Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 27,086	$ 28,938
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,451	14,262
Provision for doubtful accounts	40	(143)
Provision for warranty and returns	124	291
Stock compensation	4,133	4,361
Loss (gain) on disposal of property and equipment	(20)	41
Bond premium amortization	2,045	1,660
Cash provided (used) by changes in operating assets and liabilities
Accounts receivable	(2,538)	(9,790)
Inventories	2,471	2,974
Prepaid expenses and other assets	1,572	792
Accounts payable	(790)	(943)
Accrued liabilities	(1,236)	682
Prepaid and deferred income taxes	(5,094)	(2,194)
Net cash provided by operating activities	42,244	40,931
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(15,223)	(13,208)
Proceeds from sale of asset	21	10
Intangible assets acquired	(839)	(951)
Purchases of investment securities	(71,919)	(78,534)
Proceeds from sale of investment securities	76,681	60,452
Net cash used by investing activities	(11,279)	(32,231)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of stock options	5,016	13,214
Proceeds from employee stock purchase plan	2,457	2,220
Tax benefits from exercise of stock options	4,567	4,002
Treasury stock acquired - share awards swap for tax payments	3,033	0
Net cash provided by financing activities	9,007	19,436
Effect of exchange rate changes on cash	1,158	(202)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	41,130	27,934
CASH AND CASH EQUIVALENTS, beginning of period	146,900	99,590
CASH AND CASH EQUIVALENTS, end of period	188,030	127,524
NON-CASH INVESTING ACTIVITIES
Accrued liabilities for property and equipment	$ 273	$ 288