Leasing Arrangements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Capital Leases
2018	$ 938
2019	437
2020	21
2021	0
2022	0
Subsequent to 2022	0
Total minimum lease payments	1,396
Amounts representing interest	34
Present value of net minimum lease payments	1,362
Current maturities	912
Long-term capital lease obligation	450
Operating Leases
2018	3,359
2019	2,126
2020	1,929
2021	1,662
2022	1,059
Subsequent to 2022	2,329
Total minimum lease payments	12,464
Rental expense for all operating leases	4,900	$ 7,400	$ 9,800
Rental income on subleases of equipment	600	400	$ 300
Assets recorded under capital leases
Plant and equipment	4,807	4,807
Less accumulated depreciation	3,730	3,129
Assets recorded under capital leases	$ 1,077	$ 1,678