Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Differences between the actual tax provision (benefit) and the tax provision (benefit) computed using the United States federal income tax rate
Benefit at statutory rate	$ (29,293,000)	$ (30,665,000)	$ (21,349,000)
State taxes, net of federal benefit	(3,342,000)	(3,735,000)	(3,220,000)
State net operating loss expiration		661,000	3,167,000
Stock-based compensation	1,094,000	1,118,000	382,000
Tax credits	(1,720,000)	(2,462,000)	(411,000)
Foreign rate differential	6,243,000	5,252,000
Other	100,000	(47,000)	22,000
Increase in valuation allowance	26,918,000	29,878,000	21,409,000
Deferred tax assets:
Federal and state net operating loss carryforwards	194,091,000	170,557,000
Federal and state research and development credits	21,401,000	19,675,000
Depreciation and amortization	2,423,000	2,412,000
Deferred compensation	7,643,000	6,254,000
Other	1,427,000	1,169,000
Deferred tax assets	226,985,000	200,067,000
Less valuation allowance	(226,985,000)	(200,067,000)
Increase (decrease) in valuation allowance	$ 26,900,000	$ 29,900,000	$ 21,400,000