CONSOLIDATED CONDENSED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Apr. 01, 2012
Cash flows from operating activities:
Net income	$ 15,583	$ 14,282
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	3,298	3,314
Depreciation of property, plant, and equipment	1,828	1,551
Amortization of intangible assets	961	1,043
Amortization of discounts or premiums on investments	758	1,835
Realized gain on sale of investments	(31)	(94)
Tax effect of stock option exercises	(1,376)	(2,838)
Change in deferred income taxes	(1,371)	(179)
Change in operating assets and liabilities	(860)	(6,060)
Net cash provided by operating activities	18,790	12,854
Cash flows from investing activities:
Purchases of investments	(76,694)	(56,721)
Maturities and sales of investments	48,248	37,188
Purchases of property, plant, and equipment	(1,908)	(2,487)
Net cash used in investing activities	(30,354)	(22,020)
Cash flows from financing activities:
Issuance of common stock under stock option plans	9,168	13,104
Payment of dividends		(4,271)
Tax effect of stock option exercises	1,376	2,838
Net cash provided by financing activities	10,544	11,671
Effect of foreign exchange rate changes on cash	(1,383)	951
Net change in cash and cash equivalents	(2,403)	3,456
Cash and cash equivalents at beginning of period	45,160	38,103
Cash and cash equivalents at end of period	$ 42,757	$ 41,559