Employee Benefit Plans - Narrative (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) agreement	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan with individual requisite age	21 years
Defined benefit plan with individual requisite service period	1 year
Accumulated benefit obligation	$ 8,313,000	$ 7,932,000	$ 8,453,000
Maximum percentage of limiting equities	5.00%
Employer matching contribution, service requirement	1 year
Employee benefits expense	$ 763,000	623,000	602,000
Period of deferred compensation agreements	10 years
Number of remaining agreements | agreement	1
Deferred compensation liability	$ 350,000	397,000
Deferred compensation arrangement expense	3,000	6,000	8,000
Profit sharing and incentive arrangements expense	1,243,000	$ 916,000	$ 559,000
Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred compensation arrangement annual payments	25,000
Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Deferred compensation arrangement annual payments	$ 50,000