Cash and Cash Equivalents and Investments (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash and Cash Equivalents
Realized Investment Gains (Losses)	$ 0	$ 0	$ 0
Cash
Cash and Cash Equivalents
Available-for-sale Securities, Amortized Cost Basis	37,499,000	30,423,000
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities, Current	37,499,000	30,423,000
Certificates of Deposit
Cash and Cash Equivalents
Available-for-sale Securities, Amortized Cost Basis	552,000	551,000
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	0	0
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities, Current	552,000	551,000
US Treasury Securities
Cash and Cash Equivalents
Available-for-sale Securities, Amortized Cost Basis	91,075,000	192,211,000
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	3,000	24,000
Available-for-sale Securities, Gross Unrealized Losses	(1,000)	(1,000)
Available-for-sale Securities, Current	91,077,000	192,234,000
Short-term Investments
Cash and Cash Equivalents
Available-for-sale Securities, Amortized Cost Basis	91,627,000	192,762,000
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	3,000	24,000
Available-for-sale Securities, Gross Unrealized Losses	(1,000)	(1,000)
Available-for-sale Securities, Current	91,629,000	192,785,000
Cash and Cash Equivalents and Investments
Cash and Cash Equivalents
Available-for-sale Securities, Amortized Cost Basis	129,126,000	223,185,000
Available-for-sale Securities, Gross Unrealized Gain Accumulated in Investments	3,000	24,000
Available-for-sale Securities, Gross Unrealized Losses	(1,000)	(1,000)
Available-for-sale Securities, Current	$ 129,128,000	$ 223,208,000