Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Differences between the actual tax provision (benefit) and the tax provision (benefit) computed using the United States federal income tax rate
Provision (benefit) at statutory rate	$ (21,349,000)	$ (16,109,000)	$ (12,739,000)
State taxes, net of federal benefit	(3,220,000)	(2,379,000)	(1,967,000)
State tax rate change		84,000	196,000
State net operating loss expiration	3,167,000	2,867,000	3,820,000
Stock-based compensation	382,000	373,000	791,000
Tax credits	(411,000)	(1,537,000)	(1,686,000)
Other	22,000	259,000	(78,000)
(Decrease) increase in valuation allowance	21,409,000	16,442,000	11,663,000
Deferred tax assets:
Federal and state net operating loss carryforwards	143,988,000	123,463,000
Federal and state research and experimentation credits	17,225,000	16,796,000
Depreciation and amortization	2,594,000	2,776,000
Deferred compensation	5,368,000	5,077,000
Other	1,014,000	667,000
Deferred tax assets	170,189,000	148,779,000
Less valuation allowance	(170,189,000)	(148,779,000)
Increase (decrease) in valuation allowance	$ 21,400,000	$ 16,400,000	$ 11,700,000