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Employee Benefit Plans (Details) - USD ($)
3 Months Ended 9 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Mar. 31, 2017
Retirement Benefits [Abstract]          
Employer Matching Contribution, Percent of Match     6.00%    
Employees’ Capital Accumulation Plan, Total expense recognized $ 30,800,000 $ 28,100,000 $ 92,700,000 $ 84,800,000  
Employees’ Capital Accumulation Plan, Company-paid contributions 15,400,000 13,700,000 46,500,000 44,500,000  
Supplemental Employee Retirement Plan          
Defined Benefit Plan Disclosure [Line Items]          
Deferred Compensation Arrangement with Individual, Annual Cash Award Granted per Year of Service, Amount     10,000    
Officer Medical Plan          
Defined Benefit Plan Disclosure [Line Items]          
Service cost 1,116,000 1,213,000 3,348,000 3,638,000  
Interest cost 1,252,000 1,196,000 3,756,000 3,587,000  
Net actuarial loss 568,000 762,000 1,703,000 2,287,000  
Total benefit cost 2,936,000 $ 3,171,000 8,807,000 $ 9,512,000  
Defined benefit plan, unfunded status of plan $ 122,600,000   $ 122,600,000   $ 118,100,000