Retirement Plans - Other (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) employee item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Projected benefit obligation:
Balance, beginning of the year	$ 2,865	$ 2,682
Service cost	109	112	$ 82
Interest cost	104	102	105
Actuarial (gain) loss	(45)	53
Benefits paid to participants	(6)	(84)
Balance, end of year	3,027	2,865	2,682
Funded status of the plan
Excess of benefit obligation over the value of plan assets	(3,027)	(2,865)	(2,682)
Unrecognized net actuarial loss	818	905	904
Unrecognized prior service cost	52	69	86
Accrued benefit cost	(2,157)	(1,891)	(1,692)
Net amounts recognized in the consolidated balance sheets
Accrued benefit cost	(3,027)	(2,865)
Accumulated other comprehensive loss	870	974
Accrued benefit cost	(2,157)	$ (1,891)	(1,692)
Benefits expected to be paid in each of the next five years and thereafter
2017	186
2018	246
2019	121
2020	123
2021	205
2022 through 2025	870
Total	$ 1,751
Weighted-average rates used
Discount rate on the benefit obligation (as a percent)	3.78%	3.90%
Rate of employee compensation increase (as a percent)	4.00%	4.00%
Pension expense
Service cost	$ 109	$ 112	82
Interest cost	104	102	105
Amortization of prior service cost	17	17	17
Net loss amortization	42	51	27
Net periodic benefit cost	$ 272	$ 282	$ 231
WAPA
Number of months to be in service for applicability of retirement plan	3 months
Number of weeks per year of service for one-time lump sum payment at retirement	14 days
Maximum number of retirees per year under the plan | employee	5
Number of retirees per year under the retirement plan | item	164
WAPA | Maximum
Number of weeks per year of service for one-time lump sum payment at retirement	315 days