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Share Capital - Textual (Details)
12 Months Ended
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
shares
Share Capital [Line Items]      
Proceeds from exercise of options | $   $ 0 $ 0
Stock-based compensation | $ $ 5,892,000 5,335,000 5,808,000
Tax benefit from compensation expense | $ $ 472,000 $ 1,401,000 2,030,000
Employee Stock Incentive Plan      
Share Capital [Line Items]      
Number of shares authorized | shares 15,650,000    
Employee Stock Option      
Share Capital [Line Items]      
Compensation cost not yet recognized | $ $ 225,000    
Compensation cost not yet recognized, period 3 years    
Weighted average price per share, options | $ / shares $ 2.23 $ 0.00  
Expected term 4 years 11 months    
Risk free interest rate 2.90%    
Expected volatility rate 52.90%    
Dividend yield 0.00%    
Award vesting period (years) 3 years    
Options, outstanding, weighted average remaining contractual term 3 years    
Number outstanding, expired and cancelled | shares 0    
Options, exercisable, intrinsic value | $   $ 125,000 471,000
Options outstanding, intrinsic value | $ $ 0    
Options vest | shares 111,866    
Number outstanding, granted | shares 0    
Restricted Stock And Restricted Stock Units      
Share Capital [Line Items]      
Equity instruments other than options, vested in period, fair value | $ $ 3,583,000 $ 7,316,000 $ 6,272,000
Stock Appreciation Rights (SARs)      
Share Capital [Line Items]      
Weighted average grant date fair value, granted | $ / shares $ 0.00    
Weighted average price per share | $ / shares $ 2.35 $ 2.35  
Equity instruments other than options, outstanding, weighted average remaining contractual terms 1 year 1 month    
Compensation cost not yet recognized, period 1 year 1 month    
Expected term 4 years    
Risk free interest rate 1.70%    
Expected volatility rate 46.20%    
Dividend yield 0.00%    
Number outstanding, expired and cancelled | shares 0    
Options vest | shares 0   0
Number outstanding, granted | shares 0    
Outstanding, intrinsic value | $ $ 0    
Nonvested awards, compensation not yet recognized, share-based awards other than options | $ $ 213,000    
Time Based Awards | Employee Stock Option      
Share Capital [Line Items]      
Weighted average grant date fair value, granted | $ / shares $ 7.38 8.98  
Weighted average price per share | $ / shares $ 9.83 11.94 $ 12.53
Compensation cost not yet recognized | $ $ 2,325,000    
Compensation cost not yet recognized, period 1 year 11 months 23 days    
Time Based Awards | Restricted Stock And Restricted Stock Units      
Share Capital [Line Items]      
Equity instruments other than options, outstanding, weighted average remaining contractual terms 1 year 11 months 23 days    
Performance Shares | Employee Stock Option      
Share Capital [Line Items]      
Weighted average grant date fair value, granted | $ / shares $ 9.17    
Weighted average price per share | $ / shares $ 9.15 $ 0.00 $ 14.00
Compensation cost not yet recognized | $ $ 260,000    
Common Class A      
Share Capital [Line Items]      
Number of votes per share 1    
Common Stock,value (in dollars per share) | $ / shares $ 0    
Common stock, shares issued | shares 57,517,568 56,371,376  
Common stock, shares outstanding | shares 57,517,568 56,371,376  
Common Class B      
Share Capital [Line Items]      
Number of votes per share 20    
Common Stock,value (in dollars per share) | $ / shares $ 0    
Common stock, shares issued | shares 3,755 3,755  
Common stock, shares outstanding | shares 3,755 3,755