Cash, Money Market Funds and Marketable Securities (Details) (USD $)	12 Months Ended										143 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007	Dec. 31, 2006	Dec. 31, 2005	Dec. 31, 2004	Dec. 31, 2013
Cash, Money Market Funds, and Marketable Securities
Cash and cash equivalents, Amortized Cost	$ 43,640,000	$ 33,971,000	$ 25,668,000	$ 29,572,000							$ 43,640,000
Cash and cash equivalents, Fair Value	43,640,000	33,971,000									43,640,000
Marketable securities, Amortized Cost	38,359,000	65,137,000									38,359,000
Unrealized Gain	7,000	25,000									7,000
Unrealized Loss	(6,000)	(11,000)									(6,000)
Marketable securities, Fair Value	38,360,000	65,151,000									38,360,000
Cash and marketable securities, Amortized Cost	81,999,000	99,108,000									81,999,000
Cash and marketable securities, Fair Value	82,000,000	99,122,000									82,000,000
Available-for-sale investments
Realized gain (loss) on securities available-for-sale	0	0
Fair value of available for sale securities in unrealized loss positions	23,600,000	33,100,000									23,600,000
Changes in AOCI associated with the unrealized holding gain on available-for-sale investments
Balance, beginning	14,000	4,000
Current period changes in fair value	(13,000)	10,000	32,000	(71,000)	(490,000)	125,000	393,000	31,000	(7,000)	(9,000)	1,000
Balance, ending	1,000	14,000	4,000								1,000
Corporate debt securities
Cash, Money Market Funds, and Marketable Securities
Marketable securities, Amortized Cost	30,817,000	42,503,000									30,817,000
Unrealized Gain	1,000	5,000									1,000
Unrealized Loss	(6,000)	(11,000)									(6,000)
Marketable securities, Fair Value	30,812,000	42,497,000									30,812,000
Commercial paper
Cash, Money Market Funds, and Marketable Securities
Marketable securities, Amortized Cost	7,192,000	19,725,000									7,192,000
Unrealized Gain	6,000	19,000									6,000
Marketable securities, Fair Value	7,198,000	19,744,000									7,198,000
Certificate of deposit
Cash, Money Market Funds, and Marketable Securities
Marketable securities, Amortized Cost	350,000	2,909,000									350,000
Unrealized Gain		1,000
Marketable securities, Fair Value	$ 350,000	$ 2,910,000									$ 350,000