Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Cash flows used in operating activities:
Net income	$ 9,310	$ 5,711
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	12,820	12,724
Loss on disposal of property, plant and equipment	143	27
Bad debt expense	47	4
Stock-based compensation expense	1,491	1,581
Deferred income taxes	178	117
Changes in operating assets and liabilities:
Accounts receivable	(16,615)	1,376
Inventories	(8,166)	(4,799)
Prepaid expenses, income tax receivable and other assets	(4,689)	(2,784)
Accounts payable	2,299	(6,254)
Accrued expenses and other current liabilities	(6,575)	(12,595)
Other liabilities	(658)	(148)
Net cash used in operating activities	(10,415)	(5,040)
Cash flows used in investing activities:
Purchases of property, plant and equipment	(11,477)	(6,981)
Proceeds from disposal of property, plant and equipment	2	7
Change in restricted cash	111	16
Net cash used in investing activities	(11,364)	(6,958)
Cash flows provided by (used in) financing activities:
Repurchase of Class A Common Stock	(16,640)	(33,268)
Proceeds from exercise of stock options	19,304	13,869
Cash paid on note payable	(63)	(60)
Net proceeds from sale of investment shares	186	315
Net cash provided by (used in) financing activities	2,787	(19,144)
Change in cash and cash equivalents	(18,992)	(31,142)
Cash and cash equivalents at beginning of year	65,637	91,035
Cash and cash equivalents at end of period	46,645	59,893
Supplemental disclosure of cash flow information:
Income taxes paid	459	225
Decrease in accounts receivable for ASU 2014-09 adoption	(1,310)
Income taxes refunded		2
Increase in accounts payable for purchase of property, plant and equipment	$ 2,741	$ 1,741