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Employee Benefit Plans Employee Benefit Plans 1 (Details) - Pension Benefits
$ in Thousands
 12 Months Ended
Dec. 31, 2019
USD ($)
item
participant
Dec. 31, 2018
USD ($)
Employee benefit plans    
Defined Benefit Plan Amounts Recognized in Regulatory Asset, Liability New Prior Service Cost (Credit) | $ $ 0 $ 3,626
Minimum age for eligibility under the Pension Plan | item 21  
Minimum period of service for eligibility under the Pension Plan 5 years  
Normal retirement benefit (as a percent) 2.00%  
Defined Benefit Plan Number of Highest Consecutive Years Average Earnings Used in Computing Retirement Benefit 5 years  
Maximum number of years of credited service considered in determining retirement benefit 40 years  
Number of participants in the Pension Plan | participant 939  
Eligibility for employer matching contributions, period of service 3 years  
Maximum [Member]    
Employee benefit plans    
Percentage of participant's eligible pay contributed to the plan by the employer 5.25%  
Minimum    
Employee benefit plans    
Percentage of participant's eligible pay contributed to the plan by the employer 3.00%