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Employee Benefit Plans - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]            
Expected pension and postretirement benefit costs     $ 1,600      
Expected amortization of pre merger regulatory asset     769      
Florida Public Utilities Company Pension Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Unamortized balance of regulatory asset $ 1,700   1,700     $ 2,100
Defined Benefit Plan, Net Periodic Benefit Cost 55 $ 57 110 $ 114    
Contribution to pension plan 1,154   1,529      
Chesapeake Pension Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plan, Net Periodic Benefit Cost 82 77 165 155    
Contribution to pension plan 119   167      
Chesapeake Pension SERP [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plan, Net Periodic Benefit Cost 44 45 88 90    
Contribution to pension plan 38   76      
Chesapeake Postretirement Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plan, Net Periodic Benefit Cost 8 8 14 15    
Contribution to pension plan 17,102   64,632      
Florida Public Utilities Company Medical Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plan, Net Periodic Benefit Cost 13 $ 14 26 $ 28    
Contribution to pension plan $ 18,477   $ 35,511      
Scenario, Forecast [Member] | Florida Public Utilities Company Pension Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year         $ 3,000  
Scenario, Forecast [Member] | Chesapeake Pension Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year         746  
Scenario, Forecast [Member] | Chesapeake Pension SERP [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year         151  
Scenario, Forecast [Member] | Chesapeake Postretirement Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year         83  
Scenario, Forecast [Member] | Florida Public Utilities Company Medical Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year         $ 129