Leases (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 257	$ 411	$ 257	$ 411
Operating lease payments	751	746	751	746
Operating lease right-of-use assets	1,062	1,770	1,062	1,770	$ 1,580
Operating lease liabilities	$ 1,062	$ 1,770	$ 1,062	$ 1,770
Weighted average remaining lease term	1 year	1 year 10 months 24 days	1 year	1 year 10 months 24 days
Weighted average discount rate	3.00%	3.10%	3.00%	3.10%
2020	$ 249		$ 249
2021	721		721
2022	88		88
2023	4		$ 4
Lessor, Operating Lease, Existence of Option to Extend [true false]			true
Property, plant and equipment, gross	576,250	$ 561,666	$ 576,250	$ 561,666	$ 567,215
Lease income	$ 802	733	$ 2,328	2,232
Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term	3 years		3 years
Commercial real estate leased to third parties
Lessee, Lease, Description [Line Items]
Property, plant and equipment, gross	$ 36,378	$ 36,362	$ 36,378	36,362
Depreciation			$ 10,794	$ 10,071
Commercial real estate leased to third parties | Maximum
Lessee, Lease, Description [Line Items]
Lessor, renewal term	60 years		60 years