Annual report pursuant to Section 13 and 15(d)

Benefit Plans and Collective Bargaining Agreements - Non-Union Employees Narrative (Details)

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Benefit Plans and Collective Bargaining Agreements - Non-Union Employees Narrative (Details) - 401(k) Employee Stock Ownership Plan - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]      
Employee maximum contribution percentage 100.00%    
Employee maximum contribution amount $ 19,000    
Minimum age to qualify under Economic Growth and Tax Relief Reconciliation Act 50 years    
Employee additional contribution eligible under economic growth and tax relief reconciliation act $ 6,000    
Employee maximum contribution eligible under economic growth and tax relief reconciliation act $ 25,000    
Employer maximum contribution percentage match 100.00%    
Matching percentage by employer of employees' gross pay 4.00%    
Matching contributions made by employer $ 800,000 $ 700,000 $ 600,000
Employer discretionary contribution $ 0 $ 0 $ 0