Leases (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 168	$ 168
Operating lease payments	335	335
Operating lease right-of-use assets	1,258	1,258
Operating lease liabilities	$ 1,258	$ 1,258
Weighted average remaining lease term	1 year 10 months 24 days	1 year 10 months 24 days
Weighted average discount rate	3.10%	3.10%
2019	$ 319	$ 319
2020	578	578
2021	300	300
2022	61	$ 61
Lessor, Operating Lease, Existence of Option to Extend [true false]		true
Property, plant and equipment, gross	557,349	$ 557,349	$ 547,951	$ 538,927
Lease income	751	$ 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	$ 36,385	$ 36,385
Depreciation		$ 9,890
Commercial real estate leased to third parties | Maximum
Lessee, Lease, Description [Line Items]
Lessor, renewal term	60 years	60 years