Marketable Securities (Details) (USD $)	Dec. 31, 2012 item	Dec. 31, 2011 item	Dec. 31, 2010	Dec. 31, 2009
Available-for-sale marketable securities
Cash and cash equivalents, Carrying Value	$ 18,653,000	$ 25,128,000	$ 10,582,000	$ 7,896,000
Cash and cash equivalents, Fair Value	18,653,000	25,128,000
Marketable securities, Amortized Cost	4,000,000	31,575,000
Marketable securities, Gross Unrealized Gains		11,000
Marketable securities, Gross Unrealized Losses		(6,000)
Marketable securities, Fair Value	4,000,000	31,580,000
Debt securities held in an unrealized position for more than 12 months	0	0
Debt securities held in an unrealized position for less than 12 months	0	7
Unrealized loss on debt securities in an unrealized loss position for less than 12 months		6,000
Fair value of debt securities in an unrealized position for less than 12 months		8,000,000
Domestic corporate debt securities
Available-for-sale marketable securities
Marketable securities, Amortized Cost		10,260,000
Marketable securities, Gross Unrealized Losses		(6,000)
Marketable securities, Fair Value		10,254,000
Domestic corporate commercial paper
Available-for-sale marketable securities
Marketable securities, Amortized Cost	4,000,000	18,987,000
Marketable securities, Gross Unrealized Gains		11,000
Marketable securities, Fair Value	4,000,000	18,998,000
U.S Government Securities
Available-for-sale marketable securities
Marketable securities, Amortized Cost		2,328,000
Marketable securities, Fair Value		2,328,000
Cash
Available-for-sale marketable securities
Cash and cash equivalents, Carrying Value	1,134,000	5,003,000
Cash and cash equivalents, Fair Value	1,134,000	5,003,000
Money market
Available-for-sale marketable securities
Cash and cash equivalents, Carrying Value	16,020,000	20,125,000
Cash and cash equivalents, Fair Value	16,020,000	20,125,000
Domestic corporate commercial paper
Available-for-sale marketable securities
Cash and cash equivalents, Carrying Value	1,499,000
Cash and cash equivalents, Fair Value	$ 1,499,000