Adoption of Accounting Standards Codification 606 - Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 29, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 3,573		$ 2,150	$ 3,689	$ 7,432
Accounts receivable, net of allowance for doubtful accounts of $1,212 and $868 at September 29, 2018 and December 31, 2017, respectively	64,466		74,064
Contract assets	88,066	$ 68,739	0
Inventories	101,752	83,159	122,161
Production cost of contracts	12,021		11,204
Other current assets	12,124		11,435
Total Current Assets	282,002		221,014
Property and equipment, net of accumulated depreciation of $159,010 and $143,216 at September 29, 2018 and December 31, 2017, respectively	106,583		110,252
Goodwill	135,769		117,435
Intangibles, net	114,746		114,693
Non-current deferred income taxes	131	166
Other assets	3,334		3,098
Total Assets	642,565		566,753
Current Liabilities
Accounts payable	73,534		51,907
Contract liabilities	15,108	24,460	0
Accrued liabilities	31,929	22,238	28,329
Total Current Liabilities	120,571		80,236
Long-term debt	229,402		216,055
Non-current deferred income taxes	19,427	18,589
Other long-term liabilities	17,608		18,898
Total Liabilities	387,008		331,170
Commitments and contingencies (Notes 11, 13)
Equity [Abstract]
Common stock - $0.01 par value; 35,000,000 shares authorized; 11,409,623 and 11,332,841 shares issued and outstanding at September 29, 2018 and December 31, 2017, respectively	114		113
Additional paid-in capital	82,447		80,223
Retained earnings	179,412	170,029	161,364
Accumulated other comprehensive loss	(6,416)		(6,117)
Total Shareholders’ Equity	255,557		235,583
Total Liabilities and Shareholders’ Equity	642,565		566,753
Accounts receivable, allowance for doubtful accounts	1,212		868
Property and equipment, accumulated depreciation	$ 159,010		$ 143,216
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01
Common stock, shares authorized (in shares)	35,000,000		35,000,000
Common stock, shares issued (in shares)	11,409,623		11,332,841
Common Stock, shares outstanding (in shares)	11,409,623		11,332,841
Calculated under Revenue Guidance in Effect before Topic 606
Current Assets
Cash and cash equivalents	$ 3,573		$ 2,150
Accounts receivable, net of allowance for doubtful accounts of $1,212 and $868 at September 29, 2018 and December 31, 2017, respectively	64,466
Contract assets	0		0
Inventories	161,431		122,161
Production cost of contracts	12,021
Other current assets	11,600
Total Current Assets	253,091
Property and equipment, net of accumulated depreciation of $159,010 and $143,216 at September 29, 2018 and December 31, 2017, respectively	106,583
Goodwill	135,769
Intangibles, net	114,746
Non-current deferred income taxes	261		261
Other assets	3,334
Total Assets	613,784
Current Liabilities
Accounts payable	73,534
Contract liabilities	0		0
Accrued liabilities	36,034		28,329
Total Current Liabilities	109,568
Long-term debt	229,402
Non-current deferred income taxes	15,676		15,981
Other long-term liabilities	17,608
Total Liabilities	372,254
Commitments and contingencies (Notes 11, 13)
Equity [Abstract]
Common stock - $0.01 par value; 35,000,000 shares authorized; 11,409,623 and 11,332,841 shares issued and outstanding at September 29, 2018 and December 31, 2017, respectively	114
Additional paid-in capital	82,447
Retained earnings	165,385		161,364
Accumulated other comprehensive loss	(6,416)
Total Shareholders’ Equity	241,530
Total Liabilities and Shareholders’ Equity	613,784
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Current Assets
Cash and cash equivalents	0		$ 0
Accounts receivable, net of allowance for doubtful accounts of $1,212 and $868 at September 29, 2018 and December 31, 2017, respectively	0
Contract assets	(88,066)	68,739
Inventories	59,679	(39,002)
Production cost of contracts	0
Other current assets	(524)
Total Current Assets	(28,911)
Property and equipment, net of accumulated depreciation of $159,010 and $143,216 at September 29, 2018 and December 31, 2017, respectively	0
Goodwill	0
Intangibles, net	0
Non-current deferred income taxes	130	(95)
Other assets	0
Total Assets	(28,781)
Current Liabilities
Accounts payable	0
Contract liabilities	(15,108)	24,460
Accrued liabilities	4,105	(6,091)
Total Current Liabilities	(11,003)
Long-term debt	0
Non-current deferred income taxes	(3,751)	2,608
Other long-term liabilities	0
Total Liabilities	(14,754)
Commitments and contingencies (Notes 11, 13)
Equity [Abstract]
Common stock - $0.01 par value; 35,000,000 shares authorized; 11,409,623 and 11,332,841 shares issued and outstanding at September 29, 2018 and December 31, 2017, respectively	0
Additional paid-in capital	0
Retained earnings	(14,027)	$ 8,665
Accumulated other comprehensive loss	0
Total Shareholders’ Equity	(14,027)
Total Liabilities and Shareholders’ Equity	$ (28,781)