Fair Value Measurements (Schedule of Financial Instruments Measured at Fair Value on Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Held-for-sale, at Carrying Value	$ 1,394	$ 2,179
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	17,040	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	14,592	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	2,448	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	14,592	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	14,592	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	1,002	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	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	1,002	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	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 Solution [Member]
Summary of financial instruments measured at fair value on a recurring basis
Total financial assets measured at fair value on a recurring basis	1,446	795
Common shares of CO2 Solution [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	0
Common shares of CO2 Solution [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	1,446	795
Common shares of CO2 Solution [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
Assets Held-for-sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Held-for-sale, at Carrying Value	1,394	2,179
Assets Held-for-sale [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Held-for-sale, at Carrying Value	0	0
Assets Held-for-sale [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Held-for-sale, at Carrying Value	0	0
Assets Held-for-sale [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Held-for-sale, at Carrying Value	$ 1,394	$ 2,179