Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 18,963	$ 27,086
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,642	14,451
Provision for doubtful accounts	3	40
Provision for warranty and returns	(488)	124
Stock compensation	6,990	4,133
Loss (gain) on disposal of property and equipment	8	(20)
Bond premium amortization	1,599	2,045
Cash provided (used) by changes in operating assets and liabilities
Accounts receivable	9,433	(2,538)
Inventories	(4,655)	2,471
Prepaid expenses and other assets	2,146	1,572
Accounts payable	681	(790)
Accrued liabilities	2,123	(1,236)
Income taxes, including excess tax benefits and deferred income taxes	(3,098)	(5,094)
Net cash provided by operating activities	48,347	42,244
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(14,924)	(15,223)
Proceeds from sale of asset	5	21
Intangible assets acquired	(709)	(839)
Purchases of investment securities	(78,993)	(71,919)
Proceeds from sale of investment securities	69,470	76,681
Net cash used by investing activities	(25,151)	(11,279)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of stock options	9,105	5,016
Proceeds from employee stock purchase plan	2,485	2,457
Tax benefits from exercise of stock options	2,734	4,567
Purchase of treasury stock	(5,836)	(3,033)
Net cash provided by financing activities	8,488	9,007
Effect of exchange rate changes on cash	(5,465)	1,158
NET INCREASE IN CASH AND CASH EQUIVALENTS	26,219	41,130
CASH AND CASH EQUIVALENTS, beginning of period	226,022	146,900
CASH AND CASH EQUIVALENTS, end of period	252,241	188,030
NON-CASH INVESTING ACTIVITIES
Accrued liabilities for property and equipment	$ 100	$ 273