Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018		Mar. 31, 2018	Mar. 25, 2017
Cash flows from operating activities:
Net income	$ 8,122		$ 8,122	$ 6,763
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	2,457			2,202
Share-based compensation expense	1,669			1,717
Deferred income taxes	506			(711)
Adjustment to contingent consideration liability	(147)
Changes in other accrued liabilities	(762)			135
Changes in other assets	265			(433)
Changes in current assets and liabilities, excluding effects from acquisitions:
Accounts receivable	(13,152)			(15,780)
Inventories	(338)			(4,730)
Accounts payable	2,920			5,445
Other current assets	(1,242)			(1,422)
Income taxes payable	(861)			690
Deferred profit	(2,465)			(2,121)
Accrued compensation, warranty and other liabilities	(6,249)			1,043
Net cash used in operating activities	(9,277)			(7,202)
Cash flows from investing activities, excluding effects from acquisitions:
Purchases of short-term investments	(18,801)			(8,080)
Sales and maturities of short-term investments	15,536			17,701
Cash paid for Kita, net of cash received				(11,716)
Purchases of property, plant and equipment	(1,074)			(1,430)
Cash received from sale of fixed assets	20
Net cash used in investing activities	(4,319)			(3,525)
Cash flows from financing activities:
Repurchases of common stock, net	(3,577)			(957)
Cash dividends paid	(1,772)			(1,606)
Payment of contingent consideration for Kita	(823)
Repayments of long-term debt	(355)			(470)
Net cash used in financing activities	(6,527)			(3,033)
Effect of exchange rate changes on cash and cash equivalents	973			1,551
Net decrease in cash and cash equivalents	(19,150)			(12,209)
Cash and cash equivalents at beginning of period	134,286	[1]		96,045
Cash and cash equivalents at end of period	115,136		115,136	83,836
Supplemental disclosure of cash flow information:
Cash paid for income taxes	2,498			2,312
Inventory capitalized as property, plant and equipment	84			42
Dividends declared but not yet paid	1,713		$ 1,713	1,614
Property, plant and equipment purchases included in accounts payable	$ 247			$ 56

[1] Derived from December 30, 2017 audited financial statements