Employee Benefit Obligations - Net Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Change in Benefit Obligation
Projected benefit obligation at beginning of year	$ 8,241	$ 6,223
Interest cost	54	64
Company service cost	878	498
Employee contributions	417	321
Prior service cost	(314)
Benefits paid	341	422
Actuarial loss	700	713
Projected benefit obligation at end of year	10,317	8,241
Change in Plan Assets
Fair value of plan assets at beginning of year	5,978	4,433
Actual return on plan assets	882	320
Employer contributions	625	482
Employee contributions	417	321
Benefits paid	341	422
Fair value of plan assets at end of year	8,243	5,978
Funded Status at End of year
Excess of obligation over assets	(2,074)	(2,263)
Change in Accrued Benefit Liability
Accrued benefit liability at beginning of year	(2,263)	(1,790)
Company contributions made during year	625	482
Net periodic benefit cost for year	(1,036)	(529)
Net decrease (increase) in accumulated other comprehensive loss	600	(426)
Accrued benefit liability at end of year	(2,074)	(2,263)
Non - current plan assets	8,243	5,979
Non - current liability	10,317	8,242
Accrued benefit liability at end of year	(2,074)	(2,263)
Projected Benefit Payments
Projected year 1	166	148
Projected year 2	168	150
Projected year 3	172	152
Projected year 4	1,124	155
Projected year 5	163	1,069
Projected year 6-10	$ 1,053	$ 928