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Employee Benefit and Deferred Compensation Plans - Additional Information (Details)
 12 Months Ended
Dec. 31, 2020
USD ($)
plan
point
shares
Dec. 31, 2019
USD ($)
shares
Dec. 31, 2018
USD ($)
shares
Dec. 31, 2007
officer
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Accumulated benefit obligation $ 28,226,000 $ 28,020,000    
Retiring age limit, minimum 55 years      
Retiring age limit, maximum 65 years      
Eligible employee from service (in years) 15 years      
Number of points for eligibility (points) | point 70      
Minimum eligible age for Medicare coverage 65 years      
Expected company contributions $ 360,000      
Health care cost trend rate (percent) 5.40%      
Redemption notice 60 days      
Employee deferrals (percent) 4.00%      
Percentage of plan compensation as nondiscretionary contribution 5.00%      
Percentage of plan compensation in excess of social security wage base 5.00%      
Hours of service credited to the employees during the year 1000 hours      
Employee deferrals amounts $ 17,888,000 16,009,000 $ 13,477,000  
Number of conventional deferred compensation plans | plan 2      
Company's deferred compensation plan expense $ 3,965,000 3,610,000 1,290,000  
Number of officers provided for | officer       4
Expiration period subsequent to retirement       15 years
Supplemental executive retirement liabilities totaled 3,816,000 3,921,000    
Incentive compensation plan expense $ 6,425,000 $ 4,200,000 $ 5,117,000  
Option expiration period 10 years      
Granted (shares) | shares 0 0 0  
Intrinsic value of options exercised $ 279,000 $ 290,000 $ 1,180,000  
Common shares reserved for issuance under employee benefit plans (shares) | shares 2,871,774      
401(k) Plan        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Common shares reserved for issuance under employee benefit plans (shares) | shares 957,320      
Deferred Stock Unit Plan        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Common shares reserved for issuance under employee benefit plans (shares) | shares 22,577      
2011 Long-Term Incentive Compensation Plan        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Common shares reserved for issuance under employee benefit plans (shares) | shares 1,758,149      
Stock compensation plan        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Compensation expense $ 0 0 0  
Performance- Based Restricted Stock        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Compensation expense 10,419,000 10,046,000 7,251,000  
Time- Based Restricted Stock        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Unrecognized stock-based compensation expense $ 10,185,000      
Weighted average period over which unrecognized expense is expected to be recognized (in years) 1 year 10 months 6 days      
Growth Investment        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Equity income strategy (percent) 55.00%      
Real Estate | Growth Investment        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Equity income strategy (percent) 5.00%      
Interest Rate Contract | Growth Investment        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Equity income strategy (percent) 45.00%      
Pension Benefits        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Company contribution to pension benefit plan $ 0 0    
Accumulated benefit obligation 28,226,000 28,020,000 $ 24,945,000  
Other Postretirement Benefits Plan        
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]        
Company contribution to pension benefit plan $ 214,000 $ 151,000