Cash, Cash Equivalents and Short-term Investments (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash, cash equivalents and marketable securities
Cash and money market funds, Amortized Cost	$ 6,414,000	$ 18,078,000
Cash and money market funds, Fair Value	6,414,000	18,078,000
Amortized Cost	60,257,000	44,417,000
Gross Unrealized Gains	2,000	13,000
Gross Unrealized Losses	(28,000)	(3,000)
Fair Value	60,231,000	44,427,000
Amortized cost of cash and cash equivalents	6,414,000	18,078,000	14,776,000	4,541,000
Fair value of cash and cash equivalents	6,414,000	18,078,000
Amortized cost of cash and cash equivalents and marketable securities	60,257,000	44,417,000
Fair value of cash and cash equivalents and marketable securities	60,231,000	44,427,000
Number of debt securities that had been in an unrealized loss position for less than 12 months	32	8
Number of debt securities that had been in an unrealized loss position for 12 months or longer	0	0
Fair value of debt securities that had been in an unrealized loss position for less than 12 months	44,200,000	9,500,000
Corporate debt securities due in one year or less
Cash, cash equivalents and marketable securities
Amortized Cost	53,843,000	22,631,000
Gross Unrealized Gains	2,000	11,000
Gross Unrealized Losses	(28,000)	(2,000)
Fair Value	53,817,000	22,640,000
Corporate debt securities due in two years or less
Cash, cash equivalents and marketable securities
Amortized Cost		3,708,000
Gross Unrealized Gains		2,000
Gross Unrealized Losses		(1,000)
Fair Value		3,709,000
Short-term investments Member
Cash, cash equivalents and marketable securities
Amortized Cost	53,843,000	26,339,000
Gross Unrealized Gains	2,000	13,000
Gross Unrealized Losses	(28,000)	(3,000)
Fair Value	53,817,000	26,349,000
Realized gains	0	0	0
Realized losses	0	0	0
Other-than-temporary impairments recognized	0	0	0
Financial institution debt securities and other corporate debt securities located in foreign countries
Cash, cash equivalents and marketable securities
Amortized Cost	$ 7,500,000	$ 11,700,000