Leases (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Lessee, Lease, Description [Line Items]
Remaining lease term	3 years
Operating lease cost	$ 167
Operating lease payments	167
Operating lease right-of-use assets	1,370
Operating lease liabilities	$ 1,370
Weighted average remaining lease term	2 years 1 month 6 days
Weighted average discount rate	3.10%
2019	$ 511
2020	534
2021	274
2022	$ 51
Lessor, Operating Lease, Existence of Option to Extend [true false]	true
Property, plant and equipment, gross	$ 553,609	$ 547,951	$ 534,336
Commercial real estate leased to third parties
Lessee, Lease, Description [Line Items]
Property, plant and equipment, gross	36,371
Depreciation	9,709
Proceeds from lease payments	$ 749
Commercial real estate leased to third parties | Maximum
Lessee, Lease, Description [Line Items]
Lessor, renewal term	60 years