Income Taxes (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Income Taxes      
Provision for income taxes $ 0 $ 0 $ 0
Deferred tax assets, before valuation allowance 34,208,000 22,804,000 14,400,000
Net operating loss carryforwards      
NOLs related to excess tax benefits 500,000    
Federal      
Net operating loss carryforwards      
Net operating loss carryforwards 95,100,000 62,300,000 40,500,000
State      
Net operating loss carryforwards      
Net operating loss carryforwards $ 16,600,000 $ 33,100,000 $ 11,300,000