Adoption of Accounting Standards Codification 606 - Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income	$ 4,171	$ 4,655	$ 8,362	$ 10,593
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Depreciation and amortization	6,320	5,619	18,635	17,149
Property and equipment impairment due to restructuring			5,784	0
Stock-based compensation expense			3,414	4,264
Deferred income taxes			3,446	(164)
Provision for doubtful accounts			344	125
Other			9,275	(2,217)
Changes in Assets and Liabilities:
Accounts receivable			10,771	(1,427)
Contract assets			(88,066)	0
Inventories			22,909	(15,529)
Production cost of contracts			(1,447)	(599)
Other assets			3,709	458
Accounts payable			22,610	13,801
Contract liabilities			15,108	0
Accrued and other liabilities			(1,452)	903
Net Cash Provided by Operating Activities			33,402	27,357
Cash Flows from Investing Activities
Purchases of property and equipment			(12,796)	(24,599)
Proceeds from sale of assets			117	3
Payments for acquisition of Certified Thermoplastics Co., LLC, net of cash acquired			(30,711)	0
Net Cash Used in Investing Activities			(43,390)	(83,486)
Cash Flows from Financing Activities
Borrowings from senior secured revolving credit facility			239,700	320,500
Repayments of senior secured revolving credit facility			(227,100)	(255,800)
Net cash paid upon issuance of common stock under stock plans			(1,189)	(2,311)
Net Cash Provided by Financing Activities			11,411	52,386
Net Increase (Decrease) in Cash and Cash Equivalents			1,423	(3,743)
Cash and Cash Equivalents at Beginning of Period			2,150	7,432
Cash and Cash Equivalents at End of Period	3,573	$ 3,689	3,573	$ 3,689
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income	(1,216)		(5,475)
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Depreciation and amortization			0
Property and equipment impairment due to restructuring			0
Stock-based compensation expense			0
Deferred income taxes			(3,751)
Provision for doubtful accounts			0
Other			(6,463)
Changes in Assets and Liabilities:
Accounts receivable			0
Contract assets			88,066
Inventories			(59,679)
Production cost of contracts			0
Other assets			(3,644)
Accounts payable			0
Contract liabilities			(15,108)
Accrued and other liabilities			6,054
Net Cash Provided by Operating Activities			0
Cash Flows from Investing Activities
Purchases of property and equipment			0
Proceeds from sale of assets			0
Payments for acquisition of Certified Thermoplastics Co., LLC, net of cash acquired			0
Net Cash Used in Investing Activities			0
Cash Flows from Financing Activities
Borrowings from senior secured revolving credit facility			0
Repayments of senior secured revolving credit facility			0
Net cash paid upon issuance of common stock under stock plans			0
Net Cash Provided by Financing Activities			0
Net Increase (Decrease) in Cash and Cash Equivalents			0
Cash and Cash Equivalents at Beginning of Period			0
Cash and Cash Equivalents at End of Period	0		0
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income	2,955		2,887
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Depreciation and amortization			18,635
Property and equipment impairment due to restructuring			5,784
Stock-based compensation expense			3,414
Deferred income taxes			(305)
Provision for doubtful accounts			344
Other			2,812
Changes in Assets and Liabilities:
Accounts receivable			10,771
Contract assets			0
Inventories			(36,770)
Production cost of contracts			(1,447)
Other assets			65
Accounts payable			22,610
Contract liabilities			0
Accrued and other liabilities			4,602
Net Cash Provided by Operating Activities			33,402
Cash Flows from Investing Activities
Purchases of property and equipment			(12,796)
Proceeds from sale of assets			117
Payments for acquisition of Certified Thermoplastics Co., LLC, net of cash acquired			(30,711)
Net Cash Used in Investing Activities			(43,390)
Cash Flows from Financing Activities
Borrowings from senior secured revolving credit facility			239,700
Repayments of senior secured revolving credit facility			(227,100)
Net cash paid upon issuance of common stock under stock plans			(1,189)
Net Cash Provided by Financing Activities			11,411
Net Increase (Decrease) in Cash and Cash Equivalents			1,423
Cash and Cash Equivalents at Beginning of Period			2,150
Cash and Cash Equivalents at End of Period	$ 3,573		$ 3,573