Annual report pursuant to Section 13 and 15(d)

Business and summary of significant accounting policies - Concentrations of credit risk (Details)

v3.7.0.1
Business and summary of significant accounting policies - Concentrations of credit risk (Details) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Concentration Risk [Line Items]    
Cash balances in excess of federally insured limits $ 789,157 $ 897,383
Allowance for uncollectible accounts receivable $ 0 $ 0
Total Revenue | Geographic Concentration Risk | New York Downtown    
Concentration Risk [Line Items]    
Concentration risk, percentage 9.00% 10.00%
Total Revenue | Geographic Concentration Risk | New York Midtown    
Concentration Risk [Line Items]    
Concentration risk, percentage 9.00% 9.00%
Total Revenue | Geographic Concentration Risk | Las Vegas    
Concentration Risk [Line Items]    
Concentration risk, percentage 17.00% 17.00%
Total Revenue | Geographic Concentration Risk | London    
Concentration Risk [Line Items]    
Concentration risk, percentage 11.00% 15.00%