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Employee Benefit Plans (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2018
USD ($)
officers
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
401(k) Savings Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Minimum age requirement 21 years    
Minimum service period required 3 months    
Employer matching contribution, percent of match 75.00%    
Maximum annual contribution per employee, percent 8.00%    
Total cost recognized for the period $ 5,200 $ 4,400 $ 2,600
Postretirement Life Insurance      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Base amount of death proceeds, annual percentage increase until retirement age is reached 3.00%    
Period death benefit required to be paid within following participant's death 90 days    
Total cost recognized for the period $ 6,900 7,800 6,600
Deferred compensation plan | Directors and officers      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Deferred compensation liability 1,000 1,100  
Deferred compensation plan, period expense 22 21 23
Long term incentive plan | Named executive officers ('NEO')      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Deferred compensation plan, period expense $ 510 $ 455 $ 418
Number of officers currently participating in the LTIP | officers 2    
Long term incentive plan | Named executive officers ('NEO') | Minimum      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Deferred compensation plan, requisite service period 5 years    
Long term incentive plan | Named executive officers ('NEO') | Maximum      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Deferred compensation plan, requisite service period 10 years    
Vested after 2 Years of Service | 401(k) Savings Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Contribution Plan, Employer Matching Contribution, Vesting Percentage 25.00%    
Vested after 3 Years of Service | 401(k) Savings Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Contribution Plan, Employer Matching Contribution, Vesting Percentage 50.00%    
Vested after 4 Years of Service | 401(k) Savings Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Contribution Plan, Employer Matching Contribution, Vesting Percentage 75.00%    
Vested after 5 or More Years of Service | 401(k) Savings Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Defined Contribution Plan, Employer Matching Contribution, Vesting Percentage 100.00%