Quarterly Results of Operations (Unaudited) (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Increase (decrease) to revenue		$ (21,800)	$ (4,500)	$ 1,600
Increase (decrease) to revenue, percent		(12.70%)	(3.30%)	1.30%
Increase (decrease) to gross profit		$ (7,500)	$ (2,200)	$ (1,200)
Increase (decrease) to gross profit, percent		(19.40%)	(7.20%)	(4.40%)
Gross profit as a percent of revenue		20.70%	21.80%	21.10%		22.40%	22.70%	22.30%	21.80%	22.70%	20.70%	22.40%
Increase (decrease) to selling, general, and administrative expense		$ (100)	$ (1,500)	$ 400
Increase (decrease) to selling, general, and administrative expense, percent		(0.50%)	(5.50%)	1.80%
Decline in environmental reserve			$ 3,700
Contingent loss related to patent litigation			3,200
Decline due to lower legal and professional services fees		$ 1,200
Increase (decrease) in interest expense, net		(100)		$ (200)
Decrease in other income				300
Foreign currency gain (loss)		(800)	100			$ 200	$ (700)
Income tax expense	$ 5,699	2,449	630	307	$ 3,420	2,280	811	$ 916	$ 937	$ 1,727	$ 3,385	$ 4,007	$ 9,084	$ 7,426	$ 18,967
Income (loss) before income taxes	$ 19,003	3,002	2,528	$ (355)	$ 14,910	11,310	2,456	$ 1,810	$ 2,173	$ 4,266	$ 5,174	$ 15,576	$ 24,177	$ 30,485	$ 37,076
Effective tax rate				6.90%					43.10%				37.60%	24.40%	51.20%
Increase (decrease) in effective tax rate								(33.10%)		40.50%
Selling, General and Administrative Expenses [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Non-cash charges to write-off unrealizable assets created as a result of unauthorized transactions		$ 2,700	$ 600	$ 1,800		$ 1,500	$ 1,000	$ 2,000