Annual report pursuant to Section 13 and 15(d)

Employee Benefit 401(k) Plans (Details)

v3.8.0.1
Employee Benefit 401(k) Plans (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]      
Minimum employee subscription rate, percentage of compensation 1.00%    
Maximum employee subscription rate, percentage of compensation 60.00%    
Employee pre-tax contributions vested percentage 100.00%    
Vesting rate 20.00%    
Percentage vested after total service period 100.00%    
Employees' vesting rights Participants are always 100 percent vested in their pre-tax contributions and will begin vesting in any matching or profit sharing contributions made on their behalf after two years of service with the Company at a rate of 20 percent per year, becoming 100 percent vested after a total of six years of service with the Company.    
Expenses for employee benefit plan $ 1,055,000 $ 1,029,000 $ 970,000
Minimum [Member]      
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]      
Employer contribution vesting period 2 years    
Maximum [Member]      
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]      
Employer contribution vesting period 6 years