Stockholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended				105 Months Ended		105 Months Ended		84 Months Ended		12 Months Ended		84 Months Ended		1 Months Ended	12 Months Ended			84 Months Ended
	Dec. 31, 2005 item	Dec. 31, 2004 item	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2004 1996 Equity Incentive Plan	Mar. 31, 1996 1996 Equity Incentive Plan	Dec. 31, 2004 1996 Equity Incentive Plan Stock Options	Dec. 31, 2004 1996 Equity Incentive Plan Stock Options Minimum	Dec. 31, 2012 1996 Non-Employee Directors' Stock Option Plan	Mar. 31, 1996 1996 Non-Employee Directors' Stock Option Plan	Dec. 31, 2012 1996 Non-Employee Directors' Stock Option Plan Stock Options	Dec. 31, 2012 1996 Non-Employee Directors' Stock Option Plan Stock Options Minimum	Dec. 31, 2012 2005 Equity Incentive Plan	Dec. 31, 2005 2005 Equity Incentive Plan	May 31, 2007 ESPP	Dec. 31, 2012 ESPP	Dec. 31, 2011 ESPP	Dec. 31, 2010 ESPP	Dec. 31, 2012 ESPP	Mar. 31, 1996 ESPP
Stock Options and Employee Stock Purchase Plan
Number of Plans	1	2
Common stock, reserved for future issuance (in shares)						1,725,000				175,000			19,260,045	7,560,045						400,000
Authorized shares in excess of transferred from predecessor plans														3,990,000
Additional shares reserved for future issuance					4,100,000				250,000				11,700,000		500,000
Price as a percentage of fair market value of common stock								100.00%				100.00%				85.00%
Stock option granted term							10 years				10 years
Vesting period							4 years				4 years
Number of shares available for issuance													3,161,755		900,000	154,856			154,856
Stock issued during period, shares, employee stock purchase plans																120,320	80,160	78,991	745,144
Receivables from stock option exercise			$ 534	$ 434