] | Level 2 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis		1,005
Corporate Bonds [Member] | Level 3 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis		0
U.S. Treasury Obligations [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis		2,000
U.S. Treasury Obligations [Member] | Level 1 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis		0
U.S. Treasury Obligations [Member] | Level 2 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis		2,000
U.S. Treasury Obligations [Member] | Level 3 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis		0
Common Shares of CO2 Solutions [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	688	795
Common Shares of CO2 Solutions [Member] | Level 1 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis		0
Common Shares of CO2 Solutions [Member] | Level 2 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	688	795
Common Shares of CO2 Solutions [Member] | Level 3 [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	$ 0	$ 0