Stock Option and Purchase Plans (Details 3) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended			0 Months Ended		12 Months Ended
	Jan. 31, 2014 Stock options	Dec. 31, 2013 Stock options	Dec. 31, 2012 Stock options	Dec. 31, 2011 Stock options	Jun. 17, 2011 1994 Employee Stock Purchase Plan	Jun. 04, 2003 1994 Employee Stock Purchase Plan	Dec. 31, 2013 1994 Employee Stock Purchase Plan	Dec. 31, 2012 1994 Employee Stock Purchase Plan	Dec. 31, 2011 1994 Employee Stock Purchase Plan	Dec. 31, 2004 1994 Employee Stock Purchase Plan
Stock Option and Purchase Plans
Aggregate intrinsic value of outstanding options		$ 6.6
Aggregate intrinsic value of exercisable options		$ 6.6
Shares available for grant		1,976,823					498,095
Shares granted	1,128,100	4,166,292	2,850,118	1,289,790
Shares reserved for issuance to employees					2,000,000	1,400,000				800,000
Maximum percentage of base compensation that can be contributed by the eligible employee										10.00%
Percentage of purchase price of common stock at fair market value										85.00%
Additional term						10 years
Increase in the number of authorized shares					600,000	600,000
Plan term that was removed in an amendment to the plan					20 years
Cumulative number of shares issued under the plan							1,501,905
Weighted average fair value of share issued (in dollars per share)							$ 3.53	$ 3.72	$ 3.21