Commitments and Contingencies Narrative (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($) ft²	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Line Items]
Total rental expense		$ 3,300	$ 2,600
Total future minimum operating lease payments	$ 1,200	10,804
Operating Leases, Future Minimum Payments Receivable, Current	$ 400
Operating Leases, Future Minimum Payments Receivable		100
Total future minimum lease payments of McCook facility		5,092
Property, plant and equipment, gross		85,226	84,939
Accumulated depreciation and amortization		61,678	57,606
Environmental Remediation Expense		500
Area of Real Estate Property | ft²	17,100
Operating Leases, Income Statement, Sublease Revenue	$ 700
Gain (Loss) on Contract Termination	500
Gain (Loss) on Termination of Lease	$ 200
Environmental Exit Costs, Reasonably Possible Additional Loss		1,400
Environmental Exit Costs, Assets Previously Disposed, Liability for Remediation		1,400
Headquarters
Commitments And Contingencies Disclosure [Line Items]
Total future minimum operating lease payments		4,000
McCook facility
Commitments And Contingencies Disclosure [Line Items]
Property, plant and equipment, gross		12,961	12,961
Accumulated depreciation and amortization			8,500
Capital leases
Commitments And Contingencies Disclosure [Line Items]
Property, plant and equipment, gross		$ 684	806
Accumulated depreciation and amortization			$ 300