Stockholder's Equity (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Stockholders' Equity
Stock-based compensation expenses	$ 1,574,000	$ 1,388,000
Stock options plans
Stockholders' Equity
Stock-based compensation expenses	1,600,000
Total unrecognized compensation cost related to non-vested stock options granted (in dollars)	11,300,000
Period of recognition compensation cost	2 years 7 months 6 days
Fair value weighted-average assumptions:
Expected stock price volatility (as a percent)	82.00%	78.40%
Risk free interest rate (as a percent)	1.20%	1.10%
Expected life of options	6 years 3 months	6 years 3 months
Expected annual dividend per share (in dollars per share)	$ 0.00	$ 0.00
Number of Shares
Balance at the beginning of the period (in shares)	7,974,200
Options granted (in shares)	1,154,500
Options forfeited (in shares)	(47,600)
Balance at the end of the period (in shares)	9,081,100
Vested and unvested expected to vest at the end of the period (in shares)	8,012,500
Exercisable at the end of the period (in shares)	4,450,900
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 6.35
Options granted (in dollars per share)	$ 3.53
Options forfeited (in dollars per share)	$ 4.94
Balance at the end of the period (in dollars per share)	$ 5.99
Vested and unvested expected to vest at the end of the period (in dollars per share)	$ 6.10
Exercisable at the end of the period (in dollars per share)	$ 7.25
Weighted Average Remaining Contractual Life
Balance at the end of the period	7 years 6 months 4 days
Vested and unvested expected to vest at the end of the period	7 years 3 months 18 days
Exercisable at the end of the period	6 years
Aggregate Intrinsic Value
Aggregate intrinsic value of options outstanding (in dollars)	207,000
Aggregate intrinsic value of options vested and unvested expected to vest (in dollars)	132,000
Aggregate intrinsic value of options exercisable (in dollars)	$ 166,000