Stock option and incentive plan (Details Textual) (USD $)
 12 Months Ended 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2009
Officer [Member]
Dec. 31, 2012
Former Outside Directors [Member]
Dec. 31, 2009
Former Outside Directors [Member]
Dec. 31, 2009
Former Outside Directors [Member]
Maximum [Member]
Dec. 31, 2009
Former Outside Directors [Member]
Minimum [Member]
Dec. 31, 2010
Outside Consultants [Member]
Dec. 31, 2011
Executive Officer [Member]
Dec. 31, 2012
Chief Executive Officer [Member]
Dec. 31, 2011
Chief Executive Officer [Member]
Dec. 31, 2012
Common Stock [Member]
Dec. 31, 2009
Plan 2007 [Member]
Dec. 31, 2012
Plan 2007 [Member]
Dec. 31, 2012
Plan 2010 [Member]
Dec. 31, 2011
Plan 2010 [Member]
Dec. 31, 2010
Plan 2010 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross 1,375,000   4,600,000   100,000     800,000 750,000 1,400,000 3,000,000            
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period                   3 years 7 years            
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value $ 15,000,000 $ 5,200,000                              
Allocated Share-based Compensation Expense 1,400,000 900,000                              
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized                             2,500,000    
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized 3,100,000                                
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition 1 year 7 months 6 days                                
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value 5,700,000 114,000   14,000                          
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized                           10,000,000 5,000,000    
Defined Contribution Plan, Employer Discretionary Contribution Amount 219,000                                
Employee Stock Purchase Plan, Value Of Shares, Maximum 500,000                                
Stock Issued During Period, Shares, Employee Stock Purchase Plans                       9,964          
Weighted average grant-date fair valueof granted options $ 1.51 $ 0.72                              
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value 30,600,000                                
Share Based Compensation Award Number Of Shares Issued In Excess Of Cap                         1,600,000     2,500,000 250,000
Share-Based Compensation Arrangements By Share-Based Payment Award, Options, Grants In Period, Weighted Average Exercise Price $ 2.77         $ 0.16 $ 0.14 $ 0.45 $ 0.46                
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense $ 351,000 $ 0