Leases (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 258	$ 168	$ 258	$ 168
Operating lease payments	494	335	494	335
Operating lease right-of-use assets	1,265	1,258	1,265	1,258	$ 1,580
Operating lease liabilities	$ 1,265	$ 1,258	$ 1,265	$ 1,258
Weighted average remaining lease term	1 year 3 months 18 days	1 year 10 months 24 days	1 year 3 months 18 days	1 year 10 months 24 days
Weighted average discount rate	3.00%	3.10%	3.00%	3.10%
2020	$ 506		$ 506
2021	666		666
2022	88		88
2023	5		$ 5
Lessor, Operating Lease, Existence of Option to Extend [true false]			true
Property, plant and equipment, gross	570,895	$ 557,349	$ 570,895	$ 557,349	$ 567,215
Lease income	788	751	$ 1,526	1,500
Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term			3 years
Commercial real estate leased to third parties
Lessee, Lease, Description [Line Items]
Property, plant and equipment, gross	$ 36,378	$ 36,385	$ 36,378	36,385
Depreciation			$ 10,613	$ 9,890
Commercial real estate leased to third parties | Maximum
Lessee, Lease, Description [Line Items]
Lessor, renewal term	60 years		60 years