Summary of Significant Accounting Policies (Details 2) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013 item	Sep. 30, 2013 item
Available-for-sale securities
Realized gains (losses) recognized on the sale or maturity of securities	$ 0	$ 0
Number of securities in unrealized loss position for less than 12 months	13	13
Aggregate Fair Value	59,072,000	59,072,000
Unrealized Losses	(25,000)	(25,000)
Amortized Cost	77,050,000	77,050,000
Unrealized Gains	9,000	9,000
Unrealized Losses	(25,000)	(25,000)
Fair Value	77,034,000	77,034,000
Certificate of deposit
Available-for-sale securities
Amortized Cost	960,000	960,000
Fair Value	960,000	960,000
Commercial paper
Available-for-sale securities
Aggregate Fair Value	18,485,000	18,485,000
Unrealized Losses	(5,000)	(5,000)
Amortized Cost	34,483,000	34,483,000
Unrealized Gains	9,000	9,000
Unrealized Losses	(5,000)	(5,000)
Fair Value	34,487,000	34,487,000
Corporate debt securities
Available-for-sale securities
Aggregate Fair Value	40,587,000	40,587,000
Unrealized Losses	(20,000)	(20,000)
Amortized Cost	41,607,000	41,607,000
Unrealized Losses	(20,000)	(20,000)
Fair Value	$ 41,587,000	$ 41,587,000
Minimum
Available-for-sale securities
Expected average maturities period of marketable securities classified as available-for-sale		3 months
Maximum
Available-for-sale securities
Expected average maturities period of marketable securities classified as available-for-sale		12 months