Consolidated Condensed Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jul. 01, 2012
Cash flows from operating activities:
Net income	$ 32,403	$ 34,049
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	6,079	5,303
Depreciation of property, plant, and equipment	3,596	3,180
Amortization of intangible assets	1,921	2,086
Amortization of discounts or premiums on investments	1,443	3,582
Realized gain on sale of investments	(83)	(1,071)
Tax effect of stock option exercises	(2,773)	(2,969)
Change in deferred income taxes	(1,748)	(1,076)
Unrealized loss on trading securities	462
Change in operating assets and liabilities	(2,325)	(2,912)
Net cash provided by operating activities	38,975	40,172
Cash flows from investing activities:
Purchases of investments	(167,652)	(109,104)
Maturities and sales of investments	129,329	242,952
Purchases of property, plant, and equipment	(4,310)	(5,304)
Net cash provided by (used in) investing activities	(42,633)	128,544
Cash flows from financing activities:
Issuance of common stock under stock option plans	16,242	13,929
Repurchase of common stock	(11,891)
Payment of dividends		(8,985)
Tax effect of stock option exercises	2,773	2,969
Net cash provided by financing activities	7,124	7,913
Effect of foreign exchange rate changes on cash and cash equivalents	(752)	(8,740)
Net change in cash and cash equivalents	2,714	167,889
Cash and cash equivalents at beginning of period	45,160	38,103
Cash and cash equivalents at end of period	$ 47,874	$ 205,992