CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 12,363	$ 10,903
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	3,971	3,975
Amortization of intangibles	1,856	1,842
Loss on sale of property and equipment	159	0
Stock-based compensation expense	3,915	3,636
Amortization of premium on marketable securities	394	104
Deferred income taxes	3,864	(3,236)
Reduction in accounts receivable allowances	(15)	(20)
Change in operating assets and liabilities:
Accounts receivable	(4,017)	(7,393)
Inventories	(5,652)	893
Prepaid expenses and other assets	1,825	3,928
Accounts payable	1,088	2,832
Taxes payable and accrued liabilities	(5,624)	1,172
Deferred income on sales to distributors	2,116	2,936
Net cash provided by operating activities	16,243	21,572
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(4,465)	(3,950)
Purchases of marketable securities	(24,751)	(19,422)
Proceeds from maturities of marketable securities	0	1,500
Net cash used in investing activities	(29,216)	(21,872)
CASH FLOWS FROM FINANCING ACTIVITIES:
Issuance of common stock under employee stock plans	7,045	8,705
Payments of dividends to stockholders	(3,033)	(2,310)
Net cash provided by financing activities	4,012	6,395
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(8,961)	6,095
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	92,928	63,394
CASH AND CASH EQUIVALENTS AT END OF PERIOD	83,967	69,489
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Unpaid property and equipment	4,602	1,469
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash refund for income taxes, net of payments	$ (1,942)	$ (3,698)