Basis of Statement Presentation (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended				9 Months Ended		12 Months Ended
	Oct. 20, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Common stock, par value (in dollars per share)		$ 0.001				$ 0.001		$ 0.001
Accounts payable						$ (18,060)	$ (1,167)
Net cash provided by (used for) operations						24,663	35,364
Capital expenditures						(25,576)	(47,800)
Net cash (used for) investing activities						(25,576)	(47,800)
Accrued additions to plant assets						5,242	5,073
Cost of goods sold		$ (156,685)			$ (161,706)	(460,333)	(495,259)
Foreign exchange loss (gain)		373			(531)	(478)	409
Income before income taxes		9,324			$ 11,580	33,126	35,406
Inventories		$ 170,290				$ 170,290		$ 180,203
Inventory And AOCI Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of goods sold			$ 3,100
Foreign exchange loss (gain)			700
Income before income taxes			3,800
Inventories			3,100
Other comprehensive income before tax			$ 700
Prior period reclassification adjustment				$ 1,200				$ 2,600
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accounts payable							(5,664)
Net cash provided by (used for) operations							30,867
Capital expenditures							(43,303)
Net cash (used for) investing activities							(43,303)
Restatement Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accounts payable							4,497
Net cash provided by (used for) operations							4,497
Capital expenditures							(4,497)
Net cash (used for) investing activities							(4,497)
Accrued additions to plant assets							$ 5,073
Subsequent Event
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Common stock, par value (in dollars per share)	$ 0.001
Stock valuation at date of merger (in dollars per share)	$ 32.00
Iris Merger Sub 2019, Inc | Subsequent Event
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Merger, net purchase price	$ 932,000
Merger, contingent asset	40,000
Iris Merger Sub 2019, Inc | Minimum | Subsequent Event
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Merger, contingent liability	10,300
Iris Merger Sub 2019, Inc | Maximum | Subsequent Event
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Merger, contingent liability	$ 20,600