Income Taxes (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes
Federal and state net operating loss carryforwards relate to deductions for stock option compensation	$ 10,300,000
Change in the valuation allowance against the deferred tax assets
Balance at beginning of period	132,683,000	103,881,000	81,420,000
Additions	36,968,000	28,802,000	22,461,000
Balance at end of period	169,651,000	132,683,000	103,881,000
Research and development | Federal
Tax credit carryforward
Amount of tax credit carryforward	11,100,000
Research and development | State
Tax credit carryforward
Amount of tax credit carryforward	4,800,000
Investment | State
Tax credit carryforward
Amount of tax credit carryforward	$ 400,000