Employee Benefit Plans (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) h	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Mandatory work hours per year | h	1,000
Mandatory 401(k) match	$ 0.25
Maximum annual employer 401(k) contribution	6.00%
Amount expensed for 401(k) contributions	$ 904,000	$ 841,000	$ 759,000
Accrued liability for plan	1,500,000	1,600,000
Increase (decrease) in non-qualified deferred compensation plan	(140,000)	199,000	99,000
Aggregate payout under profit sharing plan	1,200,000	1,100,000	1,200,000
Supplemental Employee Retirement Plan
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Contributions to supplemental plan	264,000	299,000	228,000
Accrued liability for plan	2,300,000	2,600,000
RML
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Amount expensed for 401(k) contributions	$ 164,000	190,000	172,000
Term of service required	3 months
Age requirement	20 years 6 months
RML | Supplemental Employee Retirement Plan
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Contributions to supplemental plan	$ 600,000	673,000	$ 692,000
Accrued liability for plan	$ 3,300,000	$ 2,900,000
Vesting period	10 years