Commitments and Contingencies Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments And Contingencies Disclosure [Line Items]
Total rental expense	$ 2,600	$ 2,200	$ 2,000
Total future minimum operating lease payments	13,872
Operating Leases, Future Minimum Payments Receivable	500
Total future minimum lease payments of McCook facility	6,222
Property, plant and equipment, gross	84,939	85,856
Accumulated depreciation and amortization	57,606	54,949
Environmental Remediation Expense	0	0	$ 931
Accrual for Environmental Loss Contingencies	1,000
Headquarters
Commitments And Contingencies Disclosure [Line Items]
Total future minimum operating lease payments	6,400
McCook facility
Commitments And Contingencies Disclosure [Line Items]
Property, plant and equipment, gross	12,961	12,961
Accumulated depreciation and amortization	7,200
Capital leases
Commitments And Contingencies Disclosure [Line Items]
Property, plant and equipment, gross	806	$ 534
Accumulated depreciation and amortization	400
Minimum
Commitments And Contingencies Disclosure [Line Items]
Environmental Exit Costs, Anticipated Cost	300
Maximum
Commitments And Contingencies Disclosure [Line Items]
Environmental Exit Costs, Anticipated Cost	$ 1,400