Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Apr. 01, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 1,797		$ 2,150	$ 7,114	$ 7,432
Accounts receivable, net of allowance for doubtful accounts of $725 and $868 at March 31, 2018 and December 31, 2017, respectively	64,915		74,064
Contract assets	78,163	$ 68,739	0
Inventories	85,932	83,159	122,161
Production cost of contracts	11,181		11,204
Other current assets	12,503		11,435
Total Current Assets	254,491		221,014
Property and equipment, net of accumulated depreciation of $147,086 and $143,216 at March 31, 2018 and December 31, 2017, respectively	110,031		110,252
Goodwill	117,435		117,435
Intangibles, net	112,154		114,693
Non-current deferred income taxes	147	166	261
Other assets	3,311		3,098
Total Assets	597,569		566,753
Current Liabilities
Accounts payable	65,042		51,907
Contract liabilities	15,723	24,460	0
Accrued liabilities	22,469	22,238	28,329
Total Current Liabilities	103,234		80,236
Long-term debt	209,710		216,055
Non-current deferred income taxes	15,775	18,589	15,981
Other long-term liabilities	21,543		18,898
Total Liabilities	350,262		331,170
Commitments and contingencies (Notes 11, 13)
Shareholders’ Equity
Common stock - $0.01 par value; 35,000,000 shares authorized; 11,380,982 and 11,332,841 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	114		113
Additional paid-in capital	80,523		80,223
Retained earnings	173,652	$ 170,029	161,364
Accumulated other comprehensive loss	(6,982)		(6,117)
Total Shareholders’ Equity	247,307		235,583
Total Liabilities and Shareholders’ Equity	$ 597,569		$ 566,753