Pension Plans - Defined benefit plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in benefit obligation:
Benefit obligation at beginning of year	$ 14,268,000	$ 13,265,000
Interest cost	463,000	468,000	$ 462,000
Actuarial (gain) loss	(976,000)	914,000
Benefits paid	(396,000)	(379,000)
Benefit obligation at end of year	13,359,000	14,268,000	13,265,000
Change in plan assets:
Fair value of plan assets at beginning of year	10,299,000	8,166,000
Actual (loss) gain on plan assets	(216,000)	1,293,000
Employer contribution	1,750,000	1,216,000
Benefits paid	(396,000)	(379,000)
Other	3,000	3,000
Fair value of plan assets at end of year	11,440,000	10,299,000	8,166,000
Unfunded status	(1,919,000)	(3,969,000)
Amounts recognized in consolidated balance sheets
Accrued liabilities	(1,146,000)	(1,150,000)
Liability for pension benefits	(773,000)	(2,819,000)
Total	(1,919,000)	(3,969,000)
Amounts recognized in accumulated other comprehensive loss that have not been recognized as components of net periodic benefit (expense)
Net actuarial loss, pre-tax	5,708,000	5,923,000
Components of net periodic pension benefit
Interest cost	463,000	468,000	462,000
Expected return on plan assets	(699,000)	(644,000)	(622,000)
Recognized net actuarial loss	151,000	143,000	126,000
Total net periodic pension benefit	(85,000)	$ (33,000)	$ (34,000)
Amounts expected to recognized as components of net periodic benefit (expense), which are included in accumulated other comprehensive loss
Actuarial loss	$ 145,000
Net Periodic Pension Cost
Weighted-average discount rate (as a percent)	3.80%	4.20%	4.40%
Expected long-term rate of return on plan assets (as a percent)	6.50%	8.00%	8.00%
Benefit Obligation
Weighted-average discount rate (as a percent)	4.40%	3.80%