Quarterly Result of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended			72 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 112,844	$ 99,705	$ 98,244	$ 92,834	$ 106,423	$ 90,250	$ 82,682	$ 81,562	$ 403,627	$ 360,917	$ 325,584
Segment profit	64,551	52,317	57,691	53,786	62,094	52,034	46,760	43,749	228,345	204,637	177,960
Net income	5,758	$ (2,488)	$ 1,205	$ 455	$ (11,058)	$ 1,628	$ (3,625)	$ (1,461)	4,930	(14,516)	11,107
INCOME TAX (BENEFIT) EXPENSE	$ 1,000								$ (372)	$ 20,343	$ 1,519
Net income (loss) per share:
Basic (loss) EPS (in dollars per share)	$ 0.33	$ (0.15)	$ 0.07	$ 0.03	$ (0.66)	$ 0.10	$ (0.22)	$ (0.09)	$ 0.29	$ (0.87)	$ 0.67
Diluted EPS (in dollars per share)	$ 0.33	$ (0.15)	$ 0.07	$ 0.03	$ (0.66)	$ 0.10	$ (0.22)	$ (0.09)	$ 0.29	$ (0.87)	$ 0.67
Disaggregation of Revenue [Line Items]
Provision for excess and obsolete inventory		$ 4,700							$ 5,757	$ 1,734	$ 4,134
Tax Cuts And Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)					$ (19,400)
Tax cuts and jobs act of 2017, incomplete accounting, transition tax for accumulated foreign earnings, provisional income tax expense					17,400				17,400
Tax Cuts And Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Provisional Income Tax Expense (Benefit)					$ (2,000)				$ (2,000)
Government Contract
Quarterly Financial Information Disclosure [Abstract]
Sales												$ 53,500
Disaggregation of Revenue [Line Items]
Charges to income from price adjustment clauses	$ 4,800											$ 4,800