Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Details)

v3.7.0.1
Summary of Significant Accounting Policies - Additional Information (Details)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
USD ($)
Jun. 30, 2016
Jun. 30, 2017
USD ($)
Customer
Jun. 30, 2016
Dec. 31, 2016
USD ($)
Summary Of Significant Accounting Policies [Line Items]          
Allowances for doubtful accounts $ 65,000   $ 65,000   $ 63,000
Defined benefit obligation plan $ 787,000   $ 787,000   $ 837,000
Supplemental Executive Retirement Plan, tax status us-gaap:NonqualifiedPlanMember   us-gaap:NonqualifiedPlanMember   us-gaap:NonqualifiedPlanMember
Supplemental Executive Retirement Plan, funded status us-gaap:UnfundedPlanMember   us-gaap:UnfundedPlanMember   us-gaap:UnfundedPlanMember
Annual benefit payments, remainder of fiscal year $ 64,000   $ 64,000    
Annual benefit payments, year two 64,000   64,000    
Annual benefit payments, year three 64,000   64,000    
Annual benefit payments, year four 64,000   64,000    
Annual benefit payments, year five $ 64,000   $ 64,000    
Supplemental Executive Retirement Plan, Type us-gaap:SupplementalEmployeeRetirementPlanDefinedBenefitMember   us-gaap:SupplementalEmployeeRetirementPlanDefinedBenefitMember    
Income tax (benefit) expense $ (629,000)   $ (629,000)    
Deferred income tax (benefit) (926,000)   (926,000)    
Uncertain tax positions $ 0   $ 0    
Net Sales | Customer Concentration Risk          
Summary Of Significant Accounting Policies [Line Items]          
Concentration risk, percentage 100.00% 100.00% 100.00% 100.00%  
Net Sales | Customer Concentration Risk | Caterpillar Inc and CEG Distributions PTY Ltd          
Summary Of Significant Accounting Policies [Line Items]          
Concentration risk, percentage 32.00% 28.00% 30.00% 32.00%  
Accounts Receivable | Customer Concentration Risk          
Summary Of Significant Accounting Policies [Line Items]          
Maximum insurance policy limit of liability $ 8,600,000   $ 8,600,000    
Accounts Receivable | Customer Concentration Risk | Caterpillar Inc and CEG Distributions PTY Ltd          
Summary Of Significant Accounting Policies [Line Items]          
Concentration risk, percentage     62.00%   64.00%
Number of major customers | Customer     2    
Federal and State          
Summary Of Significant Accounting Policies [Line Items]          
Income tax (benefit) expense 297,000        
Accrued Other          
Summary Of Significant Accounting Policies [Line Items]          
Defined benefit obligation plan 64,000   $ 64,000   $ 64,000
Other Long-Term Liabilities          
Summary Of Significant Accounting Policies [Line Items]          
Defined benefit obligation plan $ 723,000   $ 723,000   $ 773,000