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Employee Benefit Plan (Details)
 12 Months Ended
Dec. 31, 2017
USD ($)
Officers
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Profit Sharing and 401(k) Plan for eligible employees [Member]      
Employee Benefit Plan (Textual)      
Defined benefit plan, annual cost $ 476,000 $ 356,000 $ 326,000
Supplemental Executive Retirement Plan (nonqualified deferred compensation plan) [Member]      
Employee Benefit Plan (Textual)      
Defined benefit plan, annual cost $ 792,000 782,000 $ 978,000
Number of executive officers | Officers 20    
Accrued benefit obligation $ 5,400,000 $ 4,600,000