Adoption of Accounting Standards Codification 606 - Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net Income	$ 1,591	$ 3,823	$ 4,191	$ 5,938
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Depreciation and amortization	6,334	5,748	12,315	11,530
Property and equipment impairment due to restructuring			4,375	0
Stock-based compensation expense			2,115	3,164
Deferred income taxes			3,966	478
(Recovery of) provision for doubtful accounts			(30)	41
Other			9,050	(2,286)
Changes in Assets and Liabilities:
Accounts receivable			11,172	(5,767)
Contract assets			(81,663)	0
Inventories			29,417	(9,502)
Production cost of contracts			160	(1,777)
Other assets			1,475	938
Accounts payable			20,117	14,998
Contract liabilities			15,164	0
Accrued and other liabilities			(5,597)	(1,508)
Net Cash Provided by Operating Activities			26,227	16,247
Cash Flows from Investing Activities
Purchases of property and equipment			(7,513)	(16,242)
Proceeds from sale of assets			67	3
Payments for acquisition of Certified Thermoplastics Co., LLC, net of cash acquired			(30,993)	0
Net Cash Used in Investing Activities			(38,439)	(16,239)
Cash Flows from Financing Activities
Borrowings from senior secured revolving credit facility			189,600	123,000
Repayments of senior secured revolving credit facility			(175,000)	(110,800)
Net cash paid upon issuance of common stock under stock plans			(1,006)	(2,265)
Net Cash Provided by (Used in) Financing Activities			13,594	(68)
Net Increase (Decrease) in Cash and Cash Equivalents			1,382	(60)
Cash and Cash Equivalents at Beginning of Period			2,150	7,432
Cash and Cash Equivalents at End of Period	3,532	$ 7,372	3,532	$ 7,372
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	(2,541)		(4,259)
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			(3,606)
(Recovery of) provision for doubtful accounts			0
Other			(7,661)
Changes in Assets and Liabilities:
Accounts receivable			0
Contract assets			81,663
Inventories			(53,730)
Production cost of contracts			0
Other assets			(1,494)
Accounts payable			0
Contract liabilities			(15,164)
Accrued and other liabilities			4,251
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 (Used in) 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	(950)		(68)
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Depreciation and amortization			12,315
Property and equipment impairment due to restructuring			4,375
Stock-based compensation expense			2,115
Deferred income taxes			360
(Recovery of) provision for doubtful accounts			(30)
Other			1,389
Changes in Assets and Liabilities:
Accounts receivable			11,172
Contract assets			0
Inventories			(24,313)
Production cost of contracts			160
Other assets			(19)
Accounts payable			20,117
Contract liabilities			0
Accrued and other liabilities			(1,346)
Net Cash Provided by Operating Activities			26,227
Cash Flows from Investing Activities
Purchases of property and equipment			(7,513)
Proceeds from sale of assets			67
Payments for acquisition of Certified Thermoplastics Co., LLC, net of cash acquired			(30,993)
Net Cash Used in Investing Activities			(38,439)
Cash Flows from Financing Activities
Borrowings from senior secured revolving credit facility			189,600
Repayments of senior secured revolving credit facility			(175,000)
Net cash paid upon issuance of common stock under stock plans			(1,006)
Net Cash Provided by (Used in) Financing Activities			13,594
Net Increase (Decrease) in Cash and Cash Equivalents			1,382
Cash and Cash Equivalents at Beginning of Period			2,150
Cash and Cash Equivalents at End of Period	$ 3,532		$ 3,532