Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Share Repurchase Agreement (Details)

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Summary of Significant Accounting Policies - Share Repurchase Agreement (Details) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Feb. 28, 2017
Apr. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Open market purchase of treasury shares $ 2,049,000      
Open market purchase of treasury shares, fees $ 16,000 $ 52,000    
Treasury Stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Open market purchase of common shares (in shares) 387,814 1,298,418    
Open market purchase of treasury shares $ 2,049,000 $ 6,387,000    
Common Class A        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock repurchase program, authorized amount (up to)     $ 15,000,000 $ 10,000,000